LOW CREATININE: THE DIAGNOSTIC CLUE FOR A TREATABLE NEUROLOGIC DISORDER

Abstract

A 22-month-old boy was referred for further evaluation of muscular hypotonia and mild psychomotor developmental delay. He was born as the second child to healthy, distantly related Caucasian parents following an uneventful pregnancy. The family history was not contributory. Routine neonatal screening for guanidinoacetate methyltransferase (GAMT) deficiency was done in this child, who was found to have a mildly elevated guanidinoacetate (GAA) level in the dry blood filter card on the fifth day of life. When recalled, his urinary GAA levels in a first sample were marginally elevated but were within normal limits in a second specimen. The likelihood of GAMT deficiency was considered to be low, although it is well known that false negative results may occur in neonatal screening programs. His neonatal period and early infancy were uneventful until a mild delay in his motor and speech development was noted at 6 months of age. Extensive workup including metabolic testing and MRI in a peripheral hospital revealed no abnormalities, although his serum …