Two novel mutations in the bestrophin-1 gene and associated clinical observations in patients with best vitelliform macular dystrophy

A novel mutation of BEST1 gene in Best disease

PURPOSE

To describe a new genetic variation of BEST1 gene in Best vitelliform macular dystrophy.

METHODS

A patient with bilateral multiple retinal yellowish lesions at the posterior pole underwent fluorescein angiography, fundus autofluorescence, optical coherence tomography, electrooculogram and blood sample for genetic testing.

RESULTS

A diagnosis of a Best vitelliform macular dystrophy was made. Heterozygous mutation c.76G > A (p.Gly26Ser) in exon 2 of the BEST1 gene was found.

CONCLUSION

These findings contribute to expand the mutation spectrum of BEST1 gene.

"Novel p.Tyr284Cys BEST1 genotype-phenotype correlations of Vitelliform Macular Dystrophy in a family with incomplete penetrance"

Purpose: Vitelliform Macular Dystrophy is an inherited autosomal dominant disease with variable expressivity, caused by a mutation in the BEST1 gene. We report a family with variable expressivity and incomplete penetrance in its members.Materials and Methods: A Mexican family was studied. It was comprised of six individuals (father, mother, and four children). A clinical history was taken, and a complete ophthalmological examination (distance best-corrected visual acuity, slit-lamp biomicroscopy, optical coherence tomography, fundus autofluorescence, optical coherence tomography angiography, and electrophysiological studies) was performed in each individual.Results: Two members presented low visual acuity and vitelliform lesions in different stages in the ocular fundus. The assessment suggested a diagnosis of Vitelliform Macular Dystrophy. Genetic analysis was performed by sequencing of exons 2, 4, 5, 7, 8, and 9 of the BEST1 gene. All patients were carriers of the A variant allele of SNP rs1109748 located in exon 2 (c.219 C > A; p.Ile73=). Also, a missense mutation was identified in exon 7 in the mother and two children (c.851A>G; p.Tyr284Cys). The mother has a normal visual acuity, no abnormal findings in the ophthalmological examination and an abnormal electrooculogram, exhibiting incomplete penetrance.Conclusion: This represents one of the few cases of Vitelliform Macular Dystrophy with incomplete penetrance, being the first in our country and Latin America, and with our reported mutation with this characteristic.

An allosteric mechanism of inactivation in the calcium-dependent chloride channel BEST1

Bestrophin proteins are calcium (Ca²⁺)-activated chloride channels. Mutations in bestrophin 1 (BEST1) cause macular degenerative disorders. Whole-cell recordings show that ionic currents through BEST1 run down over time, but it is unclear whether this behavior is intrinsic to the channel or the result of cellular factors. Here, using planar lipid bilayer recordings of purified BEST1, we show that current rundown is an inherent property of the channel that can now be characterized as inactivation. Inactivation depends on the cytosolic concentration of Ca²⁺, such that higher concentrations stimulate inactivation. We identify a C-terminal inactivation peptide that is necessary for inactivation and dynamically interacts with a receptor site on the channel. Alterations of the peptide or its receptor dramatically reduce inactivation. Unlike inactivation peptides of voltage-gated channels that bind within the ion pore, the receptor for the inactivation peptide is on the cytosolic surface of the channel and separated from the pore. Biochemical, structural, and electrophysiological analyses indicate that binding of the peptide to its receptor promotes inactivation, whereas dissociation prevents it. Using additional mutational studies we find that the "neck" constriction of the pore, which we have previously shown to act as the Ca²⁺-dependent activation gate, also functions as the inactivation gate. Our results indicate that unlike a ball-and-chain inactivation mechanism involving physical occlusion of the pore, inactivation in BEST1 occurs through an allosteric mechanism wherein binding of a peptide to a surface-exposed receptor controls a structurally distant gate.

Genetic variations in Bestrophin‑1 and associated clinical findings in two Chinese patients with juvenile‑onset and adult‑onset best vitelliform macular dystrophy

Best vitelliform macular dystrophy (BVMD) is a hereditary retinal disease characterized by the bilateral accumulation of large egg yolk‑like lesions in the sub‑retinal and sub‑retinal pigment epithelium spaces. Macular degeneration in BVMD can begin in childhood or adulthood. The variation in the age of onset is not clearly understood. The present study characterized the clinical characteristics of two Chinese patients with either juvenile‑onset BVMD or adult‑onset BVMD and investigated the underlying genetic variations. A 16‑year‑old male (Patient 1) was diagnosed with juvenile‑onset BVMD and a 43‑year‑old female (Patient 2) was diagnosed with adult‑onset BVMD. Comprehensive ophthalmic examinations were performed, including best‑corrected visual acuity, intraocular pressure, slit‑lamp examination, fundus photography, optical coherence tomography, fundus fluorescein angiography imaging and Espion electrophysiology. Genomic DNA was extracted from peripheral blood leukocytes collected from these patients, their family members, and 200 unrelated subjects within in the same population. The 11 exons of the bestrophin‑1 (BEST1) gene were amplified by polymerase chain reaction and directly sequenced. Both patients presented lesions in the macular area. In Patient 1, a heterozygous mutation c.903T>G (p.D301E) in exon 8 of the BEST1 gene was identified. This mutation was not present in any of the unaffected family members or the normal controls. Polymorphism phenotyping and the sorting intolerant from tolerant algorithm predicted that the amino acid substitution D301E in bestrophin‑1 protein was damaging. In Patient 2, a single nucleotide polymorphism c.1608C>T (p.T536T) in exon 10 of the BEST1 gene was identified. These findings expand the spectrum of BEST1 genetic variation and will be valuable for genetic counseling and the development of therapeutic interventions for patients with BVMD.

Bestrophin 1 gene analysis and associated clinical findings in a Chinese patient with Best vitelliform macular dystrophy

The aim of the present study was to investigate the clinical characteristics and the underlying genetic causes of Best vitelliform macular dystrophy (BVMD) in a sporadic case in a Chinese patient. A 10‑year‑old boy was diagnosed with BVMD; complete ophthalmic examinations were performed, including best‑corrected visual acuity, intraocular pressure, slit‑lamp examination, fundus photograph, optical coherence tomography and fundus fluorescein angiography imaging. Genomic DNA was extracted from leukocytes of the peripheral blood collected from this patient and his family members. DNA samples from 200 unrelated subjects from the Chinese population were used as controls. A total of 11 exons of the bestrophin 1 (BEST1) gene were amplified by polymerase chain reaction and directly sequenced. The results revealed that the patient presented with yellowish lesions in the macular area. Heterozygous mutations c.292G>A (p.Glu98Lys) in exon 4 and c.1608C>T (p.Thr536Thr) in exon 10 of the BEST1 gene were identified in this sporadic case; however, this was not identified in any of his unaffected family members or in the normal controls. The c.292G>A (p.Glu98Lys) mutation has not been previously reported, whereas the c.1608C>T (p.Thr536Thr) mutation is a previously characterized single nucleotide polymorphism (SNP). In conclusion, BEST1 gene mutations and polymorphisms have been reported in diverse ethnic groups, and the present study identified a novel BEST1 gene mutation and an SNP that occurred simultaneously in a Chinese patient with BVMD.

Two heterozygous mutations identified in one Chinese patient with bilateral macular coloboma

Congenital macular coloboma is characterized by defined punched out atrophic lesions of the macula. The present study aimed to investigate the genetic alterations of one Chinese sporadic patient with bilateral large macular coloboma. Complete ophthalmic examinations, including best‑corrected visual acuity, slit‑lamp examination, fundus examination, fundus photograph and fundus fluorescein angiography imaging, Pentacam, and optical coherence tomography were performed on the patient. Genomic DNA was extracted from leukocytes in a peripheral blood sample collected from the patient, the patient's unaffected family members and from 200 unrelated control subjects from the same population. Next‑generation sequencing of the known genes involved in ocular disease was performed. The functional effects of the mutation were analyzed using Polymorphism Phenotyping (PolyPhen) and Sorting Intolerant From Tolerant (SIFT). One heterozygous bestrophin 1 (BEST1) mutation c.1037C>A (p.Pro346His, p.P346H) in exon 9 and one heterozygous regulating synaptic membrane exocytosis 1 (RIMS1) mutation c.3481A>G (p.Arg1161Gly, p.R1161G) in exon 23 were identified in the patient being investigated, but not in the unaffected family members or unrelated control subjects. Polyphen and SIFT predicted that the amino acid substitution p.P346H in the BEST1 protein is damaging. In addition, Polyphen predicted that the amino acid substitution p.R1161G in the RIM1 protein is damaging. The results of the current study have increased the mutation spectrums of BEST1 and RIMS1, and are valuable for improving the current genetic counseling process and developing novel therapeutic interventions for patients with macular coloboma.