Homozygous N540K hypochondroplasia--first report: radiological and clinical features.

We describe a 16-month-old male with N540K homozygous mutation in the FGFR3 gene who showed a more severe phenotype than hypochondroplasia (HCH). To our knowledge, a homozygous state for this mutation causing HCH has not been reported before. The clinical and radiological characteristics of our patient represent an intermediate condition between achondroplasia and achondroplasia/hypochondroplasia compound heterozygosity. This case represents a new expression of FGFR3 spectrum and it is of considerable importance for the genetic counseling in cases where both parents are affected with HCH.