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.
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.