Cystathioninuria, also called cystathionase deficiency, is an autosomal recessive metabolic disorder. It is characterized by an abnormal accumulation of plasma cystathionine leading to excess cystathionine in the urine. Hereditary cystathioninuria is associated with the reduced activity of the enzyme cystathionine gamma-lyase. It is considered a biochemical anomaly. This is because it associated with a wide range of diseases and its inconsistency. Cystathionase catalyzes cystathionine to cysteine and α-ketobutyrate. Cysteine is an essential amino acid and its conversion from cystathionine occurs in the trans-sulfuration pathway. The availability of cysteine is necessary for the synthesis of an important anti-oxidant, glutathione. Cystathionase has a co-enzyme, pyridoxal phosphate, which is the active form the vitamin B6. This means that vitamin B6 is essential for the function of cystathionase. Cystathioninuria can be broken down into two main categories. Primary cystathioninuria is caused by the recessive inherited deficiency of cystathionase enzyme. Secondary cystathioninuria is described by non-genetic conditions of excess cystathionine. Secondary cystathioninuria includes temporary excess cystathionine of premature infants, severe generalized liver damage, thyrotoxicosis, hepatoblastoma, or neuroblastoma. Cases of secondary cystathioninuria are not responsive to vitamin B6 administration. Types
Under primary cystathioninuria, the inherited mutation of CTH gene, there are two forms. There is vitamin B6 – unresponsive and vitamin B6 – responsive cystathioninuria. The vitamin B6 – unresponsive form is thought to be from a lack of the synthesis of cystathionase. This means that the mutation in CTH from this form of cystathioninuria, results in the absence of cystathionase.
Two missense mutations were also found, mainly in exon 2 and exon 7. In addition, a common non-synonymous single nucleotide polymorphism in exon 12 was also identified. The presence of various CTH mutations is consistent with the various categories associated with cystathioninuria. Diagnosis
The main way to diagnosis cystathioninuria is simply through increased urinary excretion of cystathionine. In some cases, a genetic test is employed. Treatment
The treatment, if any is available, varies depending on the category of cystathioninuria a patient has. The vitamin B6 – responsive form is best treated by an increased consumption of vitamin B6. This increased consumption helps with cystathionases altered ability to bind to the active form of vitamin B6. References


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