Progressive cone-rod dystrophy and high myopia in a Finnish family

A novel large in-frame deletion within the CACNA1F gene associates with a cone-rod dystrophy 3-like phenotype

Cone-rod dystrophies (CORDs) represent a heterogeneous group of monogenic diseases leading to early impairment of vision. The majority of CORD entities show autosomal modes of inheritance and X-linked traits are comparably rare. So far, three X-chromosomal entities were reported (CORDX1, -X2 and -X3). In this study, we analysed a large family of German origin with solely affected males over three generations showing a CORDX-like phenotype. Due to the heterogeneity of cone-rod dystrophies, we performed a combined linkage and X-exome sequencing approach and identified a novel large intragenic in-frame deletion encompassing exons 18 to 26 within the CACNA1F gene. CACNA1F is described causative for CORDX3 in a single family originating from Finland and alterations in this gene have not yet been reported in other CORDX pedigrees. Our data independently confirm CACNA1F as the causative gene for CORDX3-like phenotypes and detailed clinical characterization of the family expands the knowledge about the phenotypic spectrum of deleterious CACNA1F alterations.

Genetic isolates in ophthalmic diseases

In recent years, noteworthy gains have been made in unravelling the genetic contribution to some complex ocular diseases, principally age-related macular degeneration. Yet, a relatively poor understanding of the genetic aetiology for many other heritable blinding diseases, such as glaucoma, keratoconus and myopia, remains. Genetic isolates, populations with varying degrees of geographical or cultural seclusion, provide an effective means for investigating the molecular mechanisms involved in human diseases. This is particularly true for rare diseases in which founded alleles can be rapidly driven to a high frequency due to restriction of gene flow in the population. Recent success in complex gene mapping has resulted from the widened linkage disequilibrium (LD) in the genome of genetically isolated populations. An improved understanding of the predisposing genetic risk factors allows for enhanced screening modalities and paves the foundations for the translation of genomic technology into the clinic. This review focuses on the role population isolates have had in the investigation of genes underlying complex eye diseases and discusses their likely usefulness given the expansion of large-scale case-control association studies.

Clinical features and a follow-up study in a family with X-linked progressive cone-rod dystrophy

PURPOSE

To study a large family with X-linked progressive cone-rod dystrophy.

METHODS

There were 128 members in the family. Of these, 45 had an ophthalmological examination and 3 gave their permission to use the results of their recent ophthalmological examination. In addition to the usual eye examination, visual fields, colour vision, dark adaptation and electroretinogram (ERG) were examined.

RESULTS

Ten affected men aged 6 to 81 years were found in the family. The visual acuities varied from counting fingers (cf) 10 cm to 0.5 in the right eye (RE) and from cf 30 cm to 0.4 in the left eye (LE). The refraction was myopic in all affected members, varying from -1.5 to -24.0 D (RE) and from -2.0 to -20.25 D (LE). In visual functions, central scotomas and concentric constriction in the visual fields, red or red-green defects in colour vision, abnormal cone and rod dark adaptation and affected cone response in ERG were found. The 6 obligate carriers were aged 17 to 77 years. Their visual acuities varied from 0.05 (strabismic amblyopia) to 1.25(RE) and from 0.7 to 1.25 (LE), and refraction from +/-0 to +6.0 D (RE) and from -0.5 to +5.0 D (LE). Their visual fields and colour vision were normal. The non-affected men were aged 13 to 55 years, their visual acuity was normal in both eyes, and refraction varied from -5.0 to +1.5 D (RE) and from -5.5 to +1.75 (LE). The result of the eye examination was normal except in colour vision: two men were congenitally deuteranomalous. The women who were not obligate carriers were aged 10 to 77 years, their visual acuity was from 0.3 to 1.6 in both eyes, and refraction from -5.5 to +4.75 (RE) and from -5.25 to +4.0 (LE). Two women had one amblyopic eye. Otherwise the eye examination was normal.

CONCLUSIONS

The clinical diagnosis of X-linked cone dystrophy 1 (COD1) is based on progressive loss of visual acuity, moderate or high myopia, red colour vision defect and affected cone response or cone and rod response in ERG. The future identification of the COD1 gene will confirm the diagnosis of the disease and help in genetic counseling of the family.

Aplasia cutis congenita, high myopia, and cone-rod dysfunction in two sibs: a new autosomal recessive disorder

We report on a brother and a sister with congenital nystagmus, cone-rod dysfunction, high myopia, and aplasia cutis congenita on the midline of the scalp vertex. To our knowledge this familial oculocutaneous condition, transmitted as an autosomal recessive trait, has not been reported previously.

Genetic linkage of cone-rod retinal dystrophy to chromosome 19q and evidence for segregation distortion

Inherited retinal dystrophies are the most common cause of childhood blindness in the developed world. Cone-rod retinal dystrophies are severe examples of this group of disorders. Analysis of a large cone-rod dystrophy pedigree suggested that inheritance within the family was influenced by meiotic drive (p = 0.008), a rare segregation distortion in human genetics. Two-point linkage analysis showed significant linkage with three markers mapping to chromosome 19q. Multipoint analysis gave a maximum lod score of 10.08 (theta = 0.05) distal to D19S47. Cone-rod dystrophy is therefore assigned to 19q13.1-q13.2 and a new candidate locus for other retinal dystrophies is identified.