Mutation analysis identifies GUCY2D as the major gene responsible for autosomal dominant progressive cone degeneration

Abstract

Purpose: Heterozygous mutations in the GUCY2D gene, which encodes the membrane-bound retinal guanylyl cyclase-1 protein (RetGC-1), have been shown to cause autosomal dominant inherited cone degeneration and cone-rod degeneration (adCD, adCRD). The present study was a comprehensive screening of the GUCY2D gene in 27 adCD and adCRD unrelated families of these rare disorders.

Methods: Mutation analysis was performed by direct sequencing as well as PCR and subsequent restriction length polymorphism analysis (PCR/RFLP). Haplotype analysis was performed in selected patients by using microsatellite markers.

Results: GUCY2D gene mutations were identified in 11 (40%) of 27 patients, and all mutations clustered to codon 838, including two known and one novel missense mutation: p.R838C, p.R838H, and p.R838G. Haplotype analysis showed that among the studied patients only two of the six analyzed p.R838C mutation carriers shared a common haplotype and that none of the p.R838H mutation carriers did.

Conclusions: GUCY2D is a major gene responsible for progressive autosomal dominant cone degeneration. All identified mutations localize to codon 838. Haplotype analysis indicates that in most cases these mutations arise independently. Thus, codon 838 is likely to be a mutation hotspot in the GUCY2D gene.

Figure 1

Pedigrees of adCD and adCRD families segregating GUCY2D gene mutations. Arrows: index patients initially screened for GUCY2D mutations. Genotypes of family members whose DNA samples were available are listed below the respective subject. Horizontal bars above symbols: patients who underwent clinical examination. Pedigrees are arranged from left to right and top to bottom in the same order as patients are listed in Table 3. The pedigree number is given above and to the left of each pedigree.

Figure 2

Patients with GUCY2D gene mutations typically had only mild fundus alterations. Apart from slightly narrowed retinal vessels, the fundus of patient ZD138/9058 showed no alterations of the central and peripheral retina (A). Patient ZD181/5003 had a slightly pale optic disc, a somewhat mottled macular RPE, and thinning of the RPE nasally to the macula, but no alterations of the peripheral retina (B, peripheral retina not shown). Within families, fundus alterations were more pronounced in the older generations. For example, 6-year-old patient ZD249/15965 had a subtle central RPE atrophy (E), but his grand uncle at 61 years of age had marked macular RPE atrophy (G). His son at the age of 31 showed less severe atrophy of the macular RPE (F). All three, however, had a normal peripheral retina. Whereas most patients had only changes in the macula, one patient (RCD62/5127) had alterations both in the macula and periphery (C, D) with marked narrowing of the retinal vessels, widespread RPE atrophy and bone spicules in the periphery, which were in part more pronounced around the vessels.