COL18A1 encodes the α1 chain of collagen type XVIII, a nonfibrillar collagen expressed in vascular and epithelial basement membranes. Biallelic pathogenic variants in COL18A1 have been associated with Knobloch syndrome, a condition defined by ophthalmologic abnormalities, though patients often have some or all of brain malformations, epilepsy, and intellectual disability. We reviewed our research and clinical databases for patients with seizures and biallelic COL18A1 variants suspected to be pathogenic. Three patients were identified, all of whom had epilepsy and global development impairment, with two having had developmental regression and drug-resistant seizures. None of the patients had severe ophthalmologic disease. All three patients had one heterozygous likely pathogenic frameshift COL18A1 variant on one allele, with the other allele carrying a rare heterozygous missense COL18A1 variant of less certain pathogenicity. These data raise the possibility that COL18A1 disruption could produce phenotypes without severe eye abnormalities but significant neurologic dysfunction.

We report a 39-year-old woman with lifelong visual impairment who presented in June 2024 with progressive visual deterioration in her right eye. Ophthalmologic evaluation revealed severe high myopia, vitreoretinal degeneration, phthisis bulbi of the left eye, and downward lens dislocation of the right eye. Neurological workup revealed bilaterally blurred optic discs, an elevated cerebrospinal fluid opening pressure of 31 cm H2O that normalized on repeat lumbar puncture, nonspecific white matter signal changes on MRI, and bilateral frontal polymicrogyria. Initial mild homocysteine elevation prompted consideration of homocystinuria; however, whole-exome sequencing identified a homozygous frameshift mutation in COL18A1 (c.2824_2831del, p.Gly942Argfs*142), confirming Knobloch syndrome type 1. This case illustrates an adult presentation of Knobloch syndrome with retinitis pigmentosa-like retinal changes and lens dislocation mimicking homocystinuria.

To explore the clinical phenotype and genetic characteristics in two children with Knobloch syndrome (KNO) due to variants of COL18A1 gene. Two children presented at the Genetic Eye Disease Clinic of the Eye Hospital of Wenzhou Medical University in October 2023 for ocular lesions were selected as the study subjects. Relevant clinical data and peripheral venous blood samples were collected from the children and their parents. Following genomic DNA extraction, whole-exome sequencing (WES) was carried out. Candidate variants were verified by Sanger sequencing of the family members. This study was approved by the Medical Ethics Committee of the hospital (Ethics No.: 2021-212-K-185). Both children exhibited characteristic ocular features of KNO including nystagmus, high myopia, and leopard spot fundus. Additionally, child 1 also presented with congenital occipital bone dysplasia and occipital encephalocele, while child 2 was diagnosed with vitreoretinochoroidopathy and bilateral high myopia. WES has identified compound heterozygous variants of the COL18A1 gene in both children, including a c.3013+3A>C splice-site variant and a c.2743C>T (p.Arg915Ter) nonsense variant in child 1, and a novel c.1702-1G>A splice-site variant and a c.3836C>T (p.Ser1279Leu) missense variant in child 2. A comprehensive literature review has identified 63 domestic and international articles involving 167 patients with KNO whom can be classified into three subtypes, with KNO type I being the most common and caused by pathogenic variants in the COL18A1 gene. Both probands in this study were children with KNO type I. Analysis of the genotype-phenotype correlations and population distribution characteristics revealed that the KNO patients exhibited significant clinical and genetic heterogeneity, along with a broad geographic distribution, with a relatively greater number of cases reported in Brazil and China. and a broad geographic distribution, with the highest numbers reported in Brazil and China. While no significant difference in genotype distribution was observed between Chinese and non-Chinese patients, phenotypic disparities were noted, with the non-Chinese cohort showing significantly higher rates of retinal detachment and developmental delay (P < 0.05), whereas Chinese patients exhibited a greater proportion of macular hypoplasia (P < 0.05). The main clinical manifestations of KNO include high myopia, vitreoretinal dystrophy, and occipital encephalocele. The novel c.1702-1G>A splice-site variant identified in the COL18A1 gene has expanded the mutational spectrum of KNO type I and provided valuable insights for genetic diagnosis, counseling, and clinical management of the disease.

Autosomal recessive types of both syndromic and non-syndromic inherited myopia are common in Saudi Arabia (SA) because many people marry their relatives. The prevalence of syndromic myopathies in SA, like Stickler syndrome (SS), Knobloch syndrome (KS), and Marfan syndrome (MFS), further complicates the disease spectrum. The causative genes linked to the Knobloch, Marfan, and Pierson syndromes are COL18A1, FBN1, and LAMB2, respectively. Additionally, we found recessive types of non-syndromic high myopia that have a high chance of causing retinal detachment, like those linked to LRPAP1 and LEPREL1. In these cases, regular evaluation and early intervention, including prophylactic laser photocoagulation and pars plana vitrectomy, may improve the outcome. Advancements in genetic testing for diagnosis and prevention accelerate detection, facilitate early interventions, and provide genetic counseling. The utilization of artificial intelligence (AI), machine learning (ML), and the advancement of gene therapy offer promising avenues for personalized care. We place a high value on using genetic knowledge to create a national screening program and patient registry aimed at understanding the national burden of myopia, knowing that we have a high rate of consanguinity, which reflects pathogenic homozygous alleles and founder mutations. This initiative will incorporate genetic counseling and leverage innovative technologies, which are crucial for disease management, early identification, and prevention in Saudi Arabia's healthcare system.