Purpose: To report the clinical and molecular genetic findings in two brothers with retinitis pigmentosa (RP) and mevalonate kinase deficiency (MKD). Methods: The brothers were examined clinically and with fundus autofluorescence, near-infrared auto fluorescence, and Spectral domain optical coherence tomography. Targeted resequencing was done with a custom designed gene panel containing 78 genes associated with RP. Mutations were confirmed by direct Sanger sequencing. Results: Both brothers, aged 46 and 47 years, were found to carry compound heterozygous mutations in the MVK gene (c.59A>C, c.1000G>A) encoding mevalonate kinase. They presented with severe ataxia, pseudophakia due to early onset cataract, and progressed retinitis pigmentosa. In one brother with cystoid macular edema, treatment with dorzolamide was beneficial. Serum IgD levels were markedly increased in both brothers and mevalonic acid blood and urine levels were markedly increased in, the one brother who could be examined. The disease severity differed between the brothers one had more severe ataxia and less severe visual deficiency compared to the other. Conclusion: MKD can be associated with RP and early onset cataract. Most MKD patients developing RP carry the (p.Ala334Thr) mutation. Macular edema can be treated using local dorzolamide
