Piebaldism

Definition

Piebaldism is a rare autosomal dominant pigmentary disorder with a congenital white forelock (poliosis) and circumscribed, stable depigmented patches of skin (leukoderma) that are present at birth.

Aetiopathogenesis

Piebaldism is a neurocristopathy: loss-of-function mutations in the KIT proto-oncogene on chromosome 4 disturb the embryonic migration of melanoblasts from the neural crest, so that melanocytes are absent from the affected areas. Some patients without a KIT mutation have deletions of the SNAI2 (SLUG) gene on chromosome 8. Severity depends on the mutation but is also influenced by modifier genes such as MC1R. Each child of an affected parent has a 50% chance of inheriting the condition.

Clinical features

• White forelock in 80–90% of patients with leukoderma of the central forehead; the eyebrows and eyelashes may also be affected.
• Further white patches on the face (especially the chin), ventral trunk and limbs; hands and feet are usually spared.
• Often a narrow hyperpigmented border; within the white areas islands of normally or hyperpigmented skin.
• Café-au-lait macules and flexural freckling may develop.
• Mild forms show only small white patches. Complications: sunburn and skin cancer in the depigmented areas, psychosocial burden.

Diagnosis

• Clinical diagnosis suspected at or soon after birth.
• Biopsy of leukoderma: complete absence of melanocytes and melanin pigment.
• Molecular genetic testing of blood can confirm the diagnosis.
• Distinction from, among others, vitiligo (acquired, different distribution) and Waardenburg syndrome (additionally deafness, increased distance between the eyes).

Differential diagnoses

• Vitiligo
• Oculocutaneous albinism
• Naevus depigmentosus (achromic naevus)
• Hypomelanosis of Ito (incontinentia pigmenti achromians)
• Incontinentia pigmenti

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References (selection)

1. DermNet: Piebaldism
2. PubMed: Piebaldism (J Dermatol) (PMID 22670867)
3. PubMed: Piebaldism in children (PMID 26919497)
4. PubMed: Deletion of the SLUG (SNAI2) gene results in human piebaldism (PMID 12955764)

Cross-references