Cystathioninuria is an autosomal recessive inborn error of metabolism characterized by an excess urinary excretion of cystathionine. Relative to most other metabolic disorders, cystathioninuria is considered to be a benign biochemical anomaly, since there are no striking pathological features. However, there have been reports of the disease being associated with mental deficiency. In most cases, the disorder is pyridoxine-dependent, although rare non-dependent cases have also been reported. In the pyridoxine-dependent cases, a dramatic response can be seen to the administration of vitamin B6.
Cystathioninuria is associated with mutations in CTH gene, which encodes cystathionine gamma-lyase enzyme involved in the normal metabolism of methionine. Deficiency of this enzyme leads to abnormal accumulation of cystathionine in the body, which is excreted through the urine. Since pyridoxone functions as a co-factor for cystathionine gamma-lyase enzyme, the same effect comes about with a congenital or acquired deficiency of vitamin B6.
Yadav et al. (1992) performed a quatitative HPLC analysis to detect any cases of aminoacidopathies among a group of 187 institutionalized mentally retarded patients (118 females) in Kuwait, during a 4-year period. One patient (0.23%) was detected to have cystathioninuria.