Hypochondroplasia is a milder skeletal dysplasia than achondroplasia, although the conditions may overlap (both clinically and molecularly). For example, the same
G380R(1138G^A) mutation in FGFR3 is found in 97% of cases of achondroplasia and 5% of cases of hypochondroplasia. FGFR3 mutations account for 50% to 75% of cases of hypochondroplasia. The remaining cases do not currently appear to have FGFR mutations, and thus the possibility of genetic heterogeneity must be considered. Two different point mutations at codon 540 account for up to 70% of hypochondroplasia alleles.
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