Editor—The study of achondroplasia, the most frequent skeletal dysplasia in man, has contributed several important insights into both developmental biology and human genetics, such as the recognition of the paternal age effect for dominant mutations,1 2 the first indication of the importance of FGFR molecules in growth and development,3 and the identification of the nucleotide with the highest mutation rate known so far in man, nucleotide 1138 of the FGFR3gene.4 Most cases of achondroplasia are associated with the g→a transition at nucleotide 1138 ofFGFR3.4

In spite of the frequency of achondroplasia, the birth of two or more children with achondroplasia to unaffected parents is surprisingly rare, with only a few examples published.5 6 One instance of half sibs with achondroplasia born …