Fragile X Syndrome and an Isodicentric XChromosome in a Woman With MultipleAnomalies, Developmental Delay, and NormalPubertal Development

Debra L. Freedenberg,1* Louise W. Gane,2 Carolyn S. Richards,3 Megan Lampe,2 Jennifer Hills,2Rebecca O’Connor,2 David Manchester,4 Annette Taylor,5 Flora Tassone,5 Dennis Hulseberg,6Randi J. Hagerman,2 and Shivanand R. Patil6

1Genetics Institute of Austin, Austin, Texas2Fragile X Treatment and Research Center, Child Development Unit, The Children’s Hospital, Denver, Colorado3Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas4Division of Genetic Services, The Children’s Hospital and University of Colorado Health Science Center,Denver, Colorado

5Kimball Genetics, Denver, Colorado6Division of Medical Genetics, University of Iowa Hospital and Clinics, Iowa City, Iowa

We report on an individual with develop-mental delays, short stature, skeletal abnor-malities, normal pubertal development, ex-pansion of the fragile X triplet repeat, aswell as an isodicentric X chromosome. S is a19-year-old woman who presented for evalu-ation of developmental delay. Pregnancywas complicated by a threatened miscar-riage. She was a healthy child with intellec-tual impairment noted in infancy. Althoughshe had global delays, speech was noted tobe disproportionately delayed with fewwords until age 3.5 years. Facial appearancewas consistent with fragile X syndrome. Ageof onset of menses was 11 years with normalbreast development. A maternal male sec-ond cousin had been identified with fragileX syndrome based on DNA studies. Themother of this child (S’s maternal firstcousin) and the grandfather (S’s maternaluncle) were both intellectually normal butwere identified as carrying triplet expan-sions in the premutation range. S’s motherhad some school difficulties but was notidentified as having global delays. Molecu-lar analysis of S’s fragile X alleles noted anexpansion of more than 400 CGG repeats inone allele. Routine cytogenetic studies of pe-ripheral blood noted the presence of anisodicentric X in 81of 86 cells scored. Five of

86 cells were noted to be 45,X. Cytogeneticfra(X) studies from peripheral blood showedthat the structurally normal chromosomehad the fragile site in approximately 16% ofthe cells. Analysis of maternal fragile X al-leles identified an allele with an expansionto ∼110 repeats. FMRP studies detected theexpression of the protein in 24% of cellsstudied. To our knowledge, this is the firstpatient reported with an isodicentric X andfragile X syndrome. Whereas her clinicalphenotype is suggestive of fragile X syn-drome, her skeletal abnormalities may rep-resent the presence of the isodicentric X.Treatment of S with 20 mg/day of Prozac im-proved her behavior. In the climate of costcontrol, this individual reinforces the rec-ommendation of obtaining chromosomes onindividuals with developmental delay evenwith a family history of fragile X syndrome.Am. J. Med. Genet. 85:197–201, 1999.© 1999 Wiley-Liss, Inc.

KEY WORDS: fragile X syndrome; isodicen-tric X; Turner phenotype

INTRODUCTIONFragile X syndrome is considered to be one of the

most common forms of mental retardation. The pheno-type of fragile X syndrome and the molecular and cy-togenetic aspects have been reported extensively. Wereport on an individual with the fragile X full mutationand an isodicentric X chromosome. Our patient ap-pears to have fragile X syndrome (developmental delay,normal pubertal development, facial and behavioral

*Correspondence to: Dr. Debra L. Freedenberg, Genetics Insti-tute of Austin, 711 W. 38th Street, Building F, Austin, TX 78705.E-mail: dfreeden@tcms.com

Received 22 August 1997; Accepted 7 February 1999

American Journal of Medical Genetics 85:197–201 (1999)

© 1999 Wiley-Liss, Inc.

characteristics) as well as skeletal findings suggestiveof Ullrich-Turner syndrome (short stature, short thirdand fourth metacarpals). To our knowledge, this is thefirst report of an individual with a structural abnor-mality of the X chromosome and fragile X syndrome.

CLINICAL HISTORY

S is a 19-year-old woman who presented for develop-mental delays. She was the 3.4-kg product of a termgestation born to a 31-year-old G2P1 woman. The preg-nancy was complicated by bleeding at 2-3 months ofgestation that was characterized as a “threatened mis-carriage.” She was born normally at term. Birth lengthwas 50.8 cm. At birth the child’s Apgar scores were9/10. She was noted to have mild motor delays at age 7months. She sat at 9 months, crawled at 11 months,and walked unassisted at 18 months. She did not havetwo-word sentences until 3.5 years, at which timesymptoms of attention deficit hyperactivity disorder(ADHD) became apparent. Hand flapping began at age18 months, and poor eye contact was noted at 3 years.At age 7 years she was noted to have a full scale IQ ofapproximately 69 by Stanford-Binet. At age 10 years aWISC-R evaluation noted a full scale performance ofapproximately 49 with poor abilities on verbal and per-formance scales. A repeat WISC-R at age 16 yearsnoted a verbal IQ of 59, performance IQ of 51, and a fullscale IQ of 51. Vineland Adaptive Behavior Scales atage 19 years noted communication skills at the 5.5-year level, daily living skills at the 10.3-year level, andsocialization at the 8.4-year level. Currently she isnoted to have global delays with verbal ability moreseverely affected. She is tactilely defensive and sensi-tive to noises.

Past medical history is significant in that she wasdescribed as a generally healthy child. She had PEtubes placed at age 4 years for recurrent otitis media.She had a tonsillectomy and adenoidectomy at 5 1⁄2years with repeat placement of PE tubes. Strabismus ofthe right eye was treated with patching in childhood;currently she has intermittent esotropia. S’s growthwas normal until the onset of menses at age 11 years,after which her growth decelerated. She currently re-mains on birth control pills for regulation of mensesafter a history of menorrhagia. She underwent a trial of20 mg of Ritalint per day for apparent ADHD in thirdgrade. However, no improvement was noted, and Ri-talint was discontinued. She developed anxiety-outburst behavior, impulsivity, and became sociallyavoidant in adolescence.

Family History

A male maternal second cousin was identified withfragile X syndrome on the basis of DNA studies (>230CGG repeats in the FMR1 gene (analysis was per-formed by an outside laboratory)) and developmentaldelays. His maternal grandfather (S’s maternal uncle)did not have intellectual deficits and was identified asa having ∼120 CGG repeats (premutation range) in theFMR1 gene. S’s mother described herself as havinglearning disabilities and had difficulty in reading andmath throughout school. She completed high school ina regular classroom but was unable to complete collegelevel courses. S’s maternal grandmother was said tohave premature ovarian failure at age 35 and severedepression resulting in suicide. Another maternaluncle to S was noted to be hearing impaired (diagnosedat age 1 year). See pedigree (Fig. 1) for further familyhistory.

Fig. 1. Pedigree of the family. , fragile X and isodic X; , fragile X syndrome; , obligate carrier fragile X premutation; , premutation fragileX (transmitting male); , premutation fragile X (heterozygote); , hearing impaired. Numbers refer to CGG repeat number in FMR1 gene. *, DNAanalysis by outside lab.

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Physical Examination

S’s height was 147 cm ((Fig. 2) <5th centile for an18-year-old woman, 50% for an 11-year-old) withweight between 75–90th centile for age and an OFC of53 cm (within one standard deviation for age). Armspan was 140 cm. Lower segment was 67.5 cm. Upperto lower segment ratio was 1.18 (above normal rangefor age). Her left arm measured 29 cm, the forearmmeasured 24.75 cm. Total hand length was 17.5 cmwith a middle finger length of 8.5 cm. The thigh mea-sured 33 cm, and the leg 44 cm. She had apparentprognathism, narrow high arched palate, cupped ears,and small carious teeth (Fig. 2). Her neck was notbroad and no webbing was noted. A slightly low poste-rior hairline was also noted. She did not have cubitusvalgus. Upper and lower limbs appeared to have me-somelic shortness. Metacarpal-phalangial extensionwas limited to 90 degrees. Thumbs were hyperexten-sible. She had a hyperkerototic region on her lateralthigh and a single small 3 × 4 cm irregular cafe-au-laitspot over the left lateral tibia. Breast development wasTanner 4 with normal secondary sexual development.She was dysarthric with perseverative speech and pooreye contact. The remainder of the physical and neuro-logical findings was normal.

Laboratory Evaluation

Thyroid function was normal. A skeletal surveynoted a bilateral Madelung deformity with shortness of

the radii and ulnae and short 4th and 5th metacarpals(Fig. 3). In addition, there was a mild irregularity of theend plates of the thoracic vertebrae, and there was an-terior wedging of the 12th thoracic vertebra.

CYTOGENETIC STUDIES

Although the fragile X mutation was known to beinherited in the patient’s family, peripheral blood wasobtained for routine cytogenetic analysis and for FMR1mutation studies. Five (5/86 4 6%) cells were found tobe 45,X. The remaining 81 (81/86 4 94%) had 46 chro-mosomes, including an isodicentric X. Of the 86 cells,56 were from cultures stressed for the induction of thefragile X. Nine of the 56 cells examined (16%) had thefra(X)(q27.3) and were from a clone with 46 chromo-somes (Fig. 4). Therefore, the patient’s karyotype des-ignation was 46,fra(X)(q27.3),idic(X)(p21.3)[81]/45,fra(X)(q27.3)[5]. Part of the blood was used for con-current FMR1 studies.

MOLECULAR STUDIES

Analysis of genomic DNA from S by polymerasechain reaction using primers flanking the CGG repeatregion of the FMR1 gene detected an allele of 29 CGGrepeats (normal). Southern analysis by routine meth-ods (EcoR1 and EcoR1 + BSSH II) detected an addi-tional allele of approximately 400 CGG repeats (fullmutation). Southern methylation data noted hyper-

Fig. 2. The patient with cupped ears, apparent prognathism, and high arched palate consistent with fragile X syndrome. She is also noted to havemesomelic shortness of limbs.

Fragile X Syndrome and Isodicentric X 199

methylation, as would be predicted from nonrandom Xinactivation of a structurally abnormal X chromosome(isodicentric X), and a structurally normal X chromo-some with an inactive FMR1 gene caused by tripletexpansion.

The cytogenetic data clearly indicate that the struc-turally normal chromosome carries the fragile X muta-tion. Thus, the allele size of 29 presumably representstwo identical alleles on the isodicentric X chromosome.S’s genotype is inferred to be 29/29/∼400.

S’s mother had one allele of 31 CGG repeats (normal)and a second of ∼110 CGG repeats (premutation) iden-tifying her as a heterozygote for the premutation. S’sfather had a single allele of 29 CGG repeats (normal).

S’s maternal uncle had approximately 120 CGG re-peats (premutation). S’s maternal male second cousinwas noted to have an allele of >230 CGG repeats (fullmutation) and was clinically symptomatic.

PROTEIN ANALYSIS

Expression of FMRP was noted in 24% of 200 lym-phocytes scored. The methods of Devys and Willemsenet al. were used for this study. This low level of expres-sion is consistent with individuals symptomatic forfragile X syndrome.

TREATMENT

The anxiety outburst behavior, impulsivity, and so-cial avoidance experienced by S were treated with 20mg of fluoxetine (Prozact) taken once daily. S and herparents report that while on the prescribed medicationshe has had less anxiety and increased sociability andself-sufficiency. This has resulted in improved self-esteem and quality of life for S.

DISCUSSION

To our knowledge, this is the first report of an indi-vidual with a structurally abnormal X chromosome(isodicentric Xp21.3) and a structurally intact X chro-mosome carrying the fragile X mutation. Her develop-mental delay, cupped ears, apparent prognathism,high arched palate, and hyperextensible joints aremanifestations that are associated with fragile X syn-drome. In the presence of a structurally abnormal Xchromosome (isodicentric X), nonrandom X inactiva-tion would be postulated. Because her structurally nor-mal X chromosome carries the fragile X mutation shewould have no active FMR1 gene, explaining the clini-cal signs similar to those of males with fragile X syn-drome. The presence of DNA hypermethylation in theregion of the FMR1 gene provides evidence of inactiva-tion of the FMR1 gene.

Most individuals with an isodicentric X and low-levelmosaicisim for 45,X (∼6%) present with an Ullrich-Turner like phenotype. S’s skeletal findings of shortstature, short metacarpals, and a Madelung-like defor-mity may be a manifestation of the isodicentric X. Al-though Madelung deformity, mesomelic shortness, andshort stature are present in dyschondrosteosis, it isdifficult to interpret these findings in the presence ofan isodicentric X chromosome and a 45,X cell line. AnX-linked pseudoautosomal form of dyschondrosteosishas been reported, and it is possible that because ofnonrandom X inactivation, a second mutation in theregion of Xp might be expressed from the chromosomecarrying the FMR1 mutation. The different clinical

Fig. 4. GTG-banded fragile X chromosome (left, arrow) and isodicen-tric X chromosome (right) along with schematic representation to illus-trate the breakpoint (arrow).

Fig. 3. Skeletal survey notes radiograph of right forearm, wrist, andhand with Madelung, shortness of ulna and radius bilaterally, and shortfourth and fifth metacarpals.

200 Freedenberg et al.

presentation may reflect a distal breakpoint of theisodicentric X and the influence of the fragile X muta-tion.

This patient provides an interesting observation re-garding the isodicentric X chromosome. The single mo-lecular marker suggests that the paternal X is involvedin the formation of the isodicentric X. The cytogeneticand molecular studies have localized the fragile X mu-tation to the structurally normal maternally derivedchromosome. The molecular data detected only onenormal allele (29 CGG repeats) and a mutant allelewith an expansion to ∼400 repeats. The allele of 29repeats presumably represents two identical alleles onthe isodicentric X chromosome and matches the size ofthe paternal allele. Analysis of further molecularmarkers on the isodicentric X chromosome may helpelucidate the mechanism of formation.

This patient presented with a family history of frag-ile X syndrome. If only DNA diagnostics had been per-formed, important clinical information would havebeen missed. These findings reinforce the recommen-dation of performing a routine chromosome analysis onall individuals with developmental delays.

ACKNOWLEDGMENTS

We thank Don Kronenberg for computer assistance.

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