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Nine Novel Mutations in Maturity-Onset Diabetes of the Young (MODY) Candidate Genes in 22 Spanish Families

Pediatric Diabetes Unit, Ramón y Cajal Hospital, University of Alcalá (R.B., J.C.M., H.C., M.A., C.M.), 28034 Madrid, Spain; and Foundation Jean Dausset-Centre d’Etude du Polymorphisme Humain (C.B.-C., V.M.), 75010 Paris, France

Address all correspondence and requests for reprints to: Raquel Barrio, M.D., Ph.D., Pediatric Diabetes Unit, Ramón y Cajal Hospital, Carretera Comenar Viejo Km 9.4, 28034 Madrid, Spain. E-mail: . rbarrio{at}hrc.insalud.es

Abstract

The aims of this study were to estimate the prevalence of major maturity-onset diabetes of the young (MODY) subtypes in Spanish MODY families and to analyze genotype-phenotype correlations. Twenty-two unrelated pediatric MODY patients and 97 relatives were screened for mutations in the coding region of the glucokinase (GCK), hepatic nuclear factor- HNF-1 and HNF4 genes using PCR-single strand conformation polymorphism and/or direct sequencing. In families carrying GCK mutations, the influence of genetic defects on fetal growth was investigated by comparing the birth weights of 32 offspring discordant for the mutations. Mutations in MODY genes were identified in 64% of the families. GCK/MODY2 mutations were the most frequently found, in 41%: seven novel (R369P, S411F, M298K, C252Y, Y108C, A188E, and S383L) and 2 already described mutations. Four pedigrees (18%) harbored mutations in the HNF-1/MODY3 gene, including a previously unreported change (R271G). One family (4%) carried a novel mutation in the HNF-4 gene (IVS5-2delA), representing the first report of a MODY1 pedigree in the Spanish population.

The age at diagnosis was prepubertal in MODY2 index patients and pubertal in MODY3 patients. Overt diabetes was rare in MODY2 and was invariably present in MODY3 index patients. Chronic complications of diabetes were absent in the MODY2 population and were present in more than 40% of all relatives of MODY3. Birth weight was lower in the presence of a GCK fetal mutation when the mutation was of paternal origin. The MODY1 patient was diagnosed at 15 yr of age. She developed intermittent microalbuminuria despite good metabolic control, and severe late-onset complications were common within her family.

Mutations in the GCK/MODY2 gene are the most common cause of MODY in our population as recruited from pediatric and adolescent index patients. The inheritance of GCK defects by the fetus results in a reduction of birth weight. Clinical expression of MODY3 and MODY1 mutations, the second and third groups of defects found, was more severe, including the frequent development of chronic complications.

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