Context: Maturity Onset Diabetes of the Young (MODY) type 5 has been described as the association of early-onset diabetes and renal disease. Actually, MODY5 encompasses multiple phenotypes including non-diabetic progressive renal failure, kidney and genital tract malformations, atypical familial hyperuricemic nephropathy, pancreas atrophy and liver test abnormalities. The occurrence of MODY5 has been associated with various molecular abnormalities of TCF2, including missense, nonsense, small insertion/deletions and splice site mutations as well as large genomic deletions or single exonic deletion of TCF2.

Design: Using quantitative multiplex PCR amplification of short fluorescent fragments (QMPSF), we have analyzed the TCF2 gene in a French family of which three relatives presented a MODY5 phenotype. The proband had an extended clinical phenotype including hyperuricemic nephropathy and early gout, chronic renal failure, renal morphological abnormalities, abnormal liver tests, and diabetes. His son had almost no clinical expression of the disease whereas his grandson had a restricted but severe renal phenotype present from birth.

Results: We show that a duplication of the exon 5 of TCF2 is responsible for the MODY5 phenotypes in this family.

Conclusions: Thus we describe a novel molecular mechanism that may be responsible for MODY5 and we emphasize the wide intrafamilial variability of MODY5 expressivity. These observations suggest that the diagnosis of MODY5 may be raised even in subjects with partial phenotypes. They also confirm that QMPSF analysis should be the first step of genetic screening in patients with a MODY5 phenotype.