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(R)). 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 C-13-starch/breath (CO2)-C-13 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.

Congenital maltase-glucoamylase deficiency associated with lactase and sucrase deficiencies

Breath analysis has evolved into a technique that can support nicely the evaluation of patients with diarrhoea and/or weight loss and in whom nutrient malabsorption is a possibility. The lactose and sucrose breath hydrogen tests offer direct (and probably the most sensitive) documentation of the malabsorption of carbohydrate and are currently widely used for clinical analysis. The 14C-xylose breath test is the most sensitive and specific breath test for detecting bacterial overgrowth; it may be used in combination with the labelled bile acid breath test to make the latter a sensitive and specific test for ileal malabsorption of bile salts. The labelled fat breath test has promise in aiding the detection and/or cause of fat malabsorption, but requires modification for optimum sensitivity and utility in quantifying the level of fat absorption.

The use of breath tests in the study of malabsorption.

The frequency of negative hydrogen breath tests due to colonic bacterial flora which are unable to produce hydrogen was determined after oral lactulose challenge in 98 healthy Dutch schoolchildren. There was a negative result in 9.2%. The probability of a false normal lactose breath test (1:77) was calculated from these results together with those from a separate group of children with lactose malabsorption (also determined by hydrogen breath test). A study of siblings and mothers of subjects with a negative breath test did not show familial clustering of this condition. Faecal incubation tests with various sugars showed an increase in breath hydrogen greater than 100 parts per million in those with a positive breath test while subjects with a negative breath test also had a negative faecal incubation test. The frequency of a false negative hydrogen breath test was higher than previously reported, but this does not affect the superiority of this method of testing over the conventional blood glucose determination.

https://adc.bmj.com/content/archdischild/60/4/333.full.pdf

Hydrogen breath test in schoolchildren.

Thirty-eight infants and young children with gastroenteritis were investigated for lactose malabsorption. Each of them was given an oral lactose load of either 0.5 g/kg or 2 g/kg after which breath hydrogen excretion was measured, and each was observed to see if he had clinical symptoms of lactose intolerance. Only one patient, given 2 g/kg lactose, had clinical intolerance. His breath hydrogen excretion however was negative. Three of 18 patients given 0.5 g/kg lactose had positive breath hydrogen tests. None of these was symptomatic. Lactose intolerance in gastroenteritis was rare in our study, and the hydrogen breath test was not an appropriate technique for detecting it.

https://adc.bmj.com/content/archdischild/56/5/364.full.pdf

Lactose malabsorption during gastroenteritis, assessed by the hydrogen breath test.

Sucrose breath hydrogen tests were performed on 7 children with proved sucrase isomaltase deficiency. All children had raised breath hydrogen excretion. The amount of hydrogen produced and symptoms experienced increased with increasing sucrose loads. The sucrose breath hydrogen test appears to be a reliable indicator of sucrose malabsorption in sucrase isomaltase deficiency.

https://adc.bmj.com/content/archdischild/58/8/595.full.pdf

Breath hydrogen test and sucrase isomaltase deficiency.

Five patients with sucrase-isomaltase deficiency, and one patient with primary glucose-galactose malabsorption had no increases in breath hydrogen excretion after oral sucrose or glucose. Anaerobic incubation with sugars of stool suspensions from 5 patients with primary sugar malabsorption produced by trace of hydrogen (17 microliter) in only one, while those from 13 or 14 controls produced a mean hydrogen volume of 640 microliter under similar conditions. Altered bacterial metabolism is a probable explanation. Breath hydrogen excretion did increase appreciably in 2 of these patients after oral lactulose showing that hydrogen excretion may vary according to the substrate. Therefore, observation of breath hydrogen excretion after lactulose is not recommended as a means of predicting false-negative breath tests with other sugars. The hydrogen breath test is not a reliable mean of diagnosing primary sugar malabsorption in children.

https://adc.bmj.com/content/archdischild/56/5/368.full.pdf

Failure of the hydrogen breath test to detect pulmonary sugar malabsorption.

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Failure of the hydrogen breath test to detect pulmonary sugar malabsorption.