U01.01.036 Menkes disease

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Learning Objectives

  • Identify the genetic inheritance and the specific protein defect in Menkes disease.
  • Explain how copper deficiency leads to defective collagen cross-linking.
  • Distinguish Menkes disease (ATP7A) from Wilson disease (ATP7B).
  • Recognize the classic clinical triad: kinky hair, hypotonia, and growth delay.

1. Pathophysiology: The ATP7A Defect

Menkes disease is an X-linked recessive connective tissue disorder. It is fundamentally a problem of copper distribution.

  • The Defect: Mutations in the ATP7A protein lead to impaired intestinal copper absorption and transport.
  • “A is for Absent”: Think of ATP7A as causing Absent copper in the body’s tissues (vs. ATP7B in Wilson disease, where copper Builds up in the liver and brain).

2. Mechanism: Collagen Cross-linking

Copper is a mandatory cofactor for several enzymes. When copper is “absent” or low, these enzymes cannot function.

  • Lysyl Oxidase: This copper-dependent enzyme is responsible for the cross-linking of tropocollagen into stable collagen fibers.
  • The Result: Decreased (\downarrow) lysyl oxidase activity → Defective collagen cross-linking → Structurally weak connective tissue.

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3. Clinical Presentation

Symptoms typically appear in early infancy due to the widespread need for copper in the CNS and connective tissues.

  • “Kinky” Hair: Also known as pili torti; hair is brittle, sparse, and has a steel-wool texture.
  • Neurological: Severe hypotonia (floppy baby syndrome), seizures, and significant developmental delay.
  • Vascular: Increased (\uparrow) risk of cerebral aneurysms due to weak arterial walls.
  • Growth: Failure to thrive and growth retardation.

4. Menkes vs. Wilson Disease

Feature Menkes Disease Wilson Disease
Gene ATP7A ATP7B
Copper Status Systemic Deficiency (Absent) Systemic Overload (Buildup)
Inheritance X-linked Recessive Autosomal Recessive
Key Finding Kinky hair, weak collagen. Kayser-Fleischer Rings, Cirrhosis.

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