Retinitis Pigmentosa - Diagnosis

Diagnosis

The diagnosis of retinitis pigmentosa relies upon documentation of progressive loss in photoreceptor cell function by electroretinography (ERG) and visual field testing.

The mode of inheritance of RP is determined by family history. At least 35 different genes or loci are known to cause "nonsyndromic RP" (RP that is not the result of another disease or part of a wider syndrome).

DNA testing is available on a clinical basis for:

• RLBP1 (autosomal recessive, Bothnia type RP)
• RP1 (autosomal dominant, RP1)
• RHO (autosomal dominant, RP4)
• RDS (autosomal dominant, RP7)
• PRPF8 (autosomal dominant, RP13)
• PRPF3 (autosomal dominant, RP18)
• CRB1 (autosomal recessive, RP12)
• ABCA4 (autosomal recessive, RP19)
• RPE65 (autosomal recessive, RP20)

For all other genes (e.g. DHDDS), molecular genetic testing is available on a research basis only.

RP can be inherited in an autosomal dominant, autosomal recessive, or X-linked manner. X-linked RP can be either recessive, affecting primarily only males, or dominant, affecting both males and females, although males are usually more mildly affected. Some digenic (controlled by two genes) and mitochondrial forms have also been described.

Genetic counseling depends on an accurate diagnosis, determination of the mode of inheritance in each family, and results of molecular genetic testing.