CYSTATHIONINURIA is a rare inborn error of metabolism which was first described in 1959 in a female imbecile who died at the age of 64.1 Her urinary excretion of cystathionine increased when she was fed methionine, and at autopsy large amounts of cystathionine were found in her brain.2 One of her brothers and his son, both normal in intelligence, excreted cystathionine in their urine in amounts greater than normal but less than the patient.
In 1963 a second patient with cystathioninuria, a 44-year-old man with acromegaly, was reported.3 He had a full-scale IQ of 100, various, probably unrelated, minor congenital abnormalities, and was deaf. His blood and cerebrospinal fluid (CSF) levels of cystathionine were elevated, and his sister, normal in other respects, excreted about half as much cystathionine as her affected brother. Frimpter et al, who investigated this patient, contributed a most significant observation. When their subject