Genetics and Disease Expression in the CNGA3 Form of Achromatopsia: Steps on the Path to Gene Therapy.

PURPOSE: Achromatopsia (ACHM) is a congenital, autosomal recessive retinal disease that manifests cone dysfunction, reduced visual acuity and color vision, nystagmus, and photoaversion. Five genes are known causes of ACHM. The present study took steps toward performing a trial of gene therapy in ACHM by characterizing the genetics of ACHM in Israel and the Palestinian Territories and analyzing retinal function and structure in CNGA3 ACHM patients from the Israeli-Palestinian population and US patients with other origins. DESIGN: Case series study. PARTICIPANTS: Patients with clinically suspected ACHM, cone dysfunction phenotypes, and unaffected family members were included. The protocol was approved by the local institutional review board and informed consent was obtained from all participants. METHODS: Genetic analyses included homozygosity mapping and exome sequencing. Phenotype was assessed with electroretinography (ERG), optical coherence tomography, psychophysics, and photoaversion testing. MAIN OUTCOME MEASURES: Single nucleotide polymorphism microarray, exome analysis, DNA sequence analysis, visual function testing including ERG, and photoaversion. RESULTS: We identified 148 ACHM patients from 57 Israeli and Palestinian families; there were 16 CNGA3 mutations (5 novel) in 41 families and 5 CNGB3 mutations (1 novel) in 8 families. Two CNGA3 founder mutations underlie >50% of cases. These mutations lead to a high ACHM prevalence of ∼1:5000 among Arab-Muslims residing in Jerusalem. Rod ERG abnormalities (in addition to cone dysfunction) were detected in 59% of patients. Retinal structure in CNGA3 ACHM patients revealed persistent but abnormal foveal cones. Under dark- and light-adapted conditions, patients use rod-mediated pathways. Photoaversion was readily demonstrated with transition from the dark to a dim light background. CONCLUSIONS: Among Israeli and Palestinian patients, CNGA3 mutations are the leading cause of ACHM. Retinal structural results support the candidacy of CNGA3 ACHM for clinical trials for therapy of cone photoreceptors. Efficacy outcome measures would include chromatic light-adapted psychophysics, with attention to the photoreceptor basis of the response, and quantitation of photoaversion.

Identification of mutations causing inherited retinal degenerations in the israeli and palestinian populations using homozygosity mapping.

PURPOSE: The Israeli and Palestinian populations are known to have a relatively high level of consanguineous marriages, leading to a relatively high frequency of autosomal recessive (AR) diseases. Our purpose was to use the homozygosity mapping approach, aiming to prioritize the set of genes and identify the molecular genetic causes underlying AR retinal degenerations in the Israeli and Palestinian populations. METHODS: Clinical analysis included family history, ocular examination, full-field electroretinography (ERG), and funduscopy. Molecular analysis included homozygosity mapping and mutation analysis of candidate genes. RESULTS: We recruited for the study families with AR nonsyndromic retinal degenerations, including mainly retinitis pigmentosa (RP), cone-rod degeneration (CRD), and Leber congenital amaurosis (LCA). With the aim to identify the causative genes in these families, we performed homozygosity mapping using whole genome single nucleotide polymorphism (SNP) arrays in 125 families. The analysis revealed the identification of 14 mutations, 5 of which are novel, in 16 of the families. The mutations were identified in the following eight genes: RDH12, PROM1, MFRP, TULP1, LCA5, CEP290, NR2E3, and EYS. While most patients had a retinal disease that is compatible with the causing gene, in some cases new clinical features are evident. CONCLUSIONS: Homozygosity mapping is a powerful tool to identify genetic defects underlying heterogeneous AR disorders, such as RP and LCA, in consanguineous and nonconsanguineous patients. The identification of significant and large homozygous regions, which do not include any known retinal disease genes, may be a useful tool to identify novel disease-causing genes, using next generation sequencing.

Cone dystrophy with supernormal rod response: novel KCNV2 mutations in an underdiagnosed phenotype.

OBJECTIVE: To study the clinical variability and KCNV2 mutation spectrum in cone dystrophy with supernormal rod response (CDSRR) in the Israeli population. DESIGN: Case series. PARTICIPANTS: Patients with cone-dominated diseases and unaffected relatives were included. The protocol was approved by the institutional review board and informed consent was obtained from all participants. METHODS: Genomic DNA was extracted and Sanger sequencing was performed on polymerase chain reaction products. Whole genome single nucleotide polymorphism analysis was performed using Affymetrix (Santa Clara, CA) platforms. MAIN OUTCOME MEASURES: Single nucleotide polymorphism microarray and homozygosity analysis, DNA sequence analysis, visual function testing, and electroretinography. RESULTS: Aiming to study the genetics of inherited retinal degenerations in the Israeli and Palestinian populations, we recruited 220 index cases with cone-dominated diseases, of which 2 carried the clinical diagnosis of CDSRR. Mutation screening of KCNV2 revealed 2 compound heterozygous mutations in 2 affected sisters in 1 family and a homozygous mutation in the other family. Inquiring whether KCNV2 is the cause of disease in the remaining patients with cone-dominated diseases, we performed whole genome homozygosity mapping in 52 consanguineous families (of the initial 220), 2 of which had homozygous regions encompassing KCNV2. Mutation analysis revealed a different homozygous mutation in each family. In addition, KCNV2 was screened in 4 families in which review of the clinical data suggested CDSRR misdiagnosis. The analysis revealed 2 compound heterozygous mutations in 1 family. After the genetic analysis and the review of the clinical findings, the diagnosis was revised to CDSRR in all patients with KCNV2 mutations. Clinical data of 13 KCNV2 patients suggested that, although in some cases the classic phenotype of CDSRR was present, others may have dark-adapted electroretinographic responses that are within normal range. The delay in dark-adapted responses may be a more reliable indicator. CONCLUSIONS: This is the first report of genetic and clinical analysis of CDSRR in the Israeli population leading to the identification of 4 novel KCNV2 mutations. Our results support recent studies showing that CDSRR can be misdiagnosed, and therefore screening of KCNV2 for mutations should be considered in patients with cone-dominated diseases, particularly when dark-adapted responses are delayed.

Refractive profile in oculocutaneous albinism and its correlation with final visual outcome.

PURPOSE: To evaluate the prevalence of refractive errors in different subtypes of oculocutaneous albinism, and to see if there is any correlation between refractive errors and final visual outcome in this population. PATIENTS/METHODS: This is a retrospective study of 132 albino patients, ranging in age from 0.5 to 35 years. They were divided into four subtypes: OCA1A, OCA1B and OCA1C, and OCA2. Refractive errors were evaluated objectively by cycloplegic refraction and subjectively in cooperative patients. Best corrected visual acuity was assessed binocularly. Refractive errors were divided into three groups--hypermetropia, myopia and astigmatism--to avoid the use of spherical equivalent. RESULTS: Refractive errors were mainly astigmatism and hypermetropia. The OCA1A group showed high hypermetropia (≥ 5 dioptres) in 43.4% of patients, reaching significantly higher levels than in other subgroups (p=0.007). Mean visual acuity in logMAR was: OCA1A=0.81, OCA1B=0.64, OCA1C=0.61 and OCA2=0.48. Astigmatism averaged 2.1 dioptres (consistently with-the-rule), and it was homogeneously distributed between all subgroups (53%). CONCLUSIONS: The poorest visual acuity was found in those with OCA1A, which was associated with the highest rate of high hypermetropia (statistically significant different from other subgroups). Astigmatism was the most common visually significant refractive error across all subtypes of albinism. These results may help to clarify the prevalence of refractive errors in albino patients and aid the prediction of visual outcome in this heterogeneous population.

Prenatal molecular diagnosis of oculocutaneous albinism (OCA) in a large cohort of Israeli families.

OBJECTIVES: To present our accumulated data on prenatal molecular diagnosis of oculocutaneous albinism (OCA) in a large cohort of Israeli albino families. METHODS: Albinism consists of variable phenotypes, but only families with predicted severely handicapped albino offspring, who declared their wish to terminate a pregnancy of such a fetus, are eligible for prenatal testing. Prenatal testing is not offered otherwise. Following detailed genetic investigation and counseling, molecular prenatal testing was performed using the combination of mutation screening, direct sequencing, and haplotype analysis. RESULTS: A total of 55 prenatal tests were performed in 37 families; in 26 families the propositus was the child, and in 11, a parent or a close relative. In 32 families tyrosinase (TYR) mutations were diagnosed. In 5 families a P gene mutation was detected. Twelve albino fetuses were diagnosed. Following further genetic counseling, all couples elected to terminate the pregnancy. Three additional pregnancies were terminated for other reasons. CONCLUSIONS: Families with increased risk for an albino child with severe visual handicap, seek premarital and prenatal genetic counseling and testing, for the prevention of affected offspring. Our combined methods of molecular genetic testing enable a nationwide approach for prevention of albinism. The same paradigm can be applied to other populations affected with albinism.