Hyperglycinuria: a family report.

A 3-year-old girl with mental retardation and a cleft palate disclosed hyperglycinuria. Serum glycine concentration was within the normal limits and renal clearance of glycine was elevated. Oral loading test of glycine showed that the intestinal absorption of glycine seemed to be nonnal. With intravenous loading of glycine, maximum tubular reabsorption rate (Tm) for glycine could not be obtained. Intravenous infusion of L-proline indicated that the Tm for proline was about half the normal value and that the impaired glycine reabsorption was further depressed. The patient's mother also had a reduced Tm for proline although she did not exhibit distinct hyperglycinuria. It seems likely that the patient and her mother have a heterozygous trait for iminoglycinuria.