Molybdenum cofactor is essential for the activity of multiple
enzymes including
xanthine dehydrogenase.
Molybdenum cofactor deficiencies are rare
inborn errors of metabolism. Clinically, they present with intractable
seizures, axial
hypotonia, and
hyperekplexia. They further develop cerebral
atrophy,
microcephaly, global developmental delay and
ectopia lentis. We report a 5-year-old female with clinically, biochemically and genetically confirmed
molybdenum cofactor deficiency type B due to compound heterozygous pathogenic variants in the
molybdenum cofactor synthesis 2 gene found on whole exome sequencing. The
xanthine stones were a key clue towards diagnosis. No mutation was detected in XDH gene. Implementation of a low-
purine diet, urine alkalization and hydration lead to a near complete decrease in stone burden. The patient received
pyridoxine supplementation with improvement in energy levels and attentiveness. Despite reports of high mortality at a young age, our patient was 9 years old at the time of this writing.
Molybdenum cofactor deficiencies should be considered in neonates with early-onset
seizures,
hypotonia, and feeding difficulties. Screening with serum
uric acid levels and empiric treatment may be considered while awaiting genetic results.