Thelansis

  Homocystinuria, caused by cystathionine β-synthase deficiency, is a rare inherited disorder involving methionine metabolism. Impaired synthesis of cystathionine leads to accumulation of homocysteine that affects several organ systems leading to abnormalities in the skeletal, cardiovascular, ophthalmic, and central nervous systems. The primary defect is a marked reduction in the activity of the critical enzyme for transsulfuration, cystathionine β-synthase (CBS). It is biochemically characterized by elevated methionine and total homocysteine and contractions in cystathionine, the immediate product of CBS, and cysteine. Other defects in the methionine metabolic cycle that result in homocystinuria are remethylation defects in which the conversion of homocysteine back to methionine is impaired. These defects produce reduced rather than increased methionine and increased homocysteine and may also be associated with an increase in methylmalonic acid. With one exception, methylenetetrah...