Long-Read Sequencing is Required for Precision Diagnosis of Incontinentia Pigmenti.

Incontinentia pigmenti (IP) is caused by loss-of-function variants in , with molecular genetic diagnosis complicated by a pseudogene. We describe seven individuals from three families with IP but negative clinical testing in whom long-read sequencing identified causal variants. Concurrent methylation analysis explained disease severity in one individual who died from neurologic complications, identified a mosaic variant in an individual with an atypical presentation, and confirmed skewed X-chromosome inactivation in an XXY individual.