Epidermolytic ichthyosis in a child and systematized epidermolytic nevi in the mosaic parent associated with a KRT1 variant.

Epidermolytic ichthyosis and epidermolytic nevi share the same histopathological features of epidermolytic hyperkeratosis, characterized by distinctive vacuolar degeneration and hypergranulosis of the superficial epidermis. Both are caused by pathogenic variants in either of two keratin genes KRT1or KRT10, with epidermolytic ichthyosis presenting as a generalized phenotype and epidermolytic nevi presenting as a mosaic phenotype. We report a boy who presented as epidermolytic ichthyosis, with diffuse erythema, superficial erosions and flaccid blisters at birth progressing to generalized ichthyosis. He was found to have inherited a novel KRT1 variant from his mother who presented with extensive epidermolytic nevi or mosaic form of epidermolytic ichthyosis, with extensive, linear and Blaschkoid verrucous, hyperkeratotic plaques over the trunk and limbs. This case highlights the importance of recognising post-zygotic mosaicism which might be transmitted to a child, and the different presentations for germline and mosaic carriers.