Background: Multiple enzyme deficiencies have been reported in some cases of congenital glucoamylase, sucrase, or lactase deficiency. Here we describe such a case and the investigations that we have made to determine the cause of this deficiency.
Methods and Results: A 2.5 month-old infant, admitted with congenital lactase deficiency, failed to gain weight on a glucose oligomer formula (Nutramigen®). Jejunal mucosal biopsy at 4 and 12 months revealed normal histology with decreased maltase-glucoamylase, sucrase-isomaltase, and lactase-phlorizin hydrolase activities. Testing with a 13C-starch/breath 13CO2 loading test confirmed proximal starch malabsorption. Sequencing of maltase-glucoamylase cDNA revealed homozygosity for a nucleotide change (C1673T) in the infant, which causes an amino acid substitution (S542L) 12 amino acids after the N-terminal catalytic aspartic acid. The introduction of this mutation into “wildtype” N-terminus maltase-glucoamylase cDNA was not associated with obvious loss of maltase-glucoamylase enzyme activities when expressed in COS 1 cells and this amino-acid change was subsequently found in other people. Sequencing of the promoter region revealed no nucleotide changes. Maltase-glucoamylase, lactase, and sucrase-isomaltase were each normally synthesized and processed in organ culture.
Conclusions: The lack of evidence for a causal nucleotide change in the maltase-glucoamylase gene in this patient, and the concomitant low levels of lactase and sucrase activity, suggest that the depletion of mucosal maltase-glucoamylase activity and starch digestion was caused by shared, pleiotropic regulatory factors.
*USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas, U.S.A.; †Galton Laboratory, Department of Biology University College London, London, U.K.; and ‡Institute of Biochemistry and Molecular Biology, University of Bern, Switzerland
Received January 31, 2002; accepted June 24, 2002.
Address correspondence to Buford L. Nichols, Department of Pediatrics Baylor College of Medicine, 1100 Bates Street, Houston, TX 77030-2600, U.S.A. (e-mail: email@example.com).