Achondroplasia–hypochondroplasia complex in a newborn infant

We describe the case of an 8-month-old girl with achondroplasia-hypochondroplasia complex. The diagnosis was suggested antenatally when obstetrical ultrasonography at 27 weeks of gestation showed short limbs, small chest, and macrocephaly. The father has achondroplasia due to the common G1138A (G380R) mutation in the fibroblast growth factor receptor 3 (FGFR3) gene, while the mother has hypochondroplasia due to the C1620G (N450K) mutation in the FGFR3 gene. Neither had had genetic counseling or molecular testing prior to the pregnancy. Antenatal ultrasound study at 29 weeks of gestation showed a large head, very short limbs, and a small chest; the findings were more severe than in achondroplasia or hypochondroplasia alone. The patient was born by cesarean section at 37 weeks of gestation and had rhizomelic shortness of limbs with excess skin creases, large head, and small chest, diagnostic of achondroplasia. Radiographs showed shortness of the long bones and flaring of the metaphyses. She had mild hypoplasia of lungs. Molecular testing showed both the G1138A and the C1620G mutations in FGFR3, confirming the diagnosis of achondroplasia-hypochondroplasia complex. At 8 months, she has disproportionate shortness of the long bones and a large head with frontal bossing and a depressed nasal bridge. Her chest remains small, and she is on home oxygen at times of respiratory stress. She has a large gibbus. She is delayed in her motor development and has significant head lag. To our knowledge, there is only one previously published report of achondroplasia-hypochondroplasia complex.