This study investigates a unique and complex eye phenotype characterized by minimal iris defects, foveal hypoplasia, optic nerve coloboma, and severe posterior segment damage. Through genetic analysis and bioinformatic tools, a specific nonsynonymous substitution, p.(Asn114Ser), within the PAX6 gene’s paired domain is identified. Although this substitution is not in direct contact with DNA, its predicted stabilizing effect on the protein structure challenges the traditional understanding of PAX6 mutations, suggesting a gain-of-function mechanism. Contrary to classical loss-of-function effects, this gain-of-function hypothesis aligns with research demonstrating PAX6’s dosage sensitivity. Gain-of-function mutations, though less common, can lead to diverse phenotypes distinct from aniridia. Our findings emphasize PAX6’s multifaceted influence on ocular phenotypes and the importance of genetic variations. We contribute a new perspective on PAX6 mutations by suggesting a potential gain-of-function mechanism and showcasing the complexities of ocular development. This study sheds light on the intricate interplay of the genetic alterations and regulatory mechanisms underlying complex eye phenotypes. Further research, validation, and collaboration are crucial to unravel the nuanced interactions shaping ocular health and development.

Background/Objectives: Knobloch syndrome 1 (KS) is an autosomal recessive inherited ocular syndrome characterized by a combination of high myopia, vitreoretinal degeneration, and occipital encephalocele. KS is caused by biallelic pathogenic variants in the COL18A1 gene. Diagnosing KS can be challenging due to its clinical heterogeneity and the rarity of the syndrome. Methods: We conducted comprehensive clinical and instrumental ophthalmological examinations, whole-exome sequencing, Sanger sequencing, and segregation analysis to evaluate affected families. Results: Two patients presenting with high myopia, low visual acuity, chorioretinal atrophy, and occipital skin/skull defects were diagnosed with Knobloch syndrome 1 (KS). In Case 1, a 14-year-old boy, the COL18A1 variants identified were c.2673dup and c.3523_3524del in a compound heterozygous state. Case 2 involved a 3-year-old girl, the c.1637_1638dup and c.3523_3524del variants were identified in a compound heterozygous state. In Case 3, a retrospectively observed boy of 3 y.o. with KS, the variants c.929-2A>G and c.3523_3524del were defined earlier. Conclusions: We confirmed KS molecularly in two novel families. Additionally, in Case 3 of a retrospectively analyzed third family and in both novel cases, one of the biallelic causative variants was the same known 2bp deletion in exon 40 of the collagen XVIII gene. Cases 1 and 3 were characterized by connective tissue dysplasia features and a pathognomonic Knobloch triad. No neurological manifestations and no trends in the genotype–phenotype relationship were found. The heterogeneity of phenotype in the case series is likely to be the result of further factors and/or genetic background.

To present the main aspects of interdisciplinary diagnostics of patients with hereditary retinal diseases and the first results of the follow-up of patients with inherited retinal dystrophies (IRD) caused by biallelic mutations in the gene RPE65 after gene replacement therapy in Russia. The cohort of patients consisted of six children (5-15 years old) with the diagnosis of Leber amaurosis type 2. All patients underwent a multi-disciplinary examination using conventional clinical, instrumental and molecular-genetic methods. Genetic diagnosis was established based on the results of two-stage DNA diagnostics using high-performance parallel sequencing of a custom panel and family segregation analysis by Sanger sequencing. In the Research Centre for Medical Genetics the first group of Russian patients with an orphan inherited retinal disease was verified, they underwent subretinal injection of the gene replacement drug Voretigene neparvovec (12 eyes) in the Helmholtz National Medical Research Center of Eye Diseases. According to the regulated terms of monitoring gene therapy patients, they were examined in the Research Centre for Medical Genetics after 1, 3, 6 and 12 months, and then once per year. Thus, the available data allows us to analyze the first results 3 months after the treatment. The presented data on inherited retinal dystrophies caused by biallelic mutations in the RPE65 gene emphasize the need to change the diagnostic algorithm in the ophthalmic practice. The use of clinical instrumental and molecular genetic diagnostic methods makes it possible to apply etiotropic treatment to patients with a disabling disease that was previously considered untreatable. The gene replacement drug Voretigene neparvovec registered in Russia showed irrefutable first positive results in all targeted patients.

The study purpose was to assess the diagnostic value of whole-genome sequencing (WGS) in identifying candidate genetic variants in patients with inherited retinal diseases (IRDs). We investigated 107 unrelated Russian patients with retinal diseases who carried single pathogenic variants in any of nine common autosomal recessive IRD genes (ABCA4, USH2A, EYS, CRB1, RPE65, CNGB3, CNGA3, CEP290, and GUCY2D). WGS was performed for all patients; candidate splice variants were functionally validated using minigene assays. The total diagnostic yield was 40.2% (43/107). In 25.2% of cases (27/107), the diagnosis was established by identifying a second variant in one of the following candidate genes: EYS (n = 9), USH2A (n = 8), ABCA4 (n = 5), CNGB3 (n = 3), CRB1 and CEP290 (n = 1 each). In 15.0% of cases (16/107), the diagnosis was reclassified by variants in alternative IRD genes (autosomal dominant, X-linked, mitochondrial, or syndromic). The majority of second variants detected in AR cases were CNVs (55.5%, 15 patients), followed by non-coding variants (26.0%, seven), structural rearrangements (14.8%, four) and exonic point variant (3.7%, one). Two recurrent CNVs were observed: a gross deletion of exons 22–24 in USH2A (n = 4) and a deletion partially affecting exon 19 of EYS (n = 4). Structural variants were mostly represented by delINV rearrangements (n = 5). Minigene assays confirmed that three novel deep intronic variants (in CHM, EYS, and CEP290) and one non-canonical splice-acceptor variant in USH2A which disrupt splicing, causes pseudoexon inclusion with premature termination or in-frame exon skipping respectively. Thus, WGS improves the diagnostic yield in IRDs by detecting variants missed by targeted sequencing, supporting its clinical utility in ophthalmologic practice.

Pathogenic heterozygous variants in the PIEZO2 gene cause distal arthrogryposis type 5 – a rare autosomal dominant disease, which is characterized by the development of congenital contractures, ophthalmoparesis, ptosis and restrictive respiratory disorders. We have presented clinical and genetic characteristics of seven Russian patients with distal arthrogryposis type 5 caused by previously described and newly identified nucleotide variants in the PIEZO2 gene. It was shown that the most severe clinical manifestations were found in patients with newly identified nucleotide variants c.8238GA (p.Trp274Ter) and c.7095GT (p.Trp2365Cys), while in patients with other previously described variants c.8181_8183delAGA (p.Glu2727del) and c.2134AG (p.Met712Val) the clinical phenotype is more moderately expressed. The dynamics of phenotype formation were also noted. It has been shown that the disease progression may occur as the child grows and requires monitoring of this group of patients.