Perry et al. (1967) described 2 unrelated children with a progressive neurologic disorder characterized by severe mental defect and myoclonic seizures. Both excreted carnosine (see 609064) in the urine, even when all source of the dipeptide was excluded ... Perry et al. (1967) described 2 unrelated children with a progressive neurologic disorder characterized by severe mental defect and myoclonic seizures. Both excreted carnosine (see 609064) in the urine, even when all source of the dipeptide was excluded from the diet. Both had unusually high concentrations of homocarnosine in the cerebrospinal fluid. When fed a dietary source of anserine, the children excreted anserine in the urine but not its hydrolysis product, methylhistidine. Perry et al. (1967) suggested that one, and perhaps both, had a defect in carnosinase (see 609064) activity. One child, of German and Dutch ancestry, was the offspring of first-cousin parents. The other child was of Chinese ancestry. Perry et al. (1968) found that the enzyme of normal human serum that hydrolyzes the dipeptides carnosine and anserine into their constituent amino acids was almost absent in the 2 patients. No comment was made on the level of enzyme in the parents. Carnosine is a dipeptide of alanine and histidine. Scriver et al. (1968) commented on the possible relationship of the mental retardation that occurs with hyper-beta-carnosinemia and phenylketonuria (261600). In the case of the affected Dutch child reported by Heeswijk et al. (1969), the parents were consanguineous and showed decreased serum carnosinase activity. Terplan and Cares (1972) reported another family with this rare anomaly. Two brothers, aged 7 and 4, had died. A 6-year-old sister was normal but had chemical changes. The parents have low carnosinase activity. Autopsy on the older boy showed severe axonal degeneration, numerous 'spheroids' in the gray matter, demyelinization, fibrosis, and loss of Purkinje fibers. Willi et al. (1997) reported the case of a 30-month-old girl with hypotonia, developmental delay, and tremor who, although consuming nominal quantities of meat, excreted large amounts of carnosine and anserine. A strict meat-free diet ameliorated, but did not eliminate, these abnormalities. Serum carnosinase activity was found to be extremely low.