HYDROXYPROLINEMIA - COMPARISON OF A PATIENT AND HER UNAFFECTED TWIN SISTER

Hydroxyproline is a major constituent of collagen. It accumulates as t he free imino acid in a rarely reported inborn error of metabolism kno wn as hydroxyprolinemia. This metabolic disorder was initially describ ed in association with mental retardation, but subsequent identificati on in clinically normal individuals has led to the supposition that it is benign. The possibility that hydroxyprolinemia might have an adver se effect on cognitive development without producing mental retardatio n has not been determined nor has its incidence been reported. We pros pectively studied a girl with untreated hydroxyprolinemia identified b y routine neonatal urine screening, the only infant found among 1 mill ion screened,and compared her with her unaffected dizygotic twin siste r. Plasma and urine hydroxyproline were increased approximately 10-fol d and 100-fold, respectively, in the affected twin. Both girls have ha d normal growth, with the affected twin taller than her sister. On neu ropsychologic testing, the affected twin was within normal limits, per forming slightly better than her sister on verbal and achievement test s but less well on visual perceptual testing. It appears that hydroxyp rolinemia has caused no physical or general cognitive deficits. The po ssibility of an effect on visual perceptual functioning, although unli kely, cannot be eliminated.