Neurocutaneous disorders are a heterogeneous group of conditions (mainly) affecting the skin [with pigmentary/vascular abnormalities and/or cutaneous tumours] and the central and peripheral nervous system [with
congenital abnormalities and/or tumours]. In a number of such disorders, the
skin abnormalities can assume a mosaic patterning (usually arranged in archetypical patterns). Alternating segments of affected and unaffected skin or segmentally arranged patterns of abnormal skin often mirror similar phenomena occurring in extra-cutaneous organs/tissues [eg, eye, bone, heart/vessels, lung, kidney and gut]. In some
neurocutaneous syndromes the abnormal mosaic patterning involve mainly the skin and the nervous system configuring a (true) mosaic
neurocutaneous disorder; or an ordinary trait of a
neurocutaneous disorder is sometimes superimposed by a pronounced linear or otherwise segmental involvement; or, lastly, a
neurocutaneous disorder can occur solely in a mosaic pattern. Recently, the molecular genetic and cellular bases of an increasing number of
neurocutaneous disorders have been unravelled, shedding light on the interplays between common intra- and extra-neuronal signalling pathways encompassing receptor-
protein and
protein-to-
protein cascades (eg, RAS, MAPK, mTOR, PI3K/AKT and GNAQ pathways), which are often responsible of the mosaic distribution of cutaneous and extra-cutaneous features. In this article we will focus on the well known, and less defined mosaic neurocutaneous phenotypes and their related molecular/genetic bases, including the mosaic
neurofibromatoses and their related forms (ie, spinal
neurofibromatosis and
schwannomatosis);
Legius syndrome; segmental arrangements in
tuberous sclerosis; Sturge-Weber and
Klippel-Trenaunay syndromes;
microcephaly/
megalencephaly-capillary malformation;
blue rubber bleb nevus syndrome;
Wyburn-Mason syndrome; mixed vascular
nevus syndrome; PHACE syndrome;
Incontinentia pigmenti; pigmentary mosaicism of the Ito type;
neurocutaneous melanosis; cutis tricolor; speckled lentiginous syndrome;
epidermal nevus syndromes; Becker's
nevus syndrome;
phacomatosis pigmentovascularis and pigmentokeratotica;
Proteus syndrome; and
encephalocraniocutaneous lipomatosis.