Abstract: Objective To explore the clinical and genetic features of molybdenum cofactor deficiency. Method The clinical data of molybdenum cofactor deficiency in a patient was retrospectively analyzed. Result A 6 -month-old girl was born with no abnormalities. However, she had feeding difficulties and convulsion immediately after birth, and gradually developed microcephaly and spastic tetraplegia, etc. Whole exome sequencing showed compound heterozygous variation of c. 473 T>G (p.Leu 158 *) and c. 472 _ 477 del (p.Leu 158 _Lys 159 del) in MOCS2 gene, which were inherited from her father and mother respectively. According to the ACMG guidelines, the c. 473 T>G variation was classified as pathogenic, while the c. 472 _ 477 del variation was classified as likely pathogenic. Conclusion The child was diagnosed with molybdenum cofactor deficiency caused by heterozygous variation in the MOCS 2 gene.

Key words: r deficiency caused by heterozygous variation in the MOCS 2 gene.