OBJECTIVES: The aim of this study was to take the molecular-genetic methods for detection of the most frequent mutations in patients suspected for achondroplasia (ACH) and hypochondroplasia (HCH) into the routine practice. BACKGROUND: Both disorders are usually caused by de novo gain-of-function type mutations in FGFR3 gene encoding the fi broblast growth factor receptor 3, which plays an important role in the metabolism of connective tissues. More than 99 % of ACH cases are caused by the glycine-to-arginine substitution at codon 380 and about 70 % of HCH cases result from the asparagine-to-lysine/-serine/-threonine substitutions at codon 540 in the consequence of the four different possible nucleotide changes occurred at the same codon. METHODS: Exons 10 and 13 of theFGFR3 gene were analysed by PCR-RFLP and sequencing analysis. The exon 13 sequencing was necessary for mutation type specifi cation. RESULTS: We confi rmed the diagnosis of ACH due to 1138G→A transition in 7 patients and we identifi ed 1620C→A transversion responsible for HCH in 2 patients. CONCLUSION: Due to serious limitations in recently used methods, we had to modify the molecular-genetic di-agnostics approach. We developed the reliable diagnostics and made it available for achondroplasia and hypochondroplasia suspected patients (Tab. 1, Ref. 5, Ref. 17). Text in PDF www.elis.sk.