U01.01.107 Disorders of galactose metabolism

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Learning Objectives

  • Differentiate between the mild clinical course of Galactokinase Deficiency and the life-threatening Classic Galactosemia.
  • Explain the role of Galactitol in the development of infantile cataracts.
  • Recognize the classic neonatal presentation of GALT deficiency, including the risk of E. coli sepsis.
  • Identify the necessary dietary exclusions required to treat these autosomal recessive disorders.

1. Comparison of Galactose Disorders

Galactose is primarily derived from lactose (found in breast milk and formula). When the enzymes responsible for its conversion to glucose are deficient, toxic metabolites accumulate.

Feature Galactokinase Deficiency Classic Galactosemia
Enzyme Deficiency Galactokinase Galactose-1-phosphate uridyltransferase (GALT)
Pathophysiology Galactosemia/galactosuria; Galactitol accumulates in the lens. Accumulation of toxic Galactose-1-P and Galactitol.
Primary Finding Infantile cataracts; failure to track objects or social smile. Failure to thrive, jaundice, hepatomegaly, cataracts, ID.
Systemic Impact Mild / Benign. Severe; predisposes to E. coli sepsis.

2. The Role of Galactitol

When the main metabolic pathways for galactose are blocked, the enzyme Aldose Reductase converts excess galactose into Galactitol.

  • Osmotic Damage: Galactitol is osmotically active and draws water into the lens of the eye.
  • Cataracts: This process leads to the permanent opacification of the lens, presenting as infantile cataracts.

High-Yield Point:

Symptoms of Classic Galactosemia start as soon as the infant begins feeding (breast milk or formula) because Lactose is a disaccharide of Glucose + Galactose.

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3. Treatment and Dietary Management

Management for both conditions requires the immediate and strict exclusion of galactose sources from the diet.

  • Exclude Galactose: Found in many dairy products and some fruits/vegetables.
  • Exclude Lactose: Since lactose is broken down into galactose, it must be completely removed (switch to soy-based formula).

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Memory Hook: GalactoKinase deficiency is Kinder (mostly just cataracts).

Classic Galactosemia is Crushing (Liver failure, Sepsis, and ID).

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