ObjectiveTo observe and analyze the pathogenic genes and clinical phenotype characteristics of retinitis pigmentosa sinepigmento(RPSP). MethodsA retrospective clinical study. Two patients (proband) and five family members from two RPSP families admitted to Xiamen Eye Center of Xiamen University in December 2022 and Shenzhen Eye Hospital in July 2023 were included in the study. Two families have no blood relationship and were both Han Chinese. Detailed ocular and systemic medical history and specialized examinations were performed for all members, including color fundus photography, fundus autofluorescence (FAF), and full field electroretinogram (ff-ERG) examination. The peripheral venous blood of all members was collected, and genomic DNA was extracted. Pathogenic genes and their loci were screened using whole exome high-throughput sequencing technology. Sanger sequencing was used to verify the pathogenic genes in the two pedigrees. The pathogenicity of candidate variants was evaluated according to the American Society for American College of Medical Genetics and Genomics (ACMG) classification criteria and guidelines for genetic variants. ResultsThe two probands were male, aged 9 and 7 years, respectively. The main complaint was poor binocular vision for 6 and 3 years and poor treatment effect of amblyopia. The proband (Ⅱ2) in family 1 had a pale red color on the optic disc, with leopard-like changes in the posterior pole and thinner retinal arteries. FAF showed mottled fluorescence attenuation outside the macular vascular arch. There was no significant waveform in both bright and dark visual responses of ff-ERG. He also had 6-toed deformity of both feet, renal cysts, and a slightly overweight body. The clinical diagnosis was non-pigmentary retinitis pigmentosa. The proband of family 2 (Ⅱ1) had poor binocular vision in a dark environment and had atrophy lesions on the nasal side of the optic disc and leopard print like changes in the fundus. FAF showed uneven enhancement in the fovea. ff-ERG showed severe abnormalities in dark and light response, with significant decrease and delay in b-wave amplitude and latency. He had no other systemic abnormalities. The clinical diagnosis was binocular RPSP. There were no abnormal ocular and systemic manifestations in the two family members. Gene sequencing revealed a homozygous mutation (c.534+1G>T) of BBS2 gene, which was inherited from the mother and father respectively. Based on clinical manifestations and genetic testing results, the final diagnosis was Bardet Biedl syndrome. The genetic sequencing results confirmed a novel compound heterozygous mutation (c.950T>G: p. Leu317Arg missense mutation and c.849+1G>C splicing mutation) of BBS7 gene. His father (Ⅰ1) and mother (Ⅰ2) carried M1 heterozygous variants. Combined with the clinical manifestations and genetic testing results, the final diagnosis was Bardet-Biedl syndrome (BBS). Family 2 proband (Ⅱ1) carried the BBS7 gene C.950T>G (p.Leu317Arg) (M2) missense variation and C.849 +1G>C (M3) splice site variation. His father (Ⅰ1) and mother (Ⅰ2) carried M3 shear site variation and M2 missense variation, respectively. The two families all fit the autosomal recessive inheritance pattern, and the genotype and clinical phenotype were coseparated. According to ACMG guidelines, M1, M2 and M3 were all identified as possible pathogenic variants. ConclusionsBBS2 gene M1 homozygous variation and BBS7 gene M2, M3 complex heterozygous variation are the possible pathogenic genes in family 1 and family 2, respectively. Two families are affected by BBS and RPSP, respectively.
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.