What is a phakoma?

Phakomatoses are a set of genetic disorders that involve brain and skin anomalies, including hamartomas, usually in different organ systems, resulting from a dysregulation of the mammalian target of rapamycin (mTOR) pathway.

Many of these phakomatoses manifest with seizures, intellectual and developmental disabilities, ophthalmic abnormalities, skin conditions and other systemic dysfunctions, and most are highly variable and have variable progression and symptoms, which can mimic many diagnoses or conditions. They may not be evident at birth, and clinical findings usually appear with time, as the tumor suppressor gene affected in these conditions gradually decreases its function.

The first neurocutaneous diseases ever described (tuberous sclerosis and neurofibromatosis) were named, as "phakomatoses" by van der Hoeve in 1923, given their propensity to manifest with skin, and central nervous systems hamartomas. Currently, the term is extended to other non-dermatologic phakomatoses, some not clearly neurologically symptomatic.