Slowly progressive retinitis pigmentosa caused by two novel mutations in the MAK gene

The growing number of clinical trials currently underway for inherited retinal diseases has highlighted the importance of achieving a molecular diagnosis for all new cases presenting to hospital eye services. The male germ cell-associated kinase (MAK) gene encodes a cilium-associated protein selectively expressed in the retina and testis, and has recently been implicated in autosomal recessive retinitis pigmentosa (RP). Whole exome sequencing has previously identified a homozygous Alu insertion in probands with recessive RP and nonsense and missense mutations have also been reported.

Here we describe two novel mutations in different alleles of the MAK gene in a 75-year-old British female, who had a clinical diagnosis of RP () with onset in the fourth decade and no relevant family history. The mutations were established through next generation sequencing of a panel of 111 genes associated with RP and RP-like phenotypes.

Two novel null mutations were identified within the MAK gene. The first c.1195_1196delAC p.(Thr399fs), was a two base-pair deletion creating a frame-shift in exon 9 predicted to result in nonsense-mediated decay. The second, c.279-2A>G, involved the splice acceptor consensus site upstream of exon 4, predicted to lead to aberrant splicing.

The natural history of this individual's RP is consistent with previously described MAK mutations, being significantly milder than that associated with other photoreceptor ciliopathies. We suggest inclusion of MAK as part of wider genetic testing in all individuals presenting with RP.