GCK and MODY: In a study of 312 patients (162 boys and 150 girls) aged 3 months to 25 years with suspected MODY, 99 mutations in the GCK gene were identified among 129 probands and 77 relatives, 20 mutations in the HNF1A gene in 19 probands and 14 relatives, and 8 mutations in the HNF4A gene in 9 probands and 3 relatives.