Random Dermatology MCQ - Pseudoxanthoma Elasticum (PXE)

A 25-year-old woman presents with yellowish, papular plaques on the side of her neck and flexural areas, giving the skin a "plucked chicken" appearance. She also reports gradual visual impairment. Ophthalmologic examination reveals angioid streaks. Which of the following is the most likely underlying genetic defect?

A) Mutation in the ABCC6 gene
B) Deficiency of the ATP7A copper transporter
C) Mutation in the FBN1 gene
D) Defect in the ELN gene
E) Mutation in the KRT5 gene

Correct Answer: A) Mutation in the ABCC6 gene

Explanation

This is a classic presentation of Pseudoxanthoma Elasticum (PXE), a disorder of ectopic mineralization.

• Clinical Triad:

  1. Skin: Yellowish, cobblestoned papules and plaques in flexural areas (neck, axillae, groin) – the "plucked chicken" or "Moroccan leather" sign.

  2. Eyes: Angioid streaks (fissures in Bruch's membrane), which can lead to hemorrhage and vision loss.

  3. Cardiovascular: Premature atherosclerosis, hypertension, and gastrointestinal bleeding.

• Pathogenesis: Caused by mutations in the ABCC6 gene on chromosome 16p13.1. This gene encodes a transmembrane transporter protein primarily expressed in the liver and kidneys. Its dysfunction leads to reduced circulating factors that inhibit mineralization, resulting in calcium deposition in elastic tissues of the skin, eyes, and blood vessels.

• Why Not the Others?

  • (B) ATP7A: Causes Menkes disease (kinky hair, neurologic deficits).

  • (C) FBN1: Causes Marfan syndrome (aortic dissection, arachnodactyly).

  • (D) ELN: Associated with supravalvular aortic stenosis (Williams syndrome) or cutis laxa.

  • (E) KRT5: Causes Epidermolysis Bullosa Simplex (blistering after trauma).

Management: There is no cure. Treatment is multidisciplinary, focusing on surveillance and complications:

• Dermatology: Reassurance, cosmetic management.

• Ophthalmology: Regular eye exams to monitor for choroidal neovascularization.

• Cardiology: Monitoring for cardiovascular disease and hypertension.

• Gastroenterology: Investigating any GI bleeding.