Congenital Ichthyosis 4A and 4B (ABCA12)
Pathogenic variants in the gene ABCA12 cause two autosomal recessive retinal disorders: congenital ichthyosis 4A (also known as lamellar ichthyosis) and congenital ichthyosis 4B (also known as harlequin ichthyosis).
- Individuals with congenital ichthyosis 4A are usually born with a collodion membrane (a shiny, tight layer of skin over the body which is shed within the first two weeks of life) and will typically develop skin symptoms in infancy. These symptoms usually include brown scales over the entire body, inversion of the eyelids and lips, thickening of skin on the palms and soles of the feet, and hair loss with some scarring. Some individuals also have reduced mobility due to skin stiffness. In severe cases, individuals may die from sepsis or electrolyte imbalance in infancy. Those who survive infancy typically have a normal life expectancy.
- Individuals with congenital ichthyosis 4B are usually born prematurely and have very hard, thick, armor-like plates of skin covering most of their bodies. The plates of skin are separated by deep cracks that are susceptible to infections. Individuals also have severe restriction of movement of the chest that can lead to respiratory distress and feeding difficulties. Without medical intervention, this disorder is typically fatal in infancy. Those who survive infancy typically develop symptoms similar to congenital ichthyosis 4A. No clear genotype-phenotype correlation has been established.
For information about carrier frequency and residual risk, please see the residual risk table.