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Condition report · Gastrointestinal

Congenital Sucrase-Isomaltase Deficiency

Inherited deficiencies of the gut enzymes that digest dietary sugars, causing diarrhoea, bloating and abdominal pain after eating sucrose, starch or lactose. Both are managed mainly through diet.

A condition report looks for rare variants known to cause the conditions it covers.

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The 2 conditions we analyse

Congenital sucrase-isomaltase deficiency (CSID)

Autosomal recessive · Rare in most populations, but estimated at about 3 to 10% of Greenlandic and Canadian Inuit.

A deficiency of the sucrase-isomaltase enzyme, caused by SI variants, that impairs digestion of sucrose and some starches.

What a diagnosis changes

Dietary restriction of sucrose and starch, with sacrosidase enzyme replacement, controls symptoms, and a diagnosis can explain long-standing IBS-like symptoms.

Genes analysed

Also known as

congenital sucrose intolerance; congenital sucrose-isomaltase malabsorption; CSID; disaccharide intolerance; disaccharide intolerance, 1; genetic sucrase-isomaltose malabsorption; sucrase-isomaltase deficiency; sucrase-isomaltase deficiency, congenital; sucrose isomaltose enzyme deficiency

Includes 6 related subtypes ↓
  • congenital sucrase-isomaltase deficiency with minimal starch tolerance
  • congenital sucrase-isomaltase deficiency with starch and lactose intolerance
  • congenital sucrase-isomaltase deficiency with starch intolerance
  • congenital sucrase-isomaltase deficiency without starch intolerance
  • congenital sucrase-isomaltase deficiency without sucrose intolerance
  • global disaccharide intolerance
MONDO:0009114OMIM 222900Orphanet 35122MedGen 220924

Congenital lactase deficiency

Autosomal recessive

A severe deficiency of the lactase enzyme from birth, caused by LCT variants, that causes watery diarrhoea once milk feeding begins.

What a diagnosis changes

A lactose-free diet resolves symptoms and prevents dehydration and poor growth in infancy.

Genes analysed

MONDO:0009115OMIM 223000Orphanet 53690MedGen 120617

Limitations

  • Some common SI missense variants reduce enzyme activity only partly and need careful interpretation; carrying one SI variant does not mean someone has CSID.
  • This report does not cover the common adult lactose intolerance trait (lactase non-persistence), which is determined by non-coding variants near LCT and is not a disease.

Other gastrointestinal conditions

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