Abstract
A diagnosis of Type I hyperprolinaemia was made in a 7-month-old infant who presented with hypocalcaemic convulsions and malabsorption. The plasma levels of proline were grossly raised and the urinary excretion of proline, hydroxyproline, and glycine was increased; neurological development was delayed and there were associated abnormalities of the electroencephalogram, renal tract, and bones. Restriction of dietary proline at the age of 9 months resulted in a prompt fall of plasma levels of proline to normal, and a low proline diet was continued until the age of 27 months when persistence of the biochemical defect was shown. During the period of dietary treatment, growth was satisfactory, mental development improved, and the electroencephalogram, and the renal, skeletal, and intestinal abnormalities disappeared. Proline should be regarded as a `semi-essential' amino acid in the growing infant.