Homocystinuria

A rare autosomal (from both parents) genetic condition in which the person is unable to metabolize the amino acid homocystine because they lack an enzyme which breaks it down.  As a result, there is a toxic buildup of by-products which causes a number of symptoms including tall thin build with long limbs, spidery fingers, high arches, knock knees, spinal curvature, osteoporosis, mental retardation, and behavioral and psychiatric conditions.