Usher syndrome (USH) is an autosomal recessive hereditary disease, characterized as retinitis pigmentosa and deafness. According to the severity of hearing loss, presence or absence of vestibular dysfunction, Usher syndrome is divided into 3 clinical subtypes: USH1, USH2 and USH3. Due to the genetically heterogeneous, it is important and valuable to find out the gene mutations in USH patients, which will be helpful to prenatal diagnosis, early intervention and gene therapy. Till now, the following 13 USH-related chromosomal loci were reported in the literature: USH1B, USH1C, USH1D (CDH23 gene), USH1F (PCDH15 gene), USH1G (SANS gene), USH1E, USH1H, USH1J and USH1K, USH2A, USH2C, USH2D and USH3 (CLRN1 gene). Ten out of all 13 loci have been located and identified. But more mechanisms should be further investigated, such as the relationship between the locus of gene mutations and clinical symptoms, how the modified protein structures and functions trigger clinical symptoms.
ObjectiveTo identify the pathogenic genes and mutations in a family with Usher syndrome type 2.MethodsA three-generation family including 7 individuals was enrolled in this study. There were 2 male patients and 5 unaffected individuals. All participants was underwent related ophthalmologic examination, including best corrected visual acuity, slit-lamp, indirect ophthalmoscopy, electroretinogram (ERG), optical coherence tomography and visual field test. DNA was extracted from 3 ml peripheral venous blood of all participants. A total of 136 hereditary retinal disease target genes were screened and the DNA sequence was performed by Next-generation sequence analysis. Then the suspected mutations compared with databases to identify the suspected mutations, which should be verified with non-affected family members and 100 normal subjects by PCR and Sanger sequence.ResultsThe sequence result showed that 2 patients, the proband and his brother, carried complex heterozygous mutations in the USH2A gene: c.5459T＞C (p.M1820T) in exon 27, c.802G＞A (p.G268R) in exon 5 and c.1190T＞A (p.I397K) in exon 7. The c.5459T＞C and c.1190T＞A mutations in USH2A have not been reported in the literature and database. Although their mother carried c.5459T＞C (p.M1820T) and c.802G＞A (p.G268R), and their father carried c.1190T＞A (p.I397K) heterozygous mutations, the parents did not present phenotype. These mutations were not detected in other normal family members. The result was supported by co-segregation analysis.ConclusionThe heterozygous mutations c.5459T＞C (p.M1820T), c.1190T＞A (p.I397K) and c.802G＞A (p.G268R) in USH2A gene cause Usher syndrome in this family.
ObjectiveTo observe the gene mutations and clinical phenotypes in patients with Usher syndrome type 2 (USH2) and retinitis pigmentosa (RP).Methods From August 2018 to January 2019, 4 patients and 11 normal family members from 3 families of USH2 and RP who visited Henan Eye Hospital were enrolled in the study. Detailed medical history was obtained and visual acuity, fundus color photography, OCT, visual field, full field ERG examination were performed. Among the three families, pedigree 1 was diagnosed with USH2, pedigree 2 and pedigree 3 were diagnosed with RP. The peripheral venous blood of patients and their family members were collected, and the whole genomic DNA was extracted. Targeted capture next generation sequencing analysis was performed on these members, and Sanger sequencing and family co-segregation were verified.ResultsIn the family F1, the proband had symptoms of RP and sensorineural deafness. Sequencing revealed two heterozygous frameshift variants: c.13877-13880 del AGAC (p. Q4626P) in exon 64 and c.798 del T (p. F266L) in exon 5 of USH2A. Both patients of family 2 and 3 showed RP signs without deafness. Two heterozygous variants c.15178T＞C (p. S5060 P) in exon 70 and c.6986C＞A (p. P2329H) in exon 37, and a pathogenic heterozygous variant c.5836C＞T (p. R1946X) in exon 29 of USH2A were identified in family F2. A heterozygous missense variant c.14951C＞T (p. P4984L) in exon 68 and a variant c.11156G＞A (p. R3719H) in exon 57 of USH2A were found in family F3. The results of conservation analysis showed that the corresponding amino acid sites of USH2A p.Q4626P, p.F266L, p.S5060P, p.P2329H and p.P4984L were highly conserved in many species. Among these 7 pathogenic variants detected, M1-M4 and M6 were novel.ConclusionsMutation USH2A gene are the main cause of USH2 and non-syndromic RP. Different variants affect protein translation and synthesis, consequently causing different clinical phenotypes.
Usher syndrome (USH) is the most common cause of deaf-blindness diseases characterized by sensorineural hearing loss and retinitis pigmentosa. Patients are clinically and genetically heterogeneous, however, there are no convincing methods for prevention and treatment. USH2A is the most common disease-causing gene among 14 genes related to Usher syndrome. Great progress has been achieved in the pathogenic mechanism, animal models studies, diagnosis, and treatments based on gene therapy, cells transplantation and antisense oligonucleotide-based splice correction. Mutations in USH2A result in defects in USH complex proteins which involved in the transport function of the peripheral cilia region. There is respective limitations in established mouse and zebrafish animal models. Two promising treatments of this disease are introduced. One is clinical transplantation of visual organs which induced from corrected patient-derived induced pluripotent stem cells by the CRISPR/Cas9 system and another one is the RNA splicing therapy based on antisense oligonucleotides.
Cilia are hair-like protuberance on cells of the human body that play a vital role in organs generation and maintenance. Abnormalities of ciliary structure and function affect almost every system of the body, such as the brain, eyes, liver, kidney, bone, reproductive system and so on. Retinal photoreceptor cells are one of sensory neurons which convert light stimuli into neurological responses. This process, called phototransduction, takes place in the outer segments (OS) of rod and cone photoreceptors. OS are specialized sensory cilia, and disruptions in cilia genes, which are causative in a growing number of non-syndromic retinal dystrophies, such as retinitis pigmentosa, Leber’s congenital amaurosis. These syndromes are genetically heterogeneous, involving mutations in a large number of genes. They show considerable clinical and genetic overlap. At present, there are few researches on retinal ciliopathies and clinical treatment strategy. This review shows a comprehensive overview of ciliary dysfunction and visual development related diseases, which contributes to understand the characteristics of these diseases and take early intervention in clinic.
ObjectiveTo identify the causative gene in a family affected with Usher syndrome (USH) with retinitis pigmentosa sine pigmento (RPSP) and to analyze the genotype-phenotype correlation.MethodsA retrospective clinical study. A 9-year-old girl with RPSP type 1F USH diagnosed in the ophthalmology clinic of Henan Provincial People's Hospital in November 2019 and her parents were included in the study. The patient had bilateral night blindness for more than 4 years, she suffered from hearing loss 7 years, and is currently binaural sensorineural deafness. The best corrected visual acuity in both eyes was 0.5+. There was showed no obvious pigmentation on the fundus. The visual acuity of the peripheral field of vision decreased. Optical coherence tomography showed that the outer layer of the peripheral retina became thinner and the ellipsoid band disappeared. On electroretinogram examination, the rod and cone system response was severely decreased. The clinical phenotype of the parents of the child were normal. The peripheral venous blood of the child and his parents were extracted, the whole genome DNA was extracted, the custom developed targeted capture kit (PS400) was used, and the next-generation sequencing technology was used to detect genetic mutations. The suspected pathogenic mutation sites were verified by Sanger; co-segregation was performed among family members. The pathogenicity of variants were evaluated according to the interpretation standards and guidelines of sequence variants. Bioinformatics techniques were used to assess the impact of variants on encoded proteins.ResultsThe results of genetic testing showed that the proband detected the PCDH15 gene c.4109dupA (p.K1370fs) (M1), c.17dupA (p.Y6_L7delinsX) (M2) compound heterozygous mutation sites, verified by Sanger sequencing, the mutations were in the family in a state of co-segregation. According to the evaluation of sequence variation interpretation standards and guidelines, M1 and M2 were pathogenic variants of the PCDH15 gene. M1 led to a complete change in the transmembrane structure of the encoded protein, and M2 caused the gene to only translate 6 amino acids, which predicted that the PCDH15 protein cannot be synthesized. According to the clinical phenotype, gene mutation pathogenicity and protein structure prediction, the final clinical diagnosis was PCDH15-related type 1F.ConclusionsPCDH15 genes c.4109dupA and c.17dupA are the pathogenic mutation sites of USH in this family. These compound heterozygous new mutations lead to the failure of normal synthesis of PCDH15 protein, which leads to ocular and ear manifestations.