Prenatal diagnosis of hypochondroplasia: report of two cases.

Hypochondroplasia (HCH) is an autosomal dominant skeletal dysplasia characterized by short extremities, short stature and lumbar lordosis, usually exhibiting a phenotype similar to but milder than achondroplasia (ACH). Mutations in the fibroblast growth factor receptor 3 (FGFR3) gene are present in a significant proportion of HCH patients. Reports of prenatal diagnosis of HCH are very rare and the phenotype/genotype correlation in these patients is poor. Here we present two sporadic cases with second trimester ultrasound findings consistent with a diagnosis of a non-lethal skeletal dysplasia. Ultrasound evaluation after 23 weeks of gestation showed a decreased rate of development of the femora (femur length <fifth centile), while biparietal diameter, abdominal circumference, and foot length were within normal limits. Femur length/foot and femur length/abdominal circumference ratios were <0.87 and <0.18, respectively. Prenatal cytogenetic and molecular genetic analysis was performed. Karyotype was normal and FGFR3 G380R mutation characteristic of ACH was excluded in both fetuses. Molecular genetic analysis carried out retrospectively revealed that both fetuses were heterozygous for the C1620A mutation resulting in N540K substitution in FGFR3, the most common mutation in HCH. We conclude that the combination of ultrasound and molecular genetic approach is helpful for establishing an accurate diagnosis of HCH in utero and subsequently for appropriate genetic counseling and perinatal management. 2006 Wiley-Liss, Inc.