Hypersarcosinemia: New Observations

Abstract

Sarcosinuria was found in a 10-year-old French-Canadian boy with normal IQ, small stature (< 3rd percentile) and bilateral contractures of lower limb muscles. Coexistent hypersarcosinemia (0.18–0.34 μM; normal <0.02 μM) was unmodified by large supplements of folic acid, the coenzyme for the presumably abnormal apoenzyme, sarcosine dehydrogenase. It is appropriate to screen urine for this trait, since sarcosine is cleared rapidly by kidney (8–35 ml/min/1.73 m2). The Tm sarcosine is about 160 μmoles/min/1.73 m2 in the ‘blocked catabolic mutant’. Sarcosine appears to interact weakly with a system shared by imino-acids and glycine. Sarcosine loading (100 mg/kg p.o.) produced 3 different responses in subjects. Normal: rapid disappearance of sarcosine from plasma (t ½ ˜ 30 min) with a fall in plasma glycine. Proband: greatly delayed disappearance of plasma sarcosine (t ½ ˜ 153 min) with no change in plasma glycine. Parents of proband: initial plasma sarcosine concentration normal but delayed disappearance of plasma sarcosine (t ½ ˜ 68 min) with a rising plasma glycine level. These findings suggst the trait is autosomal recessive in this pedigree. We were unable to detect sarcosine dehydrogenase activity in normal skin fibroblasts sub-cultured for 14 regenerations: consequently lack of activity in the proband's fibroblasts is of no significance. (Research supported by grants from Qubec MRC and MRC, Canada.)