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When pathogenic variants in two different genes are required for a particular condition or trait to present (one variant alone is not sufficient to produce the phenotype).

Use in clinical context

In digenic inheritance, the proteins encoded by the genes involved typically have similar functions or are involved in the same cellular pathway. There is little or no effect on phenotype when only one of the genes encoding these proteins has a pathogenic variant, because the unaffected protein can compensate. However, when both genes have a pathogenic variant both proteins are affected, compensation is not possible and there is impairment of function sufficient to produce the phenotype.

There are several conditions in which digenic inheritance has been identified, most notably retinitis pigmentosa. Retinitis pigmentosa is an inherited eye condition of which there are many sub-types, causing progressive retinal degeneration. It is typically inherited in an autosomal dominant, autosomal recessive or X-linked recessive pattern. Rarely, when variants are present in both the ROM1 and PRPH2 genes, retinitis pigmentosa can arise in a digenic pattern.

Last updated on 15th August, 2023