U01.01.101 Lactase deficiency

Lactase deficiency occurs when there is an insufficient amount of the lactase enzyme, leading to an inability to properly digest lactose found in milk and dairy products. Lactase is normally active on the intestinal brush border, breaking down lactose into glucose and galactose.

Types of Lactase Deficiency:

Primary Lactase Deficiency
- Cause: Age-dependent decline in lactase production after childhood.
- Prevalence: More common in individuals of Asian, African, or Native American descent.
- Mechanism: Absence of the lactase-persistent allele.
Secondary Lactase Deficiency
- Cause: Loss of the intestinal brush border due to factors like gastroenteritis (e.g., rotavirus) or autoimmune diseases.
- Associated Conditions: Rotavirus infection, celiac disease, Crohn’s disease, etc.
Congenital Lactase Deficiency
- Cause: Rare genetic defect leading to complete absence of lactase.
- Mechanism: Inherited mutation affecting the lactase gene.

Diagnostic Findings:

Test	Expected Result
Stool pH	Decreased (due to fermentation of undigested lactose)
Hydrogen Breath Test	Increased hydrogen content (produced by bacterial fermentation of undigested lactose)
Intestinal Biopsy	Normal mucosa in hereditary lactose intolerance

Clinical Presentation:

Symptoms:
- Bloating
- Cramps
- Flatulence
- Osmotic diarrhea (loose stools with high water content)

Management:

Dietary Adjustments:
- Avoid dairy products.
- Use lactase supplements (e.g., lactase pills) or lactose-free milk.

Key Points to Remember for the USMLE Step 1:

Lactase deficiency is a common cause of gastrointestinal distress after milk consumption.
Primary lactase deficiency is more prevalent in certain ethnic groups (Asian, African, Native American).
Secondary lactase deficiency is due to damage to the intestinal mucosa, often from infections like rotavirus.
The breath hydrogen test is an essential diagnostic tool.
Treatment typically involves lactose avoidance, lactase supplements, or lactose-free dairy alternatives.

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