sjögren-larsson syndrome: diversity of mutations and polymorphisms in the fatty aldehyde...

MUTATION UPDATE

Sjogren-Larsson Syndrome: Diversity of Mutationsand Polymorphisms in the Fatty AldehydeDehydrogenase Gene (ALDH3A2)

William B. Rizzon and Gael Carney

Department of Pediatrics, University of Nebraska Medical Center, Omaha, Nebraska

Communicated by Jan P. Kraus

Sjogren-Larsson syndrome (SLS) is an autosomal recessive disorder characterized by ichthyosis, mentalretardation, and spastic diplegia or tetraplegia. The disease is caused by mutations in the ALDH3A2 gene (alsoknown as FALDH and ALDH10) on chromosome 17p11.2 that encodes fatty aldehyde dehydrogenase(FALDH), an enzyme that catalyzes the oxidation of long-chain aldehydes derived from lipid metabolism. InSLS patients, 72 mutations have been identified, with a distribution that is scattered throughout the ALDH3A2gene. Most mutations are private but several common mutations have been detected, which probably reflectfounder effects or recurrent mutational events. Missense mutations comprise the most abundant class (38%)and expression studies indicate that most of these result in a profound reduction in enzyme activity. Deletionsaccount for about 25% of the mutations and range from single nucleotides to entire exons. Twelve splice-sitemutations have been demonstrated to cause aberrant splicing in cultured fibroblasts. To date, more than a dozenintragenic ALDH3A2 polymorphisms consisting of SNPs and one microsatellite marker have beencharacterized, although none of them alter the FALDH protein sequence. The striking mutational diversityin SLS offers a challenge for DNA-based diagnosis, but promises to provide a wealth of information aboutenzyme structure–function correlations. Hum Mutat 26(1), 1–10, 2005. rr 2005 Wiley-Liss, Inc.

KEY WORDS: aldehyde dehydrogenase; ALDH3A2; SLS; ichthyosis; mental retardation; spasticity; fatty alcohol; fattyaldehyde

BACKGROUND

In 1957, Sjogren and Larsson described a clinically distinctsyndrome characterized by congenital ichthyosis, mental retardationand spastic diplegia or tetraplegia [Sjogren and Larsson, 1957]. Mostof the patients were from an isolated region of northern Sweden andtheir genetic lineage could be traced back to a small group ofancestors from the early 1700s. The disease exhibited an autosomalrecessive inheritance. Subsequent patients of non-Swedish ancestrywere identified throughout the world and in all ethnic groups.Today, Sjogren-Larsson syndrome (SLS) is the most widelyrecognized neuroichthyotic disorder [Theile, 1974; Rizzo, 2001].

The symptoms of SLS are fully evident in the first year or two oflife. Most patients are born prematurely [Willemsen et al., 1999a].Dry scaly skin (ichthyosis) is usually apparent at birth and has acharacteristic pruritic nature. Delayed motor development due tospastic diplegia or tetraplegia is usually seen by the end of the firstyear, resulting in impaired ambulation. Mental retardation variesfrom mild to profound. Many patients have retinopathy withdistinctive glistening white dots in a perifoveal distribution andsuffer from photophobia. Exceptional patients may lack one of themajor symptoms of SLS or have a very mild phenotype.

SLS patients have altered lipid metabolism due to deficientactivity of fatty aldehyde dehydrogenase (FALDH; E.C. 1.2.1.48)

[Rizzo et al., 1988; Rizzo and Craft, 1991; Rizzo, 2001], an enzymethat catalyzes the NAD-dependent oxidation of aliphaticaldehydes to fatty acids [Kelson et al., 1997]. FALDH is amember of a large family of aldehyde dehydrogenase (ALDH)enzymes that are subclassified according to amino acid sequence,kinetic properties, and subcellular localization [Perozich et al.,1999; Vasiliou et al., 1999]. FALDH is considered a class 3 ALDHand has been historically known as microsomal ALDH in theliterature [Rizzo et al., 2001]. The enzyme has been purified fromhuman liver [Kelson et al., 1997], rat liver [Nakayasu et al., 1978;Lindahl and Evces, 1984; Mitchell and Petersen, 1989], and rabbitintestine [Ichihara et al., 1986b]. The purified human protein is54 kD and, like other class 3 ALDHs, it is probably catalytically

Received 27 September 2004; accepted revised manuscript12 January 2005.

nCorrespondence to: Dr. Rizzo at Department of Pediatrics, Univer-sity of Nebraska Medical Center, 985456 Nebraska Medical Center,Omaha, NE 68198-5456. E-mail: [email protected]

Grant sponsor: Tobacco Settlement Fund of the State of Nebraska;Grant sponsor: National Institutes of Health; Grant number:AR44552.

DOI10.1002/humu.20181Published online inWiley InterScience (www.interscience.wiley.com).

rr2005 WILEY-LISS, INC.

HUMANMUTATION 26(1),1^10,2005

active only as a homodimer. FALDH has the ability to oxidizealiphatic aldehydes that are 6–24 carbons long, but seems to prefer16–20-carbon substrates [Kelson et al., 1997].

SLS is caused by mutations in the gene that encodes FALDH[De Laurenzi et al., 1996]. This gene has recently been renamedALDH3A2 (MIM# 270200), but was formerly known as FALDHand ALDH10. The human ALDH3A2 gene spans 31 kb andconsists of 11 exons, numbered 1–10 with an additional exon(exon 90) situated between exons 9 and 10 [Chang and Yoshida,1997; Rogers et al., 1997]. Alternate splicing of exon 90 resultsin the production of two transcripts, which encode proteinisoforms that differ at their carboxy-terminal domains [Rogerset al., 1997; Lin et al., 2000]. The most abundant transcript isderived from splicing of exons 1–10 and produces a 485–aminoacid protein. A minor transcript that accounts for less than 10% ofthe total FALDH mRNA is produced by splicing of exon 90

between exons 9 and 10, and gives rise to a variant protein isoform(FALDHv) of 508 amino acids. Expression studies indicate thatboth isoforms of FALDH have enzymatic activity (W.B.R.,unpublished results).

In addition to the two transcripts derived from alternatesplicing, Northern analysis has shown the existence of three sizesof transcripts (2.0, 3.8, and 4 kb) that arise from utilization ofdistinct polyadenylation sites in the 30 untranslated region [Rogerset al., 1997]. The longer transcripts (3.8 and 4 kb) are moreabundant in brain, heart, skeletal muscle, and pancreas, whereasthe liver has an excess of the shorter transcript.

The FALDH promoter lacks a TATA box and has multiple CpG

islands [Chang and Yoshida, 1997; Rogers et al., 1997]. The

transcription start site is at nucleotide –258 in relation to the

translation initiation codon and there is a functional Sp1 binding

site 51 nucleotides further upstream [Rogers et al., 1997]. An

alternate transcription start site may exist at nucleotide –195

[Chang and Yoshida, 1997].Based on Northern analysis of human [Chang and Yoshida,

1997; Rogers et al., 1997] and rodent [Miyauchi et al., 1991; Lin

et al., 2000] species, ALDH3A2 is expressed in a variety of

tissues, particularly liver and intestine. FALDH enzyme activity

correlates with the amount of ALDH3A2 transcript. In mice,

the minor transcript encoding FALDHv generally mirrors the

amount of the major transcript, but it is slightly more abundant

in brain and testes compared to other tissues [Lin et al., 2000].

Ironically, although symptoms of SLS chiefly affect the skin and

nervous system, FALDH enzyme activity is not particularly high in

these two tissues compared to liver, intestine, and kidney.Density gradient centrifugation studies establish that FALDH is

localized to the microsomal fraction in human liver [Kelson et al.,

1997]. The rat FALDH protein is synthesized on free polysomes

and then inserted into the endoplasmic reticulum [Takagi et al.,

1985]. Deletion mutagenesis experiments reveal that the carboxy-

terminal 35 amino acids define a hydrophobic domain that is

necessary for anchoring the enzyme to the microsomal membrane

[Masaki et al., 1994]. In humans and mice, the carboxy-terminal

domains of both protein isoforms derived from alternate splicing

are enriched in hydrophobic amino acid residues, suggesting that

both forms of the protein are membrane-bound.FALDH gene expression is subject to physiologic regulation

in vivo [Demozay et al., 2004]. Gene expression is increased inliver and white adipose tissue of rats treated with insulin, whereasdiabetic mice exhibit a reduced expression of the FALDH genecompared to nondiabetic animals. Moreover, gene expression inrats is increased after feeding compared to fasted animals. In

addition, ALDH3A2 mRNA levels are increased in mouse liver bytreatment with clofibrate, a hypolipidemic drug that interacts withthe peroxisome proliferator-activated receptor [Vasiliou et al.,1996].

MUTATIONSAND POLYMORPHISMS

To date, 72 mutations have been identified in SLS probandsfrom 121 families (Table 1). These include missense and nonsensemutations, deletions and insertions, splicing defects, and severalcomplex mutations with combinations of nucleotide substitutions,deletions, insertions, or duplications. As shown in Figure 1, themutations are distributed throughout the gene and involve allexons, except for exons 90 and 10. A total of 41 of the mutations(56%) are single nucleotide substitutions. Of these, 27 aretransitions and 14 are transversions. Seven nucleotide substitu-tions occur at CpG dinucleotides.

Most mutations appear to be private and 55% of the SLSprobands are homozygous, probably reflecting founder effects orinbreeding. At least one mutant allele was identified in all SLSpatients investigated, but three patients, all compound hetero-zygotes of European descent, possessed one allele with nodetectable mutation in the protein coding region [Tsukamotoet al., 1997; Sillen et al., 1998b; Rizzo et al., 1999; Carney et al.,2004].

It is notable that no benign coding change has been identifiedin the ALDH3A2 gene, perhaps due to ascertainment bias inselecting for SLS patients who had previously been shown to haveFALDH deficiency. Some SLS patients, however, have beeninvestigated by DNA sequencing alone, without prior enzymaticconfirmation of the diagnosis. Except for limited screening ofspecific mutations and polymorphisms, no systematic population-based analysis of the gene has been performed to search for aminoacid changes in normal individuals.

Missense Mutations

Missense mutations account for 38% of the known mutations inALDH3A2 and are scattered throughout the gene (Fig. 1). A totalof 28 mutations have been found to alter 27 amino acid residues,with two mutations (c.551C4G and c.551C4T) changing thesame T184 residue to arginine and methionine, respectively. Atotal of 21 missense mutations have been expressed in hetero-logous systems using Chinese hamster ovary cells [Rizzo et al.,1999; Carney et al., 2004] or baculovirus-infected insect cells [DeLaurenzi et al., 1997]. With one exception (c.798G4C; p.K266N,see below), the mutant enzymes were found to possess little or nocatalytic activity (Table 1).

Missense mutations in ALDH3A2 pinpoint critical amino acidresidues necessary for FALDH catalytic activity. The missensemutations identified to date cover only 7% of the amino acidresidues in the major isoform of FALDH. Although the three-dimensional protein structure of FALDH has not been elucidated,a related rat cytosolic class 3 ALDH has been crystallized and itsstructure solved [Liu et al., 1997]. This rat protein shares 65%amino acid identity with human FALDH, but lacks thehydrophobic carboxy-terminal domain seen in the human protein.Nevertheless, it is highly likely that the basic structure of humanFALDH closely resembles that of the rat protein. Notably, theamino acid residues mutated in SLS patients share 89% identitywith the rat protein, indicating that they tend to be more highlyconserved across species and perhaps less tolerant of change withrespect to enzyme function compared to the protein at large [Rizzo

2 HUMANMUTATION 26(1),1^10,2005

TABLE

1.Mutations

intheALDH3A2Gen

eDetec

tedin

SLS

Type

ofmutation

Intron/exo

nNuc

leotide

chan

gea

Pro

tein

ortran

scriptc

han

ged,e

ALD

H3A2

hap

lotype

fReferen

ce

Misse

nse

Ex1

c.80C4T

p.L27

PWillemse

net

al.[20

01a]

Ex1

c.13

3A4T

p.I45F(9%

residu

alen

zymeac

tivity)

1Rizzo

etal.[19

99]

Ex2

c.19

1T4A

p.V64D

(o1%

residu

alen

zymeac

tivity)

3Rizzo

etal.[19

99]

Ex2

c.31

7T4G

p.L1

06R(o

1%

residu

alen

zymeac

tivity)

3Sillenet

al.[19

98b];Rizzo

etal.[19

99]

Ex2

c.34

1C4T

p.P114L(o

1%

residu

alen

zymeac

tivity)

1Rizzo

etal.[19

99]

Ex2

c.36

2C4T

p.P12

1L(o

1%

residu

alen

zymeac

tivity)

3Rizzo

etal.[19

99]

Ex4

c.55

1C4G

p.T18

4R(o

1%

residu

alen

zymeac

tivity)

2Rizzo

etal.[19

99]

Ex4

c.55

1C4Tb

p.T18

4M

(o1%

residu

alen

zymeac

tivity)

1,2

Rizzo

etal.[19

99];W

illemse

net

al.[20

01a]

Ex4

c.55

4G4C

p.G18

5A(1%

residu

alen

zymeac

tivity)

1Rizzo

etal.[19

99]

Ex4

c.641

G4A

p.C21

4Y

1DeLau

renz

ieta

l.[1996]

Ex4

c.67

8C4G

p.C22

6W

Sillenet

al.[19

98b]

Ex5

c.682

C4Tb

p.R22

8C

(9%

residu

alen

zymeac

tivity)

2,3

Rizzo

etal.[19

99]

Ex5

c.71

0G4A

p.C23

7Y(o

1%

residu

alen

zymeac

tivity)

1Rizzo

etal.[19

99]

Ex5

c.73

3G4Ab

p.D24

5N

(1%

residu

alen

zymeac

tivity)

Sillenet

al.[19

98b];Rizzo

etal.[19

99];

Willemse

net

al.[20

01a]

Ex5

c.79

8G4C

p.K26

6N

(55%

residu

alen

zymeac

tivity);

unstab

letran

script

2Rizzo

etal.[19

99];W

illemse

net

al.[20

01a]

Ex6

c.83

5T4A

p.Y27

9N

(o1%

residu

alen

zymeac

tivity)

3Rizzo

etal.[19

99];K

raus

etal.[20

00]

Ex7

c.94

3C4T

p.P31

5S(o

1%

residu

alen

zymeac

tivity)

1DeLau

renz

ieta

l.[1997

];Sillenet

al.[19

97b];

Rizzo

etal.[19

99];IJlst

etal.[19

99]

Ex7

c.98

4G4C

p.M32

811

Rizzo

etal.[19

99]

Ex7

c.10

94C4Tb

p.S365

L(3%

residu

alen

zymeac

tivity)

1,2

Sillenet

al.[19

98b];Rizzo

etal.[19

99]

Ex8

c.11

39G4A

p.S380

N(o

1%

residu

alen

zymeac

tivity)

3Carne

yet

al.[20

04]

Ex8

c.11

57A4G

p.N386S

Aoki

etal.[20

00]

Ex9

c.12

16G4A

p.G40

6R

2Rizzo

etal.[19

99]

Ex9

c.12

31C4T

p.H41

1Y(o

1%

residu

alen

zymeac

tivity)

4Rizzo

etal.[19

99]

Ex9

c.12

34G4Ab

p.G41

2R

Sillenet

al.[19

98b]

Ex9

c.12

44G4A

p.S41

5N

(o1%

residu

alen

zymeac

tivity)

2Rizzo

etal.[19

99]

Ex9

c.12

56T4C

p.F41

9S(3%

residu

alen

zymeac

tivity)

4Rizzo

etal.[19

99]

Ex9

c.12

68G4Ab

p.R42

3H

(1%

residu

alen

zymeac

tivity)

3Rizzo

etal.[19

99]

Ex9

c.13

39A4G

p.K447

E(1%

residu

alen

zymeac

tivity)

1Rizzo

etal.[19

99]

Deletion

Ex1

c.21

_ 46de

lp.R7fs

Willemse

net

al.[20

01a]

Ex1

c.10

3de

lCp.Q35

fsSillenet

al.[19

98b]

Ex2

c.28

6_ 2

96de

lp.Y96fs

3Rizzo

etal.[19

99]

Ex2

c.33

8de

lAp.Y11

3fs

3Rizzo

etal.[19

99]

Ex2

c.37

4_ 378

del

p.A12

5fs

2Rizzo

etal.[19

99]

Ex3

c.469

delC

p.Q15

7fs

1Rizzo

etal.[19

99]

Ex4

c.52

1delT

p.L1

74fs

1DeLau

renz

ieta

l.[1996]

Ex6

c.80

8de

lGp.G27

0fs

2DeLau

renz

ieta

l.[1996]

Ex6

c.82

1_ 822

delA

Ap.K27

4fs

3Rizzo

etal.[19

99]

Ex6

c.906de

lTp.F30

2fs

Kraus

etal.[20

00]

Ex7

c.968de

lCp.P32

3fs

1Rizzo

etal.[19

99]

Ex7

c.11

00de

lAp.N367

fs3

Rizzo

etal.[19

99]

Ex9

c.12

23de

lGp.G40

8fs

1Carne

yet

al.[20

04]

Ex9

c.12

91_ 129

2de

lAA

p.K43

1fs

2Rizzo

etal.[19

99]

Ex9

c.12

97_ 129

8de

lGA

p.E43

3fs

(o1%

residu

alen

zymeac

tivity)

1Tsuk

amoto

etal.[19

97];Rizzo

etal.[19

97];Sillenet

al.

[1998

b];IJlste

tal.[1999];L

inet

al.(un

publis

hed

)Ex9

c.13

84_ 1387

delG

AAA

p.E462

fsWillemse

net

al.[19

99b];Willemse

net

al.[20

01a]

Ex9

c.Exo

n9de

letion

p.G40

3fs

Sillenet

al.[19

98b];Kraus

etal.[20

00]

HUMANMUTATION 26(1),1^10,2005 3

Insertionan

ddu

plic

ation

Ex2

c.28

9_ 354du

pc

p.L1

22Qins2

21

Carne

yet

al.[20

04]

Ex4

c.487

_ 488insA

p.I163fs

Willemse

net

al.[20

01a]

Ex4

c.62

0_ 6

21insG

p.G20

7fs

3Rizzo

etal.[19

99]

Ex6

c.865

_ 866insT

p.K28

9fs

Sillenet

al.[19

98b]

Ex9

c.12

23_ 122

4insG

p.G40

8fs

4Carne

yet

al.[20

04]

Ex9

c.12

50_ 126

5du

pp.Q42

2fs

1Carne

yet

al.[20

04]

Ex9

c.13

07_ 131

1dup

ACAAA

p.L43

8fs

Tsuk

amoto

etal.[19

97];Rizzo

etal.[19

99]

Com

plex

Int1

-Int2

c.15

3+5_ 3

87-4

08de

lins19

p.S52

_A12

8de

lfsRizzo

etal.[19

99]

Ex5+Ex6

[c.733

G4A;c.901

G4C;

c.906de

lT;c.909T4G]

[p.D

245N

(+)p

.A30

1P(+

)p.F

302fs]

2Sillenet

al.[19

98b]

Ex7

c.94

1_ 943

delC

CCins2

1p.A31

4_P31

5de

lins

GAKSTVGA

1DeLau

renziet

al.[19

96];Tsu

kamoto

etal.[19

97];

Sillenet

al.[19

98b]

Ex8

c.11

08_ 111

6de

linsA

CAG

p.L37

0fs

3Rizzo

etal.[19

99]

Nons

ense

Ex1

c.24

-25CC4TT

p.R9X

1Rizzo

etal.[19

99]

Ex1

c.28

C4T

p.Q10

X3

Rizzo

etal.[19

99]

Ex2

c.23

3G4A

p.W

78X

3Rizzo

etal.[19

99]

Ex4

c.52

9C4Tb

p.R17

7X

2Carne

yet

al.[20

04]

Ex9

c.12

77T4G

p.L42

6X

Kraus

etal.[20

00]

Splic

e-site

Int2

c.38

5+2T4C

Skipsex

on2-

r.154_ 3

85de

land

p.S52

_ 129

delfs

Kraus

etal.[20

00]

Int3

c.47

1+1d

elG

Skipsex

ons

2an

d3-

r.154_ 471

dela

ndp.52

_ 157

del

2Rizzo

etal.[19

99];K

raus

etal.[20

00]

Int3

c.47

1+1G

4C

Skipsex

ons

2an

d3-

r.154_ 471

dela

ndp.52

_ 157

del

Kraus

etal.[20

00]

Int3

c.47

1+2T4G

Skipsex

ons

2an

d3-

r.154_ 471

dela

ndp.52

_ 157

del

3Rizzo

etal.[19

99]

Int3

c.47

2-2

A4G

Skipsinitial3

3bp

inex

on4an

dutilize

sdo

wnstream

cryp

ticac

ceptors

itein

exon

4-

r.472

_ 504

dela

ndp.15

8_ 168de

l

3Rizzo

etal.[19

99]

Int4

c.681

-2A4G

Skipsex

ons

5-

r.681

_ 798

dela

ndp.R22

7fs

3Rizzo

etal.[19

99]

Int4

c.681

-14T4A

Cau

sesutiliza

tionof

ane

wcryp

ticac

ceptor

site

inintron4ad

ding24

bpbe

twee

nex

ons

4an

d5-

r.681

-14u4a,

680

_ 681

ins2

4an

dp.C22

26_R22

7ins8

1Rizzo

etal.[19

99]

Skipsex

on5-

r.681

_ 798

dela

ndp.R22

7fs

Int5

c.79

8+5G4A

Skipsex

on5-

r.681

_ 798

dela

ndp.R22

7fs

Skipsex

ons

4an

d5-

r.472

_ 798

dela

ndp.D15

8_K26

6de

l

3Rizzo

etal.[19

99]

Int5

c.79

8+1de

lGSkipsex

on5-

r.681

_ 798

dela

ndp.R22

7fs

Skipsex

ons

4an

d5-

r.472

_ 798

dela

ndp.D15

8_K26

6de

l

1Rizzo

etal.[19

99]

Int5

c.79

8+1_ 798+6de

lGTTTGT

Skipsex

on5-

r.681

_ 798

dela

ndp.R22

7fs

Skipsex

ons

4an

d5-

r.472

_ 798

dela

ndp.D15

8_K26

6de

l

1Rizzo

etal.[19

99]

Int7

c.11

07+2T4G

Skipsex

on7-

r.941

_ 110

7de

land

p.A31

4fs

Skipsex

ons

6-8

-r.7

99_ 120

7de

land

p.E26

7_G40

3de

lfs

3Carne

yet

al.[20

04]

Minor

amou

nto

fnor

mal

tran

script-

r.=

TABLE

1.(continu

ed)

Typeof

mutation

Intron/exo

nNuc

leotide

chan

gea

Protein

ortrans

criptc

han

ged,e

ALD

H3A2

hap

lotype

fReferen

ce


et al., 2001]. In SLS patients, no amino acid substitutions havebeen found in the hydrophobic membrane-binding domain at thecarboxy-terminus of the FALDH protein.

Comparison of the human FALDH protein with the rat class 3ALDH crystal structure provides insight into the effects of aminoacid substitutions on protein structure and catalytic function. Forexample, the c.733G4A (p.D245N) mutation replaces asparticacid 245 with asparagine and results in a protein with 1% ofnormal catalytic activity [Rizzo et al., 1999]. Aspartic acid 245 inhuman FALDH is equivalent to aspartic acid 247 in thehomologous rat class 3 protein [Liu et al., 1997]. In the ratenzyme, aspartic acid 247 is important for maintaining thegeometric structure of the active site by forming key hydrogenbonds with lysine 213 in the catalytic domain and isoleucine 334on the protein chain. Replacement of aspartic acid 247 withasparagine eliminates the hydrogen bonds and results in a mutantenzyme with a profound reduction in the Vmax and a minimalchange in Km [Hempel et al., 2001].

One mutation in ALDH3A2, while ostensibly directing anamino acid replacement, may have pleiotropic effects on geneexpression. The c.798G4C mutation alters the last nucleotide inexon 5 and is predicted to result in a p.K266N replacement in theFALDH protein; however, the mutant protein possesses consider-able (55%) residual catalytic activity when expressed in Chinesehamster cells [Rizzo et al., 1999]. The SLS patient who carried thismutation was a compound heterozygote and had a second allelecontaining the c.943C4T (p.P315S) missense mutation. Uponamplification of the patient’s fibroblast mRNA, only thec.943C4T transcript was detectable, suggesting that the transcriptbearing the c.798G4C mutation was poorly expressed orrapidly degraded, presumably due to aberrant splicing. Thus, it islikely that the c.798G4C mutation is not expressed at the proteinlevel.

The c.943C4T mutation has historical significance because itis the cause of SLS in most Swedish patients originally described bySjogren and Larsson [De Laurenzi et al., 1997; Sillen et al.,1997b]. This mutation is also carried by many northern Europeanpatients, who share an identical ALDH3A2 haplotype with theSwedish patients. These findings are consistent with a foundereffect and prompted speculation that the c.943C4T allele wasspread to the northern European continent by migration of theVikings during the 9th and 10th centuries [De Laurenzi et al.,1997].

Deletions

Approximately one-fourth of the mutations in the ALDH3A2gene are deletions (Table 1). Three deletions are at splice-sitesand are listed as splicing mutations in Table 1. The deletions rangein size from a single nucleotide to an entire exon and aredistributed throughout the gene (Fig. 1). Most deletions haveconsisted of one or two nucleotides only. The larger deletions tendto be more complicated, involving both deletion and insertion ofnucleotides, and are therefore classified as complex mutations inTable 1.

Two deletions in exon 9, c.1291_1292delAA (p.K431fs) andc.1297_1298delGA (p.E433fs), involve the same 9-bp palindromicsequence (AAGAGAGAA). The c.1297_1298delGA deletion isthe most common mutation seen among SLS patients of Europeanheritage, accounting for 26% of the mutant alleles in one series of21 probands [Rizzo et al., 1997].

The largest deletion in the ALDH3A2 gene is 6 kb and resultsin complete loss of exon 9 [Sillen et al., 1998b; Kraus et al., 2000].

Int7

c.11

08-1G4C

Skipsex

on8-

r.110

8_ 120

7de

land

p.L37

0_G40

3fs

1Rizzo

etal.[19

99]

Skipsex

ons

8-9

-r.110

8_ 1443

dela

ndp.L37

0_K48de

laMutations

arenam

edus

ingthecD

NAse

quen

celis

tedin

Gen

Ban

k(acc

essionNM_00

0382

.1)inwhichtheAof

theinitiatorA

TG

codo

nis

design

ated

+1.

b Trans

itionmutationat

CpG

dinu

cleo

tide

.c Thismutationwas

errone

ouslynam

edas

c.29

9_ 3

65du

pbyCarne

yet

al.[20

04].

dAllprotein

chan

geswerede

duce

dfrom

thenu

cleo

tide

chan

ges,wherea

sch

ange

sin

thetran

scripta

risingfrom

splic

e-site

mutations

wereex

perim

entallyde

term

ined

.e N

umbe

rsin

paren

thes

esindica

tetheresidu

alen

zymeca

talyticac

tivity

ofm

utan

tFALDH

protein

expressed

inChines

eham

ster

ovaryce

llsas

ape

rcen

tage

ofthat

seen

withwild-typeFA

LDH

protein.

f Hap

lotypes

wereco

nstructed

using4

intrag

enic

SNPs(see

Table

2)an

darede

¢ne

das

follow

s:hap

lotype1:

[c.153

+1T

;c.47

1+31

C;c.94

0+53

C;c.14

46T];

hap

lotype2:

[c.153

+1C

;c.47

1+31

T;c.94

0+53

G;

c.14

46T];hap

lotype

3:[c.153

+1C

;c.471

+31

T;c.94

0+53

C;c

.1446A];hap

lotype

4:[c.153

+1C

;c.471

+31

T;c.94

0+53

C;c

.1446T].

TABLE

1.(continu

ed)

Typeof

mutation

Intron/exo

nNuc

leotide

chan

gea

Protein

ortrans

criptc

han

ged,e

ALD

H3A2

hap

lotype

fReferen

ce

HUMAN MUTATION 26(1),1^10,2005 5

Kraus et al. [2000] sequenced the deletion breakpoints andidentified an identical 8-bp flanking sequence at the deletionjunctions in intron 8 and intron 9, suggesting a slippage mispairingmechanism for the deletion. The mutation accounted for 5 of 18alleles in the German SLS patients studied.

Insertions and Duplications

Four single-nucleotide insertion mutations have been found inALDH3A2 (Table 1). Three additional duplication mutations,ranging from five nucleotides to 66 nucleotides in length, havebeen identified. Most of these mutations cause frameshifts and arepredicted to result in truncated proteins. The largest duplication,c.289-354dup (p.L122Qins22) is predicted to cause an amino acidsubstitution along with an in-frame insertion of 22 amino acids inthe FALDH protein [Carney et al., 2004].

Complex Mutations

Three complex mutations in ALDH3A2 involve combinationsof deletions and insertions. A common mutation seen in SLSpatients originating from the Mideast is c.941_943delCCCins21(p.A314_P315delinsGAKSTVGA). At least four of these osten-sibly unrelated patients have an identical intragenic haplotype,suggesting that the mutation arose in a shared ancestor [Rizzoet al., 1999].

A consanguineous Turkish patient carried a large deletionspanning more than 2 kb involving intron 1, exon 2, and a portionof intron 2 [Rizzo et al., 1999]. Sequencing across the deletionidentified the precise nucleotide breakpoints (c.153+5_387-408delins19). The downstream breakpoint in intron 2 was foundto include a 19-bp insertion that included a 10-bp duplicationfrom intron 2. A third deletion/insertion mutation(c.1108_1116delinsACAG) (p.L370fs) was identified in an Italianpatient.

An unusual ALDH3A2 allele carried by several SLS patients ofEuropean ancestry consists of four distinct nucleotide changes:c.733G4A; c.901G4C; c.906delT; and c.909T4G [Sillen et al.,1998b; Rizzo et al., 1999; Kraus et al., 2000]. Two of thesenucleotide changes (c.733G4A and c.906delT) are destructive toenzyme function and have also been found as isolated mutationsin different patients.

Splicing Defects

Twelve (16%) of the ALDH3A2 mutations involve splice sites.All have been investigated at the mRNA level and found todisrupt normal splicing [Rizzo et al., 1999; Kraus et al., 2000]. Allof the splicing mutations are predicted to have drastic effects onthe FALDH protein by deleting amino acids, inserting additionalresidues or resulting in a truncated protein.

Splice donor mutations have generally resulted in skipping oneor two upstream exons (Table 1). In contrast, the splice acceptormutations have tended to show more variable splicing errors. Onepatient carrying the c.681–14T4A mutation near the acceptorsplice site at exon 5 was found to utilize a cryptic acceptor sitefurther upstream in intron 4 [Rizzo et al., 1999]. This resulted inthe addition of 24 bp to the transcript and is predicted to cause anin-frame insertion of eight amino acids in the FALDH protein. Inaddition, a second transcript lacked exon 5. The splicing errorsfrom this mutation were not complete, since a very small amountof normal FALDH transcript was also produced. A secondmutation (c.472–2A4G) alters the consensus AG of the splice-acceptor site of exon 4 and mRNA analysis revealed the utilizationof the next available downstream AG as a cryptic acceptor site.This resulted in an in-frame deletion of the first 33 nucleotideswithin exon 4 of the mRNA and a predicted loss of 11 amino acidsfrom the FALDH protein.

SequenceVariations of Uncertain Signi¢cance

Rizzo et al. [1999] reported an SLS patient who carried thec.1268G4A (p.R423H) missense mutation in exon 9 togetherwith a single-nucleotide variation (c.1494G4A) 36 bp down-stream from the stop codon in the 30-untranslated region of exon10. No other nucleotide changes were detected by amplifyingexons from genomic DNA. When the patient’s fibroblast mRNAwas amplified by RT-PCR and sequenced, only the c.1268G4Aallele was seen, suggesting that the transcript bearing thec.1494G4A sequence variation was not expressed or was unstableand rapidly degraded. Expression studies were not performed andother family members were not examined to establish thebiological significance of the c.1494G4A change. It is unclearwhether the c.1494G4A change is a rare polymorphism, since ithas been subsequently detected in one SLS patient carrying the

FIGURE 1. Location of mutations in the ALDH3A2 gene. Exons are indicated with numbered rectangles and are drawn to scale.Introns are indicated by horizontal lines and are not drawn to scale. Only coding regions of exons 1 and 10 are shown, since nocon¢rmed disease mutations have been identi¢ed in 50 and 30 untranslated regions. Nucleotides are numbered according to thecDNA sequence listed in GenBank (accession number NM_000382.1) in which the A of the initiator codon is designated +1.Mutations shown above the gene are missense and nonsense mutations, whereas those below the gene are deletions, insertions,splicing defects, and complex changes. Nonsensemutations are indicated by an asterisk. Splice-sitemutations are underlined.


TABLE

2.Polymor

phismsin

theALDH3A2ge

nen

Exo

n/intron

loca

tion

Type

ofpolymor

phism

Nuc

leotide

pos

itiona

(cDNA)

Nuc

leotide

pos

itionb

(gen

omic)

Alle

lefreq

uenc

yReferen

cec

Intron1

SNP

c.15

3+39

C4T

g.41

2762

C4T

C:0

.71

Rizzo

etal.[19

99];refSNPrs46467

93T:

0.29

Intron2

SNP

c.38

6-135

A4T

g.41

601

1A4T

A:0

.588

refSNPrs10

0449

0T:

0.41

2Intron3

SNP

c.47

1-31

T4C

g.41

6262

T4C

T:0.73

Rizzo

etal.[19

99];refSNPrs10

0449

C:0

.27

Intron3

SNP

c.47

2-5

84C4T

g.41

9381

C4T

C:0

.577

refSNPrs962

801d

T:0.42

3Intron3

SNP

c.47

2-308

G4A

g.41

965

7G4A

G:0

.528

refSNPrs20

7233

3d

A:0

.472

Intron3

SNP

c.47

2-211

A4G

g.41

9754A4G

A:0

.275

refSNPrs962

800d

G:0

.725

Intron3

SNP

c.47

2-5

6G4A

g.41

9909G4A

G:0

.572

refSNPrs20

7233

2d

A:0

.428

Intron4

SNP

c.681

-206A4G

g.42

1138

A4G

A:0

.703

refSNPrs10

3489

7d

G:0

.297

Intron6

SNP

c.94

0+53

C4G

g.42

4920

C4G

C:0

.84

Rizzo

etal.[19

99];refSNPrs18

00869

G:0

.16

Intron6

SNP

c.94

1-701

G4A

g.42

6231

G4A

C:0

.442

refSNPrs21

0897

1d

A:0

.558

Intron8

Microsa

tellite

TG

repe

atc.12

07+33

1(TG)15_ 24

g.42

8977

(TG)15_ 24

10alleles;

freq

uenc

iesno

trepor

ted

DeLau

renz

ieta

l.[1997

];Gen

Ban

kZ67

319

(AFMa1

26yd

5)

Intron8

SNP

c.12

07+19

06A4G

g.43

0606A4G

A:0

.442

refSNPrs80

6957

6G:0

.558

Exo

n10

SNP

c.14

46A4T

g.43

9159

A4T

A:0

.51;

0.29

4Chan

gan

dYo

shida[1997

];Sillenet

al.[19

98b];

Rizzo

etal.[19

99];refSNPrs72

16T:

0.49

;0.706

Exo

n10

/30 -U

TR

SNP

c.14

58+16

09A4G

g.440

780A4G

A:0

.340

refSNPrs72

15G:0

.660

Exo

n10

/30 -U

TR

Insertion/deletion

c.14

58+18

76_ 145

8+18

77de

lAC

g.441

047_ 441

048de

lAC

AC:0

.669

refSNPrs16

420

delAC:0

.331

nOnly

those

polymor

phismsarelis

tedforw

hichallele

freq

uenc

ieshav

ebe

ende

rive

dfrom

more

than

100ch

romoso

mes.

acD

NAnu

cleo

tide

numbe

ringsystem

usingGen

Ban

kac

cessionNM_00

0382

.1.

bGen

omic

DNAnu

mberingsystem

derive

dfrom

Gen

Ban

kco

ntigac

cessionNT_03

084

3.c R

eferen

cesareto

pub

lished

literature,

Gen

Ban

kac

cessionnu

mbe

r,an

d/orp

olymor

phismslis

tedin

thedb

SNPda

tabas

eat

www.ncb

i.nlm

.gov

/SNP.

d This

SNPin

thedb

SNPda

tabas

eisreported

usingtheminus

(non-co

ding)D

NAstrand.

Forc

ons

istenc

yin

thetable,these

quen

ceva

riations

arelis

tedforthepositive

strandonly

asreported

inNT_03

0843

.SNP,

singlenu

cleo

tide

polymorp

hism.


disease-causing c.1094C4T (p.S365L) mutation (W.B.R., G.C.unpublished observations).

To date, no nucleotide variations have been reported in thepromoter region of ALDH3A2. The mutation detection strategiestaken by most groups, however, have not examined more thanseveral dozen nucleotides upstream of the coding region in exon 1.

Polymorphisms and ALDH3A2 Haplotypes

At least 15 polymorphisms have been identified within theALDH3A2 gene (Table 2). Most of the nucleotide changes areSNPs, but one polymorphism is a microsatellite TG repeat. All ofthe polymorphisms are located in noncoding regions, with theexception of one SNP (c.1446A4T) in exon 10 that alters thethird nucleotide of codon 481 and results in no amino acid change.Allele frequencies of the most characterized SNPs are listed inTable 2. None of the polymorphisms are rare.

Early haplotype studies relied on flanking microsatellite markersto localize the SLS gene and demonstrate genetic relationshipsbetween SLS patients [Pigg et al., 1994; De Laurenzi et al., 1997;Sillen et al., 1997b, 1998a, 1998b]. With the identification ofintragenic polymorphisms, haplotype analysis of the ALDH3A2gene has become more refined. Using haplotypes generated fromfour SNPs, haplotype associations were established in most of themutations reported (see Table 1) [Rizzo et al., 1999; Carney et al.,2004]. Four mutations are each found on multiple haplotypes,suggesting that they arose independently. Three of these mutations(c.551C4T, c.682C4T, and c.733G4A) occur at CpG dinucleo-tides and may represent mutational hot spots. From a practicalpoint of view, intragenic haplotypes may prove useful for diagnosticpurposes and genetic counseling in those rare SLS families inwhich mutation analysis has been unable to identify a mutantallele. For example, the ALDH3A2 allele(s) with no identifiedmutation carried by three European patients mentioned above isassociated with haplotype 1 (see Table 1 for haplotype definition).

BIOLOGICAL RELEVANCE

The study of SLS patients who carry mutations in theALDH3A2 gene has been instrumental in establishing thebiological function of FALDH. This enzyme plays a pivotal rolein metabolism of several lipids, including fatty alcohol, etherglycerolipids, phytanic acid, and leukotriene B4.

In vitro metabolic studies of SLS fibroblasts, together with thedemonstration that SLS patients accumulate hexadecanol andoctadecanol in plasma [Rizzo et al., 1988; Rizzo and Craft, 2000],have provided conclusive evidence that FALDH is responsible foroxidizing long-chain aldehydes derived from metabolism of 16–18-carbon straight-chain fatty alcohols. In this role, FALDH appearsto interact closely with fatty alcohol dehydrogenase and forms anenzyme complex, called fatty alcohol:NAD+ oxidoreductase, thatcatalyzes the complete oxidation of fatty alcohol to fatty acid [Lee,1979; Ichihara et al., 1986a].

In vitro studies of SLS fibroblasts and FALDH-deficientChinese hamster cells also implicate FALDH in the oxidation offatty aldehydes derived from metabolism of ether glycerolipids[Rizzo et al., 2000]. These lipids have an ether-linked alkyl chainattached to the first carbon of a glycerol backbone, and areprominent in certain tissues, such as in myelin, skin and heart.Metabolism of ether glycerolipids proceeds by catalytic hydrolysisof the ether-linked alkyl group released as a fatty aldehyde, whichis subsequently oxidized to fatty acid by FALDH.

There is evidence to suggest that FALDH is involved in twoseparate steps in the metabolism of phytol and phytanic acid. Phytol

is a branched-chain fatty alcohol that is derived from the diet. It ismetabolized by initial oxidation to phytanic acid, a reaction that isimpaired in cultured skin fibroblasts from SLS patients [van denBrink et al., 2004]. Phytanic acid is subsequently metabolized byremoval of the carboxyl group via alpha-oxidation. This processgenerates a fatty aldehyde (pristanal), which is subsequentlyoxidized to pristanic acid. In vitro studies on cultured SLSfibroblasts incubated with radioactive phytanic acid have demon-strated a deficiency of this oxidative step, implicating FALDH inthis second point in the pathway [Verhoeven et al., 1998].

SLS patients accumulate leukotriene B4 (LTB4), a proinflam-matory lipid mediator synthesized from arachidonic acid (a 20-carbon polyunsaturated fatty acid). LTB4 is metabolized by initialomega-hydroxylation forming 20-hydroxy-LTB4, followed byoxidation of the omega-hydroxy group to form a dicarboxylic acidin a reaction that is analogous to straight-chain fatty alcoholoxidation. Metabolism of LTB4 has been shown to be defective inleukocytes of SLS patients [Willemsen et al., 2001c]. Accumula-tion of LTB4 and/or 20-hydroxy-LTB4 appears to be responsible inpart for the pruritic nature of the ichthyosis in SLS, becausetreatment of patients with a selective inhibitor of LTB4 synthesis(Zileuton) reverses its accumulation and ameliorates the itchinessof the skin [Willemsen et al., 2001b]. This drug, however, does notimprove the ichthyosis itself or the neurologic symptoms.

It is hypothesized that the accumulation of fatty alcohol and/orformation of aldehyde adducts in biological membranes contributeto the pathogenesis of SLS in ways that are not yet defined [Rizzo,2001]. Fatty alcohol accumulation in the skin may disrupt theepidermal water barrier resulting in ichthyosis. Owing to theirhighly reactive nature, the fatty aldehyde substrates of FALDH,which cannot be metabolized to fatty acids, have the potential toform covalent Schiff base adducts with other molecules containingfree amino groups. One prominent lipid target for aldehydemodification is phosphatidylethanolamine (PE), forming N-alkyl-PE [James and Zoeller, 1997; Verhoeven et al., 1998]. Thiscovalent modification changes the polar nature of the PE moleculeand may affect membrane structure and function. Aliphaticaldehydes also have the potential to covalently modify lysineresidues in proteins, including membrane-bound enzymes thatmight exhibit altered catalytic properties.

CLINICAL RELEVANCE

Most SLS patients have the major symptoms (ichthyosis, mentalretardation, and spasticity) to more or less varying degrees. Owingto the large proportion of private mutations in SLS and manypedigrees with single cases, the influence of ALDH3A2 genotypeon clinical phenotype is difficult to judge. Furthermore, many ofthe published cases have little or no clinical information. Despitethe limited genotype–phenotype information available so far,however, it would appear that the severity of the clinicalphenotype does not closely correlate with specific mutations orresidual enzyme activity [Willemsen et al., 2001a]. Even amongsiblings who share ALDH3A2 genotypes, considerable clinicalvariation can occur. For example, one atypical SLS family hadthree affected siblings (7, 12, and 14 years of age) with no mentalretardation and quite divergent spasticity and cutaneous disease,including one sibling without ichthyosis [Nigro et al., 1996]. Thesepatients are compound heterozygotes for the commonc.1297_1298delGA mutation and a unique c.984G4C(p.M328I) mutation. In another kindred, a pair of adult siblingswho are compound heterozygotes for c.943C4T and c.551C4Texhibited ichthyosis. The male sibling had late-onset spasticity and


was feeble-minded at 36 years of age, whereas his 46-year-old sisterhad normal intellectual development and no spasticity [Willemsenet al., 2001a]. These unusual families highlight the striking clinicalvariation that can occur between SLS siblings and suggest theexistence of other genetic or environmental modifiers.

DIAGNOSTIC RELEVANCE

The ability to diagnose SLS by mutation analysis offers analternative to enzymatic testing. The FALDH enzymatic test is notwidely available and diagnostic centers rely on cultured skinfibroblasts as the source of enzyme, which requires an invasive skinbiopsy and several weeks for cells to grow. In contrast, the DNA-based diagnosis of genetic disease is now routine and themethodology is widely available. Although screening the entireFALDH gene is still time-consuming and expensive, targetedscreening for common mutations in suspected SLS patients fromcertain ethnic or geographic populations is more efficient. Forexample, c.1297-1298delGA and c.943C4T together account for36% of the alleles detected in European SLS probands [Rizzo et al.,1999], whereas the exon 9 deletion and c.906delT are the majormutations causing SLS among Bavarian patients [Kraus et al.,2000]. Similarly, c.682C4T and c.943delCCCins19nt are rela-tively common among patients of Mideastern ancestry [Rizzoet al., 1999]. Rapid screening methods, based on allele-specificPCR or restriction enzyme digestion of PCR amplicons, have beendeveloped to detect these mutations [De Laurenzi et al., 1997;Rizzo et al., 1997, 1999; Kraus et al., 2000].

Prenatal diagnosis of SLS has been accomplished by enzymaticassay of cultured amniocytes or chorionic villi cells [Rizzo et al.,1994] and mutation analysis [Sillen et al., 1997a] (W.B.R.,unpublished results). DNA-based diagnosis requires knowledge ofthe specific mutation, but is faster than enzymatic studies, whichrequire growth of fetal-derived cells.

FUTURE PROSPECTS

A more complete identification of the mutations responsible forSLS will ultimately prove useful for the reliable diagnosis of thisdisease and its prevention through genetic counseling and prenataldiagnosis. At present, the wide mutational diversity in SLS justifiesthe continuing need for a biochemical approach to the diagnosis ofthis disease, except for those populations harboring commonmutations. However, advances in mutation screening technologiesmay lead to DNA-based diagnostic tests replacing enzymaticmethods in most laboratories. In the near term, a more exhaustivedescription of the clinical phenotype of SLS patients, together withtheir mutational genotype, is sorely needed to investigategenotype–phenotype correlations and uncover possible modifiergenes. At the biochemical level, elucidation of the three-dimensional structure of FALDH will be necessary to understandthe precise molecular mechanisms whereby amino acid substitu-tions destroy catalytic function.

Although the molecular basis of SLS has been elucidated atleast in part, the next major goal is to understand the pathogenicmechanisms leading to clinical symptoms and devise methods tointerrupt or modify this process. This will require a more completeunderstanding of the role of FALDH in normal metabolism. Therare nature of the disease, reluctance of patients to provide tissuespecimens, and the lack of an animal model for SLS have hinderedmany studies. Progress has recently been achieved in generating aFALDH-deficient mouse model using gene-targeting methods(Rizzo WB, Carney G, Spieker R, Bridger J, Lin Z, Stribley J,

Salbaum M., unpublished results). The availability of such SLSmice promises to open new avenues for investigating thebiochemical basis for symptoms and developing new therapeuticapproaches to this disease.

REFERENCES

Aoki N, Suzuki H, Ito K, Ito M. 2000. A novel point mutation ofthe FALDH gene in a Japanese family with Sjorgen-Larssonsyndrome. J Invest Dermatol 114:1065–1066.

Carney G, Wei S, Rizzo WB. 2004. Sjogren-Larsson syndrome:seven novel mutations in the fatty aldehyde dehydrogenase geneALDH3A2. Hum Mutat 24:186.

Chang C, Yoshida A. 1997. Human fatty aldehyde dehydrogenasegene (ALDH10): organization and tissue-dependent expression.Genomics 40:80–85.

De Laurenzi V, Rogers GR, Hamrock DJ, Marekov LN, SteinertPM, Compton JG, Markova N, Rizzo WB. 1996. Sjogren-Larssonsyndrome is caused by mutations in the fatty aldehydedehydrogenase gene. Nat Genet 12:52–57.

De Laurenzi V, Rogers GR, Tarcsa E, Carney G, Marekov L, BaleSJ, Compton JG, Markova N, Steinert PM, Rizzo WB. 1997.Sjogren-Larsson syndrome is caused by a common mutation innorthern European and Swedish patients. J Invest Dermatol109:79–83.

Demozay D, Rocchi S, Mas JC, Grillo S, Pirola L, Chavey C, VanObberghen E. 2004. Fatty aldehyde dehydrogenase: potentialrole in oxidative stress protection and regulation of its geneexpression by insulin. J Biol Chem 279:6261–6270.

Hempel J, Kuo I, Perozich J, Wang B-C, Lindahl R, Nicholas H. 2001.Aldehyde dehydrogenase. Maintaining critical active site geometryat motif 8 in the class 3 enzyme. Eur J Biochem 268:722–726.

Ichihara K, Kusunose E, Noda Y, Kusunose M. 1986a. Someproperties of the fatty alcohol oxidation system and reconstitu-tion of microsomal oxidation activity in intestinal mucosa.Biochim Biophys Acta 878:412–418.

Ichihara K, Noda Y, Tanaka C, Kusunose M. 1986b. Purification ofaldehyde dehydrogenase reconstitutively active in fatty alcoholoxidation from rabbit intestinal microsomes. Biochim BiophysActa 878:419–425.

IJlst L, Oostheim W, van Werkhoven M, Willemsen MAAP,Wanders RJA. 1999. Molecular basis of Sjorgen-Larssonsyndrome: frequency of the 1297-1298 del GA and 943C4Tmutation in 29 patients. J Inher Metab Dis 22:319–321.

James PF, Zoeller RA. 1997. Isolation of animal cell mutantsdefective in long-chain fatty aldehyde dehydrogenase. Sensitiv-ity to fatty aldehydes and Schiff’s base modification ofphospholipids: implications for Sjogren-Larsson syndrome. J BiolChem 272:23532–23539.

Kelson TL, Secor M Jr, Rizzo WB. 1997. Human liver fatty aldehydedehydrogenase: microsomal localization, purification, and bio-chemical characterization. Biochim Biophys Acta 1335:99–110.

Kraus C, Braun-Quentin C, Ballhausen WG, Pfeiffer RA. 2000.RNA-based mutation screening in German families withSjogren-Larsson syndrome. Eur J Hum Genet 8:299–306.

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sjögren-larsson syndrome: diversity of mutations and polymorphisms in the fatty aldehyde...

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