Radiological clues to the early diagnosis of hypochondroplasia in the neonatal period: report of two patients.

Hypochondroplasia (HCH) is the mildest phenotype among fibroblast growth factor receptor 3 (FGFR3)-associated skeletal dysplasias. Affected individuals usually presents with mild short stature in preschool age. It was uncommon that a diagnosis of HCH is made in young affected children. Recently, however, prenatal ultrasound (US) has increased likelihood of detecting in utero mild short limbs. There have been a few reports on the early diagnosis of HCH in the neonatal period preceded by a suspicion of skeletal dysplasia on fetal US. However, the proper diagnosis of HCH is hampered by absence of the radiological criteria relevant to age, particularly those in the neonatal period. We report on the clinical and radiological findings in two HCH children with a FGFR3 mutation. In both children, fetal US showed short femora and relatively increased biparietal diameter (BPD). However, postnatal assessment failed to make a specific diagnosis in the neonatal period. The correct diagnosis of HCH was accomplished by reassessment after exacerbation of postnatal short stature. In retrospective radiological review, the radiological findings relevant to HCH were discernible more easily in the neonatal period than at age of 3 years.