HUMAN MUTATION Supplement l:S72-S73 (1998)

MUTATION Rv BRIEF

Beatriz Siinchez,’* Guillermo Antiiiolo,’ Elena Navarro,’ Miguel A. Jap~jn ,~ Antonio F. C ~ n d e , ~ Ricardo Astorga,’ and Salud Bornego’* ’Unldad de Genetica Midica, Hospital Universitario Virgen del Rocio, 41013 Sevilla, Spain 2Servicio de Endocrinologia, Hospital Universitario Vtrgen del Rocio, 4 I01 3 Sevilla, Spain 3Departumento de Anatomfa, Hospital Universitario Virgen del Rocio, 41013 Sevilla, Spain

Communicated by Michel Goossens

Multiple endocrine neoplasia type 2A (MEN 2A) is a dominantly inherited cancer syndrome charac- terized by medullary thyroid carcinoma (MTC), pheochromocytoma (pheo), and/or parathyroid hy- perplasia (Schimke et al., 1984). Elevation of cal- citonin levels after provocative stimulation with pentagastrin and/or CaZ+ is a sensitive indicator of hyperplasia of the thyroidal C-cells, which in MEN 2A patients may indicate a developing tu- mor (Wells et al., 1978). In most MEN 2A fami- lies, missense mutations involve one of the five cysteine residues in the extracellular cysteine-rich domain in exons 10 and 11 of the RET proto-on- cogene (Mulligan et al., 1994). We report theRET mutations responsible for the disease in seven Spanish MEN 2A families.

Mutations in exon 11 of the RET proto-oncogene were analysed in 73 individuals (25 affected and 48 at-risk individuals) using the method described else- where (McMahon et al., 1994). The mutation analy- sis results were confirmed by direct sequencing of exon 11. The seven MEN 2A families studied had mutations in codon 634 (TGC), which encodes a cysteine residue in the extracellular domain of RET, whereas the 50 control individuals tested had no mutation. The distribution of mutations is presented in Table 1. Direct mutation analysis confirmed that an individual with borderline calcitonin test and an- other with elevated urinary catecholamines and am- biguous adrenal image do not carry the mutation present in their families. Other two individuals who showed borderline calcitonin tests were confirmed as carriers of the familial mutation. In one family, a woman was treated by thyroidectomy on the basis of positive plasma calcitonin stimulation test. Pathologic studies were consistent with C-cell hyperplasia. DNA analysis showed that she does not carry the G+A change present in affected members of the family.

0 1 9 9 8 WILEY-LISS, INC.

This finding provides further evidence for the occur- rence of C-cell hyperplasia in thyroid glands of indi- viduals with a variety of disorders different to MEN 2A (Scopsi et al., 1991).

The use of genetic testing have raised some ques- tions regarding the role of biochemical screening pro- cedures in the diagnosis of hereditary MTC and related diseases. PCR and restriction enzyme analysis have allowed us to detect the causative mutation in 100% of MEN 2A families and sup- ports the idea that this test is an excellent method for identifying individuals as carriers or noncarriers in MEN 2A families in our population. Unlike bio- chemical screening, DNA analysis allows unam- biguous identification of gene carriers, avoiding possible errors and unnecessary surgery resulting from false positive results.

In conclusion, the identification ofRET mutation carriers allows earlier and accurate detection of at- risk subjects and the exclusion of noncarrier individu- als from further biochemical tests in MEN 2A families. In view of its predictive value and greater sensitivity, direct DNA mutation testing is the pre- ferred approach for diagnosis.

ACKNOWLEDGMENTS

This work was supported by grant 95/1667 from the Fondo de Investigaciones Sanitarias (Spain). B.S. is the recipient of the research grant.

Received 15 February 1996; accepted 19 May 1996. *Corresuondence to: S. Borreoo. M.D.. Unidad de Genetica

Medica, Hoipital Universitario “Virggn del Rocio,” Avda.M.Siurot s/n, 41013 Sevilla, Spain. Fax: 34-5-424-8111.

Contract grant sponsor: Fondo de Investigaciones Sanitarias; Con- tract grant number: 95/1667.

CYS 634 MUTATIONS IN SPANISH FAMILIES S73

TABLE 1. Detection and Distribution of Missense Mutations Identified in RET Codon 634 in Seven Spanish MEN 2A Families

Number of Amino families Enzyme

Codon 634 acid with this site mutations change mutation created TGC+TAC C ys+Tyr 5 Rsal TGC-SGC Cys+Arg 2 Hhal TGC+GGC Cys+Gly 0 HaeIII TGC+AGC Cys-tSer 0 DdeI Total 717

Restriction fragments Extra bands

(bp), normal generated sequence by mutation 140,28 76,64 157,ll 101,56 161,7 95,66 152,16 81.71

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