In this pedigree, all the three affected patients (III:2, III:3 and III:4) were found to harbor both of the two missense mutations in CBS. The patients in this family were diagnosed as homocystinuria based on detection of elevated blood homocysteine, and diagnosis of skeletal deformities, mental retardation and ectopialentis. The gene discussed is CBS; the disease is homocystinuria.