An analysis of allelic variation in the ABCA4 gene.

PURPOSE: To assess the allelic variation of the ATP-binding transporter protein (ABCA4). METHODS: A combination of single-strand conformation polymorphism (SSCP) and automated DNA sequencing was used to systematically screen this gene for sequence variations in 374 unrelated probands with a clinical diagnosis of Stargardt disease, 182 patients with age-related macular degeneration (AMD), and 96 normal subjects. RESULTS: There was no significant difference in the proportion of any single variant or class of variant between the control and AMD groups. In contrast, truncating variants, amino acid substitutions, synonymous codon changes, and intronic variants were significantly enriched in patients with Stargardt disease when compared with their presence in subjects without Stargardt disease (Kruskal-Wallis P < 0.0001 for each variant group). Overall, there were 2480 instances of 213 different variants in the ABCA4 gene, including 589 instances of 97 amino acid substitutions, and 45 instances of 33 truncating variants. CONCLUSIONS: Of the 97 amino acid substitutions, 11 occurred at a frequency that made them unlikely to be high-penetrance recessive disease-causing variants (HPRDCV). After accounting for variants in cis, one or more changes that were compatible with HPRDCV were found on 35% of all Stargardt-associated alleles overall. The nucleotide diversity of the ABCA4 coding region, a collective measure of the number and prevalence of polymorphic sites in a region of DNA, was found to be 1.28, a value that is 9 to 400 times greater than that of two other macular disease genes that were examined in a similar fashion (VMD2 and EFEMP1).

A single EFEMP1 mutation associated with both Malattia Leventinese and Doyne honeycomb retinal dystrophy.

Malattia Leventinese (ML) and Doyne honeycomb retinal dystrophy (DHRD) refer to two autosomal dominant diseases characterized by yellow-white deposits known as drusen that accumulate beneath the retinal pigment epithelium (RPE). Both loci were mapped to chromosome 2p16-21 (refs 5,6) and this genetic interval has been subsequently narrowed. The importance of these diseases is due in large part to their close phenotypic similarity to age-related macular degeneration (AMD), a disorder with a strong genetic component that accounts for approximately 50% of registered blindness in the Western world. Just as in ML and DHRD, the early hallmark of AMD is the presence of drusen. Here we use a combination of positional and candidate gene methods to identify a single non-conservative mutation (Arg345Trp) in the gene EFEMP1 (for EGF-containing fibrillin-like extracellular matrix protein 1) in all families studied. This change was not present in 477 control individuals or in 494 patients with age-related macular degeneration. Identification of this mutation may aid in the development of an animal model for drusen, as well as in the identification of other genes involved in human macular degeneration.

Night blindness in Sorsby's fundus dystrophy reversed by vitamin A.

Sorsby's fundus dystrophy (SFD) is an autosomal dominant retinal degeneration caused by mutations in the tissue inhibitor of metalloproteinases-3 (TIMP3) gene. Mechanisms of the visual loss in SFD, however, remain unknown. In a SFD family with a novel TIMP3 point mutation, we tested a hypothesis that their night blindness is due to a chronic deprivation of vitamin A at the level of the photoreceptors caused by a thickened membrane barrier between the photoreceptor layer and its blood supply. Vitamin A at 50,000 IU/d was administered orally. Within a week, the night blindness disappeared in patients at early stages of disease. Nutritional night blindness is thus part of the pathophysiology of this genetic disease and vitamin A supplementation can lead to dramatic restoration of photoreceptor function.

Retinitis pigmentosa associated with a dominant mutation in codon 46 of the peripherin/RDS gene (arginine-46-stop).

PURPOSE: We identified genetic mutations and characterized their associated phenotypes in patients with retinitis pigmentosa. METHODS: Patients with retinitis pigmentosa were prospectively examined and screened for genetic mutations. RESULTS: A 46-year-old man with retinitis pigmentosa was found to have a heterozygous mutation in the peripherin/RDS gene (arginine-46-stop). He had late onset of symptoms and demarcated peripheral retinal atrophy. All five first-degree relatives including his parents had no detectable mutations or retinitis pigmentosa. Genotypic data were consistent with reported family structure. CONCLUSIONS: This study shows that new dominant mutations are a rare cause of isolated, or simplex, cases of retinitis pigmentosa. Identification of these mutations is helpful for genetic counseling.

Ocular findings associated with a Cys39Arg mutation in the Norrie disease gene.

OBJECTIVE: To diagnose the carriers and noncarriers in a family affected with Norrie disease based on molecular analysis. DESIGN: Family members from three generations, including one affected patient, two obligate carriers, one carrier identified with linkage analysis, one noncarrier identified with linkage analysis, and one female family member with indeterminate carrier status, were examined clinically and electrophysiologically. Linkage analysis had previously failed to determine the carrier status of one female family member in the third generation. Blood samples were screened for mutations in the Norrie disease gene with single-strand conformation polymorphism analysis. The mutation was characterized by dideoxy-termination sequencing. RESULTS: Ophthalmoscopy and electroretinographic examination failed to detect the carrier state. The affected individuals and carriers in this family were found to have a transition from thymidine to cytosine in the first nucleotide of codon 39 of the Norrie disease gene, causing a cysteine-to-arginine mutation. Single-strand conformation polymorphism analysis identified a patient of indeterminate status (by linkage) to be a noncarrier of Norrie disease. CONCLUSION: Ophthalmoscopy and electroretinography could not identify carriers of this Norrie disease mutation. Single-strand conformation polymorphism analysis was more sensitive and specific than linkage analysis in identifying carriers in this family.

Clinical features of a previously undescribed codon 216 (proline to serine) mutation in the peripherin/retinal degeneration slow gene in autosomal dominant retinitis pigmentosa.

BACKGROUND: Mutations in the human peripherin/retinal degeneration slow (rds) gene have been found in patients with macular dystrophies as well as in those with autosomal dominant retinitis pigmentosa. The authors studied the clinical features in members of two families with autosomal dominant retinitis pigmentosa and a previously unreported mutation in the peripherin/rds gene. METHODS: Affected family members underwent a clinical ophthalmic examination and electrophysiologic and psychophysical testing. Available family members were evaluated for a mutation in the peripherin/rds gene. RESULTS: A mutation in codon 216 of the peripherin/rds gene, resulting in a substitution of the amino acid serine for proline, was found to segregate with retinitis pigmentosa in these two families. Ocular features of this mutation include a later onset of more notable ophthalmoscopic, electrophysiologic, and psychophysical abnormalities of the retina, an atrophic-appearing foveal lesion, and extrafoveal atrophic and hyperpigmented degenerative retinal changes, which were found more posteriorly than usually seen in patients with retinitis pigmentosa. Visual field testing showed a partial ring scotoma or pear-shaped configuration of the remaining portions of the peripheral fields. CONCLUSION: A previously undescribed mutation in the peripherin/rds gene is responsible for an autosomal dominant retinitis pigmentosa phenotype. This phenotype tends to be associated with the development of an atrophic-appearing foveal lesion, more posterior distribution of pigmentary changes involving the vascular arcades, the presence of a partial ring scotoma or a pear-shaped configuration of the peripheral visual field, and a later onset of more extensive retinal structural and functional impairment.

Butterfly-shaped pigment dystrophy of the fovea caused by a point mutation in codon 167 of the RDS gene.

Butterfly-shaped pigment dystrophy of the fovea is an autosomal dominant eye disease characterized by a bilateral accumulation of yellowish or pigmented material at the level of the retinal pigment epithelium. It shares some clinical and histopathologic features with age related macular degeneration which is the most common cause of legal blindness in older patients. We screened affected patients from a three generation family with butterfly dystrophy for mutations in candidate genes. A base substitution was identified in the peripherin (RDS) gene and DNA sequencing revealed a G to A transition in codon 167 that substitutes aspartic acid for a highly conserved glycine. The mutation segregates with the disease phenotype (Zmax = 4, theta = 0) strongly suggesting that it causes the macular disease in this family.

Ocular findings associated with rhodopsin gene codon 267 and codon 190 mutations in dominant retinitis pigmentosa.

Two members of a family with autosomal dominant retinitis pigmentosa were found to have a cytosine-to-thymine mutation in the second nucleotide of codon 267 in the rhodopsin gene that resulted in a proline-to-leucine change. Two members of another family with autosomal dominant retinitis pigmentosa showed a guanine-to-thymine mutation in the first nucleotide of codon 190 in the rhodopsin gene that resulted in an aspartate-to-tyrosine change. Three members from a third family with autosomal dominant retinitis pigmentosa were also found to have a mutation in codon 190; however, this guanine-to-adenine mutation in the first nucleotide of codon 190 resulted in an aspartate-to-asparagine change. The relatively less severe functional retinal impairment in our patients with a transmembrane codon 267 rhodopsin gene mutation is generally comparable with that observed in a previously described codon 58 transmembrane mutation. The two families with different intradiscal codon 190 mutations showed a considerable difference in severity of their disease.