Complex regulation of voltage-dependent activation and inactivation properties of retinal voltage-gated Cav1.4 L-type Ca2+ channels by Ca2+-binding protein 4 (CaBP4).

Cav1.4 L-type Ca(2+) channels are crucial for synaptic transmission in retinal photoreceptors and bipolar neurons. Recent studies suggest that the activity of this channel is regulated by the Ca(2+)-binding protein 4 (CaBP4). In the present study, we explored this issue by examining functional effects of CaBP4 on heterologously expressed Cav1.4. We show that CaBP4 dramatically increases Cav1.4 channel availability. This effect crucially depends on the presence of the C-terminal ICDI (inhibitor of Ca(2+)-dependent inactivation) domain of Cav1.4 and is absent in a Cav1.4 mutant lacking the ICDI. Using FRET experiments, we demonstrate that CaBP4 interacts with the IQ motif of Cav1.4 and that it interferes with the binding of the ICDI domain. Based on these findings, we suggest that CaBP4 increases Cav1.4 channel availability by relieving the inhibitory effects of the ICDI domain on voltage-dependent Cav1.4 channel gating. We also functionally characterized two CaBP4 mutants that are associated with a congenital variant of human night blindness and other closely related nonstationary retinal diseases. Although both mutants interact with Cav1.4 channels, the functional effects of CaBP4 mutants are only partially preserved, leading to a reduction of Cav1.4 channel availability and loss of function. In conclusion, our study sheds new light on the functional interaction between CaBP4 and Cav1.4. Moreover, it provides insights into the mechanism by which CaBP4 mutants lead to loss of Cav1.4 function and to retinal disease.

Clinical and Haplotypic Variability of Slovenian USH2A Patients Homozygous for the c. 11864G>A Nonsense Mutation.

PURPOSE: to determine a detailed clinical and haplotypic variability of the Slovenian USH2A patients with homozygous c.11864G>A (p.Trp3955Ter) nonsense mutation and to develop sensitive, accurate and rapid screening test. METHODS: Ten unrelated homozygous patients with detailed ophthalmological exam were included in our study. The High-Resolution Melting (HRM) method was developed for fast and reliable detection of the c.11864G>A mutation. RESULTS: The c.11864G>A mutation represents the vast majority of pathogenic alleles in Slovenian USH2A-Usher syndrome population (84%). The median age of onset of nyctalopia was 16 years and all patients younger than 40 years had hyperautofluorescent rings on fundus autofluorescence imaging. The Kaplan Meier survival analysis showed a decline of central vision after the age of 40, with 50% patients reaching visual acuity (VA) ≤ 0.05 at the average age of 66 years visual field diameter less than 20° at the average age of 59 years. There was a relatively large phenotypic variability in the retinal and audiological phenotype. Analysis of the p.Trp3955Ter-homozygous patients revealed four different haplotypes, with the frequency of the most common haplotype ~65%. Disease severity did not correlate with the haplotype. CONCLUSIONS: According to the natural history of homozygous p.Trp3955Ter patients any therapy aimed to slow disease progression in these patients would be best started before the age of 40. Phenotypic variability suggests the presence of cis and/or trans factors outside the USH2A gene that are able to affect disease severity. High frequency of p.Trp3955Ter mutation in Slovenian USH2A gene pool appears to be initiated from different unrelated founders because of migrations from neighboring populations. The mutation on haplotype 2 seems to be the major founder allele.

Night blindness during pregnancy and subsequent mortality among women in Nepal: effects of vitamin A and beta-carotene supplementation.

Night blindness due to vitamin A deficiency is common during pregnancy among women in Nepal. The authors assessed the risk of maternal death during and after a pregnancy with night blindness among women participating in a cluster-randomized, placebo-controlled vitamin A and beta-carotene supplementation trial in Nepal from July 1994 to September 1997. Subjects were 877 women with night blindness and 9,545 women without night blindness during pregnancy. Women were followed from the time they declared that they were pregnant through the end of the study, representing a median follow-up of 90 weeks (interquartile range: 64-121 weeks). Mortality of night-blind women in the placebo group was 3,601 per 100,000 pregnancies. In comparison, the relative risk of dying among nonnight-blind women in the placebo group was 0.26 (95% confidence interval (CI): 0.13, 0.55), and the relative risk among women with or without night blindness in the vitamin A/beta-carotene group was 0.32 (95% CI: 0.10, 0.91) and 0.18 (95% CI: 0.09, 0.36), respectively. Night-blind women were five times (95% CI: 2.20, 10.58) more likely to die from infections than were women who were not night blind. These findings show that night blindness during pregnancy is a risk factor of both short- and long-term mortality among women. Vitamin A/beta-carotene supplementation ameliorates this risk to a large extent.