Homocystinuria

What it means

An increased concentration of homocystine in the urine.

Homocystine is a disulfide derivate of homocysteine (a precursor of cysteine). Patients with homocystinuria have a clinical phenotype similar to that of patients affected by Marfan syndrome (pectus excavatum, dislocated lenses, etc). This term does not describe the disease entity, but rather the finding of an increased concentration of homocystine in urine, which can be easily detected by a sensitive test for disulphide compounds (the cyanide-nitroprusside reaction) and using chromatographic techniques. Homocystinuria can be caused by biochemical defects including cystathionine B-synthase deficiency, N5-methyltetrahydrofolate:homocystine methyltransferase deficiency, N5,10-methylentetrahydrofolate reductase deficiency, and methhylcobalamin deficiency.

Rare diseases that can present with this2

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category