Germline mosaicism in achondroplasia detected in sperm DNA of the father of three affected sibs.

We describe a sib recurrence for achondroplasia with parents of average stature. The three sibs shared the paternal allele and all carried the same causal mutation in the fibroblast growth factor receptor 3 gene (FGFR3): G > A nt1138 (Gly380Arg). We were able to identify this mutation on sperm DNA confirming paternal germinal mosaicism. Our family shows that a more precise definition of the recurrence risk is feasible using this approach, based on a single DNA test, which could be offered in selected cases.