Incontinentia pigmenti, a Rare Genetic X-Linked Disorder of the Skin

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Skin disorder

What is most noticeable about this rare genetic disorder is the excessive discolouration of the skin which in children can develop as grey or brown swirly patches. It usually makes its first appearance between birth and the first six months as a blistering rash and is caused by excessive deposits of the normal skin pigment melanin. Generally the discolouration fades with time.

In later life there may also be dental problems and in some cases neurological disorders too, such as muscle spasms, reduced vision and seizures. There are many more symptoms such as retinal detachment, but their number and extent vary from person to person.

X-linked disorder

Incontinentia pigmenti is an X-linked dominantly inherited disorder that affects more females than males. In males it is usually (but not always) lethal.

It is inherited on the X chromosome and being dominant it only has to appear on one chromosome for the symptoms to show. It is not normally lethal in females because they have another X chromosome with a correct form of the NEMO gene. Males who do not have a working copy of NEMO tend not survive to birth.

Rare genetic disorder

The basis of this rare genetic disorder is a mutation in the NEMO/IKK-gamma gene. This gene makes a protein that regulates a protein complex (transcription factor nuclear factor KB; NF-KB) that prevents cells from self-destruction, when those cells are exposed to certain signals. In people with Incontinentia pigmenti the mutation results in a much smaller NEMO/IKK protein or a non-functional one. In 2000 the International Incontinentia Pigmenti Consortium concluded that the condition is caused by a genomic rearrangement of the NEMO gene.

Most of the mutations occur in the father’s testes during spermatogenesis and involve deletions of exons. Base pair substitutions have also been reported.

Incontinentia Pigmenti Treatment

Currently there aren’t any cures for this rare genetic disorder. The best that can be offered to patients is that their symptoms are managed. Regular dental check-ups for example are essential as is maintaining a good healthy balanced diet.

In terms of genetics, the best form of attack is knowing more about what we’re up against, and all the biochemical highways and byways that are involved. As the mutation is on a sex chromosome, germ line gene therapy is out of the question as it would not meet with ethical approval. But greater understanding will provide more targets for medicines.