Homocystinuria is an autosomal recessive disorder that is caused by an overaccumulation of homocysteine in the body. It’s caused by defects in cystathionine synthase, methionine synthase, vitamin B6, and MTHFR. Clinical manifestations of homocystinuria include marfanoid habitus and kyphosis, caused by defects in collagen cross-linking; ocular abnormalities such as lens subluxation; developmental delay; thrombosis and atherosclerosis; and finally hypopigmented skin and hair.