Arakawa's syndrome II

Arakawa's syndrome II is an inborn error of metabolism, a genetic disorder that causes a deficiency of the enzyme tetrahydrofolate-methyltransferase; affected individuals cannot properly metabolize methylcobalamin, a type of Vitamin B12.

It is also called Methionine synthase deficiency, Tetrahydrofolate-methyltransferase deficiency syndrome, and N5-methylhomocysteine transferase deficiency.

Presentation
This disorder causes neurological problems, including mental retardation, brain atrophy and ventricular dilation, myoclonus, hypotonia, and epilepsy.

It is also associated with growth retardation, megaloblastic anemia, pectus excavatum, scoliosis, vomiting, diarrhea, and hepatosplenomegaly. Inheritance is autosomal dominant.

Eponym
It is often called "Arakawa syndrome 2" after Tsuneo Arakawa; in this context, "Arakawa syndrome 1" refers to Glutamate formiminotransferase deficiency.