Homocystinuria is a rare autosomal recessive disorder of amino acid metabolism. Classic (type I) homocystinuria is the most common type and occurs as a consequence of a deficiency of cystathionine-bsynthase, producing increased blood and urine homocysteine. The authors report a 15-year-old Thai male who presented with generalized tonic-clonic seizures from superior sagittal sinus thrombosis, bilateral downward subluxation of ocular lenses (ectopia lentis), Marfanoid habitus, osteoporosis, attention deficit and hyperactivity disorder. Urine metabolic screening was positive for cyanide nitroprusside test. Levels of plasma homocysteine and methionine were elevated. The clinical and laboratory findings in this case are consistent with the diagnosis of çtype Ié or çclassical homocystinuriaé. The treatment was started with a low methionine diet, vitamin B6 or pyridoxine, folic acid, anticonvulsants, antithrombotic treatment and calcium supplementation. Genetic counseling was provided to the family with the recurrent risk of 25%. Definite diagnosis by enzyme assay or mutation analysis and also prenatal diagnosis are not established in Thailand.

Keywords: Homocystinuria, Homocystinemia, Homocysteine, Cystathionine β-synthase