A boy aged 4 years 7 months was evaluated because of severe developmental delay and failure to thrive. He had no recent illness. His spontaneous oral intake was poor (approximately 1260 kJ/day), although he had no vomiting or diarrhea. The full-term pregnancy and delivery were uneventful. Identified at age 1 week were cataracts, hypotonia, and cryptorchidism. Two fractured bones had been previously treated.
On physical examination, the boy was significantly developmentally delayed; he was unable to walk, stand, or crawl. His speech was delayed, although he appeared to hear and understand simple commands. His mother reported that he had once walked but had since lost this ability.
Measurements were as follows: weight, 8.46 kg (50th percentile for age 9 months); height, 80.5 cm (50th percentile for age 18 months); and head circumference, 51.5 cm (50th percentile for his age). He had bilateral cataracts, a prominent forehead, sparse hair, and normal