Figure 5.

Drawing illustrating the unifying (allelic) dydymotic theory as a pathogenic explanation for the cutis tricolor phenotypes: (A) a post zygotic somatic mutation leading to heterozygosity for the underlying yet undiscovered gene responsible for the skin anomaly at an early developmental stage would give rise to a complex malformation mosaic pattern (e.g., syndromic cutis tricolor) whilst, at a later embryonic stage would give rise to pure cutaneous traits (i.e., manifestations confined to the skin only) or to the distinct type of cutis tricolor parvimaculata. These heterozygous cutaneous cell populations (grey and white cells in the figure) can generate in the skin (A) either archetypical or less-well defined mosaic patterns. Similar phenomena occur in the bone (skeletal abnormalities) (B), in the lenses (C) [note the different populations of cortical-subcortical lens cells migrating in parallel streaks [as found at histopathology in the cataracts of children with cutis tricolor, see (12)], and in the nervous system (D), generating layers disarraying in the subcortical white matter leading to delayed myelination or to clones of disordered neuronal cells.