Late Onset Retinitis Pigmentosa

The spermatogenesis-associated protein-7 (SPATA7) gene - an overview

BACKGROUND

The spermatogenesis-associated protein-7 (SPATA7) gene encodes a ciliary protein that is expressed in the photoreceptors and in spermatocytes. Mutations in the SPATA7 gene are associated with congenital and early-onset forms of retinal dystrophy.

METHODS

Papers and review articles on SPATA7 were retrieved from the PubMed database using the search terms "SPATA7" and "spermatogenesis-associated protein 7". Those that were relevant to retinal disease or to the function of the SPATA7 gene were selected for review.

RESULTS

The SPATA7 locus was mapped as LCA3 to chromosome 14, and the gene identified by screening of all genes in the refined genomic interval. Mutations in SPATA7 are associated with Leber congenital amaurosis (LCA) and early-onset retinitis pigmentosa. There are no clear-cut correlations between the genotypes and phenotypes in SPATA7-associated disease, and phenotypic heterogeneity occurs among patients with the same mutation. The SPATA7 protein is expressed in the photoreceptor connecting cilia. Murine models of Spata7 knockout have been useful in understanding the role of this gene in the retina at the cellular and molecular levels.

CONCLUSION

Most of the mutations in the SPATA7 are nonsense or frameshifts and are predicted to lead to loss of function. Clinical heterogeneity is often seen in patients with SPATA7 mutations. Animal models of SPATA7 knockout indicate that the protein has a key role in organizing the ciliary protein complexes.

Prevalence, Age at Diagnosis, Mortality, and Cause of Death in Retinitis Pigmentosa in Korea-A Nationwide Population-based Study

PURPOSE

To determine the prevalence and mortality of retinitis pigmentosa (RP) patients in Korea.

DESIGN

Population-based retrospective cohort study.

METHODS

We used data covering the 2011-2014 period from the Rare Intractable Disease (RID) registry and Health Insurance Review and Assessment (HIRA) service, which include information on all patients diagnosed with RP based on predefined diagnostic criteria. Using the HIRA-RID database, we evaluated the prevalence and age at diagnosis of RP patients across the entire Korean population. We further linked the data from Statistics Korea to the HIRA-RID database to confirm mortality and causes of death.

RESULTS

The prevalence in the total population across all ages was 11.09 per 10⁵ people, and the prevalence in those over the age of 40 was 16.16 per 10⁵ people. The age at diagnosis ranged from 0 to 95 and, on average, was 44.8. The standardized mortality ratio (SMR) was 1.56 for all ages, peaking at 2.61 in men aged 40-59, which was attributed to 6.6-fold higher suicide rates than the same age group in the general male population.

CONCLUSIONS

This is the first nationwide epidemiologic study of RP patients covering the entire population of all ages. The results suggest that the prevalence of RP in Korea is about 1 in 9000 for all ages and 1 in 6000 for those over 40 years of age. The higher mortality of RP patients than that of the general population is attributable to a high suicide rate in male RP patients of working ages, which necessitates a careful attention to their mental health.

SPATA7: Evolving phenotype from cone-rod dystrophy to retinitis pigmentosa

BACKGROUND

SPATA7 mutations have been associated with different autosomal recessive retinal degeneration phenotypes. Long-term follow-up has not been described in detail.

MATERIALS AND METHODS

A Hispanic patient with SPATA7 mutations was evaluated serially over a 12-year period with kinetic and static chromatic perimetry, optical coherence tomography (OCT), and fundus autofluorescence (AF) imaging. Electroretinography (ERG) was performed at the initial visit.

RESULTS

The patient was homozygous for a mutation in SPATA7 (p.V458fs). At age 9, the ERG showed an abnormally reduced but preserved rod b-wave and no detectable cone signals. There were two islands of vision: a midperipheral island with greater cone than rod dysfunction and a central island with normal cone but no rod function. Serial measures of rod and cone vision and co-localized retinal structure showed that the midperipheral island slowly became undetectable. By age 21, only the central island and its cone function remained, but it had become more abnormal in structure and function.

CONCLUSION

The disease resulting from SPATA7 mutations in this patient initially presented as a cone-rod dystrophy (CRD), but changed over time into a phenotype more reminiscent of late-stage retinitis pigmentosa (RP). The differential diagnosis for both CRD and RP should include this rare molecular cause of autosomal retinal degeneration. An evolving phenotype complicates not only clinical diagnosis and patient counselling but also future strategies aimed at treating specific retinal regions.