Ординатура / Офтальмология / Английские материалы / Recent Advances in Retinal Degeneration_LaVail, Hollyfield, Anderson _2008

Fig. 1 Pedigree and haplotype diagram. Black squares indicate individuals affected with CSNB1. Circles with a central black dot indicate carriers. Black bars represent the disease allele inherited from ancestor. White bars represent normal allele. Arrow indicates proband

elucidated that: (1) all affected individual was male; (2) no father-son transmission;

(3) none of the parents of affected individual was affected. These features strongly suggest that the condition is inherited as an X-linked recessive trait. Females (ID 5,7,9,11,12,16) with affected sons and daughter (ID 28) with affected father must be obligate carriers.

Table 1 Clinical data of available individuals in this CSNB family

3.2 Clinical Results

The manifest refraction was –9.00 D or lower (spherical equivalent) in affected GFP-positive when the mice were injected at E14.5. It is unknown why certain cells would be adults, with BCVA less than 20/25. Funduscopic observation of all affected individuals revealed myopic fundus changes typical of high myopia with optic nerve head crescent and “tigroid” appearance of posterior retina. Such fundus changes and high myopia were not observed in unaffected individuals and obligate carriers except one who had high myopic changes in one eye (ID 12). The axial length of the proband was 25.22 mm (OD) and 24.97 mm (OS) at 8 years old. One (ID 17) in five patients complained of impaired night vision and there was no suggestion of a night vision problem in the rest.

3.3 Electroretinogram

ERG recordings under ISCEV of the proband and his uncle (ID 17) demonstrated that the rod ERG was absent; the mixed rod-cone response elicited by a single bright flash had a negative configuration with normal a-wave amplitude and reduced b-wave amplitude; the OPs were absent; the cone and 30Hz flicker ERGs appear nearly normal except the a-wave of the cone ERG has a plateau-like flat bottom. The ERG results of the proband’s mother revealed no abnormality (Fig. 2).

Fig. 2 ERG recording under ISCEV conditions for the proband. Changes typical of CSNB1 are shown: the rod ERG is absent. The mixed rod-cone response elicited by a single bright flash has a negative configuration. The OPs are absent. The cone and 30Hz flicker ERGs appear nearly normal

3.4 Linkage Analysis

Two point linkage analysis yielded positive lod scores with five of the six selected markers on Xp11.4 (DXS8012, DXS8035, DXS8083, DXS1208, DXS1204), with DXS8035 showing the highest lod score of 2.23 for at theta=0 (Table 2). Haplotypes of markers in this region support the linkage results. The haplotype “361223” was co-segregated with affected family member (Fig. 1).

3.5 Mutation Analysis

Mutation screening by direct sequencing in affected male identified a novel A-to-C transversion in exon 2, resulting in a change ACG of Threonine to Proline at codon 258. Obligate carriers carried a heterozygous A-to-C. Neither normal subject of the family nor 110 ethnically matched controls show this mutation (Fig. 3).

4 Discussion

CSNB is a genetically and clinically heterogeneous nonprogressive retinal disorder. Ten loci with ten genes have been implicated in CSNB, including GNAT1, PDE6B,

Fig. 3 Sequence results of the NYX gene fragments in normal controls, patients and carriers. At cDNA 772 Adenosine is changed to Cytosine, the encoded amino acid is changed from Threonine to Proline. All female carriers are heterozygous

RHO, GRK1, GRM6, RDH5, SAG, CACNA1F, NYX, and RPGR. Based fundamentally on the ERG findings, XLCSNB can be divided into complete (CSNB1) characterized by absent rod system function and incomplete (CSNB2) with evidence of rod function.

X-linked CSNB is not readily identified clinically owing to the lack of specificity of the main clinical features. Patients with complete X-linked CSNB usually have high myopia with a tigroid-appearing fundus and tilted myopic disc and some patients have mild nystagmus. In this report, all affected males had high myopia but only one complained of night-blindness. Miyake reported (Miyake, 2006a) that 15/49 complete XLCSNB and 1/41 incomplete XLCSNB patients had history of impaired night vision. Therefore, clinicians must be cautious when diagnosing CSNB relying on history of night blindness. In our electrically illuminated night-time environment, people can be unaware of loss of night vision because night-time activities are typically done with sufficient light. Another contributing factor of misdiagnosis of CSNB is its absence of a clinical identifiable structural abnormality. However, the shape of ERGs is extremely uniform for CSNB1 patients with the scotopic b-wave evoked by dim flashes and the early oscillatory potential wavelets unrecordable and the photopic system nearly normal. The correct diagnosis of CNSB1 is not easy unless ERG performed. Carrier states of CSNB1 with selectively reduced Ops have been reported (Miyake, 2006b ), the obligate carrier (ID 16) in this study didn’t show ERG anomalies. One eye with high myopia in one obligate carrier (ID 12) may be associated with special X inactivation.

Two causative genes for XLCSNB have been identified through positional cloning. CACNA1F (encoding a calcium channel α1-subunit) is mutated in CSNB2 patients and is localized in Xp11.23 (Bech-Hansen et al., 1998; Strom et al., 1998). The gene responsible for CSNB1, NYX encodes a protein of 481 amino acids containing an N-terminal signal peptide and a C-terminal GPI anchor. The central part of the polypeptide encodes 11 consecutive LRRs (Leucine Rich Repeats), which are flanked by N- and C-terminal cysteine-rich LRRs (Bech-Hansen et al., 2000; Pusch et al., 2000). According to the cysteine pattern (C’CxC(9x)C), nyctalopin belongs to the class II small leucine-rich proteoglycans (Zeitz et al., 2003). LRRs are suggested to mediate protein-protein interaction (Kobe and Deisenhofer, 1994).

The role of NYX in the pathogenesis of CSNB1 is not clear. CSNB1 is characterized by the absence of post-receptor rod-mediated function (Miyake et al., 1986). This information suggests a defect in synaptic transmission between photoreceptor and second-order neurons.The presence of a subnormal photopic ON response suggests an additional effect on the cone photoreceptor-ON bipolar pathway but no apparent effect on the cone OFF bipolar response. Defective NYX gene product prevents detectable signal transmission through ON rod bipolar cells, but there is a residual transmission through rod–cone gap junctions in CSNB1, possibly through the OFF cone pathway (Scholl et al., 2001). Recently, Morgans et al. demonstrated that the nyctalopin was associated with the synapses of both rod and cone terminals and with rod bipolar cell terminals of mammalian retina. This supports a role for nyctalopin in the synaptic transmission and/or synapse formation in the retina (Morgans et al., 2006).

Fig. 4 3D structure of nyctalopin. The novel mutation T258P was shown with asterisk

In this study, we confirm the diagnosis of CSNB1 in a Chinese family by combined clinical and genetic investigation. A novel T258P mutation was identified related to this phenotype. Including this one, 40 mutations in NYX have been reported among CSNB1 patients (www.hgmd.org). More than 50% of them are missense mutations and 80% missense mutations present in LRR. Each LRR is thought to form a β-sheet and an α-helix. The mutation we found is in the 9th LRR, which is a β-sheet by 3D protein structure modeling using Cn3D (Fig. 4). The substitution is predicted to interfere the formation of β-sheet that would possibly disturb the structural stability and function of nyctalopin.

Acknowledgments We thank all patients and family members for their participation. This study was supported in part by the National 863 Plan of China (2002BA711A08 to R.S.) and Beijing science and technology project (H020220020510 to R.S.)

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10q26 Is Associated with Increased Risk

of Age-Related Macular Degeneration in the Utah Population

D. Joshua Cameron, Zhenglin Yang, Zhongzhong Tong, Yu Zhao, Alissa Praggastis, Eric Brinton, Jennifer Harmon, Yali Chen, Erik Pearson, Paul S. Bernstein, Gregory Brinton, Xi Li, Adam Jorgensen, Sara Schneider, Daniel Gibbs, Haoyu Chen, Changguan Wang, Kimberly Howes, Nicola J. Camp, and Kang Zhang

1 Introduction

Age-related macular degeneration (AMD) includes a wide range of phenotypes. Early AMD is mainly characterized by the presence of soft dusen in the macula without visual loss, while advanced AMD is characterized by geographic atrophy (GA or dry AMD) and neovascular AMD (wet AMD) with visual loss. Despite the rising prevalence of AMD as a result of increasing life expectancy, its underlying etiology is poorly understood and there is no specific therapy. Nutritional supplements and antagonists of vascular endothelial growth factor (VEGF) have been reported to halt the progression of visual loss in wet AMD (Bressler et al., 1988). Wet AMD is usually associated with an aggressive form of visual loss due to choroidal neovascularization (CNV).

Previous reports by several groups have identified a significant association between a common missense variant (Y402H) and non-coding variants in CFH and AMD in the United States (Edwards et al., 2005; Fisher et al., 2005; Hageman et al., 2005; Haines et al., 2005; Klein et al., 2005; Li et al., 2006; Maller et al., 2006) and Europe (Fisher et al., 2005; Souied et al., 2005; Despriet et al., 2006; Magnusson et al., 2006; Postel et al., 2006; Sepp et al., 2006; Simonelli et al., 2006). Recently, it was reported that rs10490924 in LOC387715 is the second major locus for AMD located at 10q locus (Conley et al., 2005; Rivera et al., 2005; Haddad et al., 2006; Maller et al., 2006; Schmidt et al., 2006). In this study we performed an association study incorporating SNP data for LOC387715 and PLEKHA1 at 10q26 and for CFH at 1q31.3 in the Utah AMD cohort. Our results support previous findings that

D.J. Cameron

Department of Ophthalmology and Visual Sciences, Moran Eye Center and Program in Human Molecular Biology and Genetics, University of Utah School of Medicine, Salt Lake City, UT 84132, Tel: 801-363-2433

e-mail: joshua.cameron@utah.edu

Table 1 Association results for three SNPs at 10q26.13 and CFH in wet AMD Cases and Controls

results were highly significant, with rs10490924 associated with the highest risk (p=1.0×10–9) and the largest difference in allele frequency for the risk allele (T: 39.7% versus 24.7%, P =4.5×10–9). A clear dose effect for the risk allele, T, was observed, with individuals heterozygous for rs10490924 showing a 1.70-fold increased risk (95% CI: 1.18, 2.44) and a 7.09-fold increased risk with TT homozygotes (95% CI: 3.67, 13.70), to develop wet AMD (Table 1). The PAR for this locus is estimated to be 39%. Details for the association with CFH in the Utah cohort were previously reported (Magnusson et al., 2006).

In agreement with previous reports (Conley et al., 2005; Rivera et al., 2005), we found a major association for 10q26 at LOC387715 rs10490924. To investigate this further, we performed two separate association analyses for PLEKHA1 rs2421016 and PLEKHA1 rs4146894 conditional on genotype at LOC387715 rs10490924. No significant association was found for either PLEKHA1 SNP conditional on genotypes GG or TT at LOC388715 rs10490924. There is substantial and highly significant LD between rs10490924 and rs2421016 (D’ = 0.53, p = 1.2×10–17) and rs4146894 (D’ = 0.53, p = 2.4×10–18) in AMD cases, and this appears to drive associations. However, some marginal significance is still observed for both PLEKHA1 variants when LOC388715 rs10490924 is GT. Such a result is consistent with a disease haplotype upon which all three variants lie.

We constructed a putative disease haplotype using multiple SNPs spanning this region. An extended disease haplotype TTTACT defined by SNPs rs4146894, rs2421016, rs10490924, rs3750847, rs2014307, rs2248799 showed the strongest

Table 2 Conditional association for rs10490924 on genotype at C F H rs1061170