Homocystinuria or HCU is an inherited disorder of the metabolism of the amino acid methionine due to a deficiency of cystathionine beta synthase or methionine synthase. It is an inherited autosomal recessive trait, which means a child needs to inherit a copy of the defective gene from both parents to be affected. Symptoms of homocystinuria can also be caused by a deficiency of vitamins B6, B12, or folate. Signs and symptoms
This defect leads to a multi-systemic disorder of the connective tissue, muscles, central nervous system (CNS), and cardiovascular system. Homocystinuria represents a group of hereditary metabolic disorders characterized by an accumulation of the amino acid homocysteine in the serum and an increased excretion of homocysteine in the urine. Infants appear to be normal and early symptoms, if any are present, are vague.Signs and symptoms of homocystinuria that may be seen include the following:

Cause
It is usually caused by the deficiency of the enzyme cystathionine beta synthase, mutations of other related enzymes such as methionine synthase, or the deficiency of folic acid, vitamin B12 and/or pyridoxine (vitamin B6). Diagnosis
The term homocystinuria describes an increased excretion of the thiol amino acid homocysteine in urine (and incidentally, also an increased concentration in plasma). The source of this increase may be one of many metabolic factors, only one of which is CBS deficiency. Others include the re-methylation defects (cobalamin defects, methionine synthase deficiency, MTHFR) and vitamin deficiencies including riboflavin (vitamin B2), pyridoxal phosphate (vitamin B6), folate (vitamin B9), and cobalamin (vitamin B12).
Ketoconazole can also be used for type I under certain conditions.The component diseases are managed as usual; the challenge is to detect the possibility of any of the syndromes and to anticipate other manifestations. For example, in a person with known type 2 autoimmune polyendocrine syndrome but no features of Addisons disease, regular screening for antibodies against 21-hydroxylase may prompt early intervention and hydrocortisone replacement to prevent characteristic crises

See also
Immunosuppression

References
Further reading
Improda, Nicola; Capalbo, Donatella; Cirillo, Emilia; Cerbone, Manuela; Esposito, Andrea; Pignata, Claudio; Salerno, Mariacarolina (1 November 2014). "Cutaneous vasculitis in patients with autoimmune polyendocrine syndrome type 1: report of a case and brief review of the literature". BMC Pediatrics. 14: 272. doi:10.1186/1471-2431-14-272. ISSN 1471-2431. PMC 4286916. PMID 25361846. Shoenfeld, Yehuda; Cervera, Ricard; Gershwin, M. Eric (2008). Diagnostic Criteria in Autoimmune Diseases. Springer Science & Business Media. ISBN 9781603272858. External links
Diseases Database (DDB): 29690
PubMed