Abstract
Background To describe the genotype-phenotype dissociation in two Taiwanese patients with molybdenum
cofactor deficiency (MoCoD) caused by MOCS2 gene mutations.
Patient Description Patient 1 exhibited early-onset neurological symptoms soon after birth, followed
by subsequent myoclonic seizures and movement disorder. The brain magnetic resonance
imaging (MRI) showed diffuse brain injury with cystic encephalomalacia along with
bilateral globus pallidi involvement, hypoplasia of corpus callosum, and cerebellar
atrophy. Patient 2 had a mild phenotype with prominent movement disorder after intercurrent
illness, and the brain MRI showed selective injury of the bilateral globus pallidi
and the cerebellum. Both patients had markedly low levels of plasma uric acid and
harbored the same MOCS2 homozygous c.16C > T mutation. Patient 1 showed chronic regression of developmental
milestones and died of respiratory failure at the age of 8 years, whereas patient
2 demonstrated improvement in motor function.
Conclusion Genotype-phenotype dissociation could be noted in patients with MoCoD due to MOCS2 mutation. Patients with neonatal seizures, developmental delay, movement disorder,
and motor regression after an illness, as well as focal or bilateral involvement of
the globus pallidi on the neuroimages, should undergo biochemical testing of plasma
uric acid. A pronounced plasma uric acid level is a good indicator of MoCoD. Early
diagnosis can allow early provision of adequate genetic counseling.
Keywords
brain MRI - globus pallidus - hypouricemia -
MOCS2 gene - molybdenum cofactor deficiency
