Enhanced accumulation of A2E in individuals homozygous or heterozygous for mutations in BEST1 (VMD2).

Best vitelliform macular dystrophy (BMD) is an autosomal dominant inherited macular degenerative disease caused by mutations in the gene BEST1 (formerly VMD2). Prior reports indicate that BMD is characterized histopathologically by accumulation of lipofuscin in the retinal pigment epithelium (RPE). However, this accumulation has not been quantified and the chemical composition of lipofuscin in BMD has not been examined. In this study we characterize the histopathology of a donor eye from a rare individual homozygous for a mutation (W93C) in BEST1. We find that this individual's disease was not any more severe than has been described for heterozygotes. We then used this tissue to quantify lipofuscin accumulation by enriching intracellular granules from RPE cells on sucrose gradients and counting the granules in each density fraction. Granules from the homozygous donor eye as well as a donor eye from an individual heterozygous for the mutation T6R were compared with age-matched control eyes. Interestingly, the least dense fraction, representing classical lipofuscin granules was either not present or significantly diminished in the BMD donor eyes and the autoflourescence associated with lipofuscin had shifted to denser fractions. However, a substantial enrichment for granules in fractions of higher density was also noted in the BMD samples. Inspection of granules from the homozygous donor eye by electron microscopy revealed a complex abnormal multilobular structure. Analysis of granules by HPLC indicated a approximately 1.6- and approximately fourfold overall increase in A2E in the BMD eyes versus age-matched control eyes, with a shift of A2E to more dense granules in the BMD donor eyes. Despite the increase in A2E and total intracellular granules, the RPE in the homozygous donor eyes was relatively well preserved. Based on these data we conclude that the clinical and histopathologic consequences to the homozygous donor were not any more severe than has been reported previously for individuals who are established or presumptive heterozygotes. We find that A2E is a component of the lipofuscin accumulated in BMD and that it is more abundant than in control eyes suggesting that the etiology of BMD is similar to Stargardt's disease and Stargardt-like macular dystrophy. Finally, the changes we observe in the granules suggest that the histopathology and eventual vision loss associated with BMD may be due to defects in the ability of the RPE to fully degrade phagocytosed photoreceptor outer segments.

Best's vitelliform macular dystrophy caused by a new mutation (Val89Ala) in the VMD2 gene.

PURPOSE: To describe the clinical phenotype in a family with Best's vitelliform macular dystrophy (BMD) and a new mutation (Val89Ala) in the VMD2 gene. METHODS: The genotype was determined by direct sequence analysis of the individual exons of VMD2. Nine members of a family with BMD were examined. The examination included best-corrected visual acuity, electro-oculography (EOG), fundus examination, and photography. Four of the patients were also examined with full-field ERG and three with multifocal ERG. RESULTS: A T-to-C substitution was identified at position 370 in the cDNA of VMD2, leading to a Val89Ala change in the protein. Six patients, five with the Val89Ala mutation and a nine-year-old boy without the mutation, presented with a pathological Arden ratio on EOG examination. Most of the patients with BMD in this family had an onset of visual failure by the age of 40-50 years. The older patients in the family demonstrated atrophic macular dystrophy. CONCLUSIONS: Patients with BMD and the Val89Ala mutation in the VMD2 gene can present with a phenotype of a mostly late-onset visual failure. These BMD patients, who present with visual failure and macular degeneration in middle age, can be misdiagnosed as being affected with adult-onset macular dystrophies instead of BMD, because the latter is often regarded as a disease of childhood and adolescence.

The mutation spectrum of the bestrophin protein--functional implications.

Best's macular dystrophy (BMD), also known as vitelliform macular degeneration type 2 (VMD2; OMIM 153700), is an autosomal dominant form of macular degeneration with mainly juvenile onset. BMD is characterized by the accumulation of lipofuscin within and beneath the retinal pigment epithelium. The gene causing the disease has been localized to 11q13 by recombination breakpoint mapping. Recently, we have identified the causative gene encoding a protein named bestrophin, and mutations have been found mainly to affect residues that are conserved from a family of genes in Caenorhabditis elegans. The function of bestrophin is so far unknown, and no reliable predictions can be made from sequence comparisons. We have investigated the bestrophin gene in 14 unrelated Swedish, Dutch, Danish, and Moroccan families affected with BMD and found eight new mutations. Including the previously published mutations, 15 different missense mutations have now been detected in 19 of the 22 families with BMD investigated by our laboratory. Interestingly, the mutations cluster in certain regions, and no nonsense mutations or mutations causing frame-shifts have been identified. Computer simulations of the structural elements in the bestrophin protein show that this protein is probably membrane bound, with four putative transmembrane regions.

Clinical expression of Best's vitelliform macular dystrophy in Swedish families with mutations in the bestrophin gene.

OBJECTIVE: To examine the clinical phenotype of three Swedish families with Best's vitelliform macular dystrophy (BMD) and three different mutations in the recently identified bestrophin gene. METHODS: Three families, including 13 patients, were examined clinically using visual acuity testing, electro-oculography, fundus inspection, and fundus photography. The mutations were previously determined by direct sequence analysis of the individual exons in the bestrophin gene. RESULTS: The largest family (SL76), with the Y85K (T357C) mutation in the bestrophin gene, demonstrated a clinical phenotype characterized by a variable degree of visual acuity reduction and a marked intrafamilial variability in macular pathology. The electro-oculograms, however, demonstrated similar results in all patients regardless of the severity of the macular dysfunction. The smallest family (SL3), with the mutation V9A (T130C) in the bestrophin gene, and the family (SL2) with the mutation D104E (C416A) demonstrated a similar clinical phenotype. The majority of patients (11/13 examined subjects) had a binocular visual acuity of 20/63 or better at a late stage of the disease course, indicating a relatively good prognosis for visual acuity in this specific phenotype. The ophthalmoscopic changes were followed in one of the patients for 38 years and in three of the patients for 19 years and showed that the macular appearance seems to be stable after adolescence. CONCLUSIONS: Patients with BMD and mutations in the bestrophin gene have a similar clinical phenotype characterized by a variable, but relatively moderate visual acuity reduction, atrophic changes in the macula, and pathological results of the electro-oculograms. The macular appearance remains essentially unchanged through the atrophic stage (stage IV) in the majority of patients, indicating a stationary disease course associated with this specific genotype.

Identification of the gene responsible for Best macular dystrophy.

Best macular dystrophy (BMD), also known as vitelliform macular dystrophy (VMD2; OMIM 153700), is an autosomal dominant form of macular degeneration characterized by an abnormal accumulation of lipofuscin within and beneath the retinal pigment epithelium cells. In pursuit of the disease gene, we limited the minimum genetic region by recombination breakpoint analysis and mapped to this region a novel retina-specific gene (VMD2). Genetic mapping data, identification of five independent disease-specific mutations and expression studies provide evidence that mutations within the candidate gene are a cause of BMD. The 3' UTR of the candidate gene contains a region of antisense complementarity to the 3' UTR of the ferritin heavy-chain gene (FTH1), indicating the possibility of antisense interaction between VMD2 and FTH1 transcripts.

Anticipation of autosomal dominant progressive external ophthalmoplegia with hypogonadism.

A large Swedish family with members affected by progressive external ophthalmoplegia with hypogonadism were followed-up and reviewed. Hypogonadism included delayed sexual maturation, primary amenorrhea, early menopause, and testicular atrophy. Cataracts, cerebellar ataxia, neuropathy, hypoacusia, pes cavus, tremor, parkinsonism, depression, and mental retardation were other features observed in this family. Muscle biopsy samples of advanced cases showed ragged-red fibers, focal cytochrome c oxidase deficiency, and multiple mtDNA deletions by Southern blot analysis. An autosomal dominant mode of inheritance was evident with anticipation in successive generations. Linkage analysis excluded the chromosome 10q23.3-q24.3 region reported as being linked to the disease in a Finnish family with autosomal dominant progressive external ophthalmoplegia. We report for the first time clinical evidence for anticipation in a family with autosomal dominant progressive external ophthalmoplegia. We hypothesize that the nuclear gene causing this enigmatic disorder may be directly influenced by an expansion of an unstable DNA sequence and that the resulting phenotype is caused by a concerted action with multiple deletions of mtDNA.