Incontinentia pigmenti (Bloch-Sulzberger syndrome)

Incontinentia pigmenti (IP; Bloch-Sulzberger syndrome; OMIM #308300) is an X-linked dominant neurocutaneous disorder with presumed male lethality. It is usually diagnosed in female newborns based on skin features (erythematous, vesicular, or bullous eruption in linear streaks). The skin lesions evolve into a verrucous stage, followed by atrophy and scarring, leaving linear areas of hypopigmentation and hyperpigmented macules in bizarre patterns following Blaschko's lines. Systemic and neurologic complications include focal seizures and hemorrhagic cerebral infarction in infants, and retinal vasculopathy leading to blindness. Hypodontia, conical or pegged teeth, and linear areas of alopecia persist into adulthood. IP is caused by mutation of the IKBKG/NEMO gene on Xq28. Deletion of exons 4 to 10 (NEMOΔ4-10) accounts for about 80% of cases (familial and sporadic). NEMO mutation leads to loss of function of NF-κB, a critical protein that modulates cellular proliferation, apoptosis, and response to proinflammatory factors, leading to the characteristic features of IP. In female carriers, selective loss of cells expressing the mutant X-chromosome results in completely skewed X-inactivation in the majority of cases. Study of mouse models in which various components of the NF-κB pathway (including NEMO) have been knocked out has contributed significantly to our understanding of disease pathogenesis.