Homocystinuria is an inherited metabolic disorder characterised by an increased blood and urine concentration of homocysteine and its metabolites. The clinical features of homocystinuria include myopia, ectopia lentis, skeletal anomalies and intellectual disability. The classic form of homocystinuria is caused by homozygous or compound heterozygous mutation in the CBS gene which encode an enzyme called cystathionine beta-synthase - an important component in the chemical pathway that coverts homocysteine to cystathionine.