[Molybdenum cofactor deficiency caused by MOCS1 gene mutation: a case report].

A boy attended the hospital at the age of 1 month due to left hand tremor for 1 week. A blood test showed a reduction in serum uric acid and a cranial MRI showed encephalomalacia, atrophy, and cystic changes. The boy had microcephalus, unusual facial features (long face, long forehead, protruded forehead, long philtrum, low nasal bridge, facial swelling, and thick lower lip), hypertonia of lower extremities, and severe global developmental delay. Whole-exome sequencing performed for the boy detected a homozygous mutation, c.217C > T(p.R73W), in the MOCS1 gene, which came from his parents and was determined as "possibly pathogenic". The boy was diagnosed with molybdenum cofactor deficiency type A based on clinical manifestations and gene test results. This disease is reported for the first time in China.