A family with Knobloch syndrome

Fetal pleural effusions can arise in various contexts with different prognosis. They have been reported in fetuses presenting with hereditary or acquired conditions. One particularly rare genetic disorder, known as Knobloch syndrome, seems to emerge as a potential new cause of fetal pleural effusions, associated with severe outcomes. Knobloch syndrome 1 can be caused by biallelic variants in COL18A1. It is primarily characterized by its ophthalmic features, including severe vitreoretinal degeneration with retinal detachment and macular abnormalities. Neurological defects such as encephalocele and developmental delay, along with skeletal and renal malformations, are also associated with the syndrome. The Knobloch syndrome 2 is caused by monoallelic variants in the kinase domain of PAK2. It is less described and seems to also be associated with cardiac and respiratory damage in addition to the Knobloch syndrome 1 phenotype. PAK2 is a ubiquitous protein with a major implication in regulation and remodeling of the cytoskeleton and numerous other cellular pathways. Knobloch-associated variants seem to cause a loss of the kinase function of the protein. Even if the ophthalmic defects are almost constant, PAK2-associated Knobloch syndrome has slightly different features from Knobloch syndrome 1 in which pulmonary and lymphatic damages are still unseen. In a prenatal trio exome sequencing, we identified a novel de novo PAK2 missense variant, NM_002577.4:c.836 A > C, p.(Gln279Pro), classified as likely pathogenic in a 24 weeks of gestation fetus whose only sign was severe bilateral pleural effusion. From a literature review of patients, we recognize this sign as an important antenatal indicator of Knobloch syndrome 2, as it was the first sign identifiable in 2 out of 5 patients. This adds new evidence for the implication of this gene in fetal pleural effusions, with potentially severe outcomes.

Surgical Outcomes of Retinal Detachment in Knobloch Syndrome

Macular Hole–Related Retinal Detachment in Children with Knobloch Syndrome

A 5-year-old girl came to the Tianjin Medical University Eye Hospital in May 2021 because of her poor eyesight after birth. The physical examination showed that she had high myopia, esotropia, horizontal tremor, and high myopia retinopathy of both eyes. After inquiring about her medical history, we found that the baby's occipital cystic mass swelled after birth, and CT examination showed that the occipital skull plate defect with meningocele, but without treatment, at present, the occipital mass had subsided by itself. Considering the eye manifestations and skull changes of the child, it may be conformed to Knobloch syndrome, after the detection of V4 by full exon gene, it was found that the child had the compound heterozygous variation of pathogenic gene COL18A1, and Knobloch syndrome was definite, Knobloch syndrome is a rare autosomal recessive hereditary disease with typical features of high myopia, retinal detachment and occipital encephalocele. At present, there is no clear treatment plan, and gene therapy may be an effective treatment for Knobloch syndrome in the future.

ABSTRACTPurpose: Knobloch syndrome is a pathognomonic vitreo-retinopathy that includes zonular weakness, high myopia, and a distinct fundus appearance with tessellation out of proportion to the degree of myopia. Whether myopia in Knobloch syndrome is axial or lenticular is unclear. Also not known are the optical coherence tomography (OCT) correlates to the distinct fundus appearance. In this study we assess cycloplegic refraction, biometry, and macular spectral domain (SD) OCT in children with Knobloch syndrome.Methods: A retrospective case series of seven children (12 eyes) with Knobloch syndrome.Results: Twelve eyes with attached retinas (seven patients, aged 6–17 years old, mean 11 years) were identified, seven of which had OCT. Best-corrected vision was typically 20/300 or worse. Axial length divided by corneal radius was >3 for all eyes (3.23–3.77, mean 3.52), consistent with axial myopia, and axial lengths (26.58–30.27 mm, mean 28.16) were consistent with spherical equivalent degree of myopia (−10.00 to −18.50, mean −12) when compared to historical controls. OCT revealed lack of choriocapillaries, outer retinal disorganization, and lack of or only rudimentary foveal pit.Conclusions: Refractions and biometry in Knobloch syndrome are consistent with the myopia being axial. In addition to vitreo-retinopathy, choroidopathy is part of the phenotype and is an anatomical correlate to the distinctive fundus appearance.

Knobloch syndrome is a rare, recessively inherited disorder classically characterized by high myopia, retinal detachment, and occipital encephalocele. Our aim is to report the clinical and genetic findings of four Israeli children affected by Knobloch syndrome. Retrospective study of four patients diagnosed with Knobloch syndrome, who underwent full ophthalmic examination, electroretinography, and neuroradiologic imaging. Genetic analysis included whole exome sequencing (WES) and Sanger sequencing. The four patients included in this study had high myopia and nystagmus at presentation. Ocular findings included vitreous syneresis, macular atrophy, macular coloboma, and retinal detachment. One child had iris transillumination defects and an albinotic fundus, initially leading to an erroneous clinical diagnosis of albinism. Electroretinography revealed a marked cone-rod pattern of dysfunction in all four children. Brain imaging demonstrated none to severe occipital pathology. Cutaneous scalp changes were present in three patients. WES analysis, confirmed by Sanger sequencing revealed COL18A1 biallelic null mutations in all affected individuals, consistent with autosomal recessive inheritance. This report describes variable features in patients with Knobloch syndrome, including marked lack of eye pigment similar to albinism in one child, macular coloboma in two children as well as advanced cone-rod dysfunction in all children. One patient had normal neuroradiologic findings, emphasizing that some affected individuals have isolated ocular disease. Awareness of this syndrome, with its variable phenotype may aid early diagnosis, monitoring for potential complications, and providing appropriate genetic counseling.

Knobloch syndrome is an autosomal recessive disorder associated with early-onset ocular abnormalities and central nervous system malformations. Ocular abnormalities are usually severe, and include high myopia, vitreoretinal degeneration, retinal detachment, macular abnormalities, and cataract. The most frequent systemic changes are midline malformations of the brain, ventricular dilation, and occipital encephalocele. Cognitive delay may occur. We report a case of cataract in a child with Knobloch syndrome. Cataract surgery and follow-up are described.

Background Knobloch syndrome results from recessive mutations in COL18A1 and is characterized by retinopathy and occipital scalp, brain and skull defects. Methods and Materials We report three siblings, born to consanguineous parents, two of whom with genetically confirmed Knobloch syndrome due to a homozygous pathogenic variant c.4054_4055del; p.Leu1352Valfs*72 in COL18A1. Results With the lack of classic occipital findings, an initial diagnosis of familial exudative vitreoretinopathy was entertained in these siblings because of the history of retinal detachments, retinal pigmentary changes and abnormal vitreous. The diagnosis of Knobloch syndrome was eventually made through molecular genetic testing using an extensive panel. In one patient presenting with acute retinal detachment and posteriorly dislocated intraocular lens implant, reattachment surgery was successful in stabilizing vision. Conclusion The clinical diagnosis of Knobloch syndrome can be difficult to reach in the absence of the typical occipital scalp defects. A careful medical history, detailed clinical examination and molecular genetic testing will reveal the correct diagnosis of Knobloch syndrome in atypical cases.

Biallelic variants of COL18A1 cause Knobloch syndrome (KNO), a rare genetic disorder, characterized by oculopathy and structural defects. Recently, several studies have suggested that novel de novo missense variants in PAK2 may be associated with KNO; however, there are few case reports. This study aimed to investigate a patient with KNO who initially presented with seizures and expand the PAK2 genotype and phenotype spectrum. This study included a Chinese family with a proband who primarily presented with epilepsy and developmental delay. Whole-exome sequencing and Sanger sequencing were performed to analyze potential variants. Structural modeling was performed to assess the impact of the variant on the protein structure. Invitro, a mutant plasmid was constructed and transfected into 293T cells to conduct phosphorylation assays, and phosphorylation levels at Ser141 of PAK2 were assessed. The PAK kinase inhibitor FRAX597 was used to confirm the specificity of the western blot results. A de novo variant of PAK2 gene, NM_002577.4: c.1049G>A (p.Arg350Lys) was found in the patient but not in his parents or sister. This variant was found to be located in the kinase domain and may alter the hydrogen-bond network, potentially affecting kinase activity. Invitro functional experiments demonstrated that the variant may lead to reduced protein levels. Moreover, Western blot analysis showed a significant decrease in the phosphorylation level at Ser141 compared to the wild-type plasmid, indicating that the variant may lead to decreased PAK2 phosphorylation levels. The clinical manifestations in this patient may be associated with a novel PAK2 variant, and the atypical presentation of KNO suggests that PAK2-related KNO may have a broader phenotypic spectrum.

Molecular Analysis of Collagen XVIII Reveals Novel Mutations, Presence of a Third Isoform, and Possible Genetic Heterogeneity in Knobloch Syndrome

We report cases of acute angle closure in two young highly myopic siblings with Knobloch syndrome. To our knowledge, this is the first report of acute angle closure in Knobloch syndrome. Both patients were homozygous for a likely pathogenic variant in COL18A1. Both responded to treatment with cyclophotocoagulation and remained stable despite declining or being medically unfit for clear lens extraction. We argue that the recent implication of heterozygous mutations in COL18A1 in familial angle closure supports the argument that acute angle closure in these two patients was likely to be a thus far unreported feature of Knobloch syndrome. In addition, these cases also support the hypothesis that pathogenic variants in COL18A1 may be a risk factor for acute angle closure.

Knobloch syndrome is an inherited disorder characterized by high myopia, retinal detachment, and occipital defects. Disease-causing mutations have been identified in the COL18A1 gene. This study aimed to investigate novel variants of COL18A1 in Knobloch syndrome and describe the associated phenotypes in Chinese patients. We reported six patients with Knobloch syndrome from four unrelated families in whom we identified five novel COL18A1 mutations. Clinical examination showed that all probands presented with high myopia, chorioretinal atrophy, and macular defects; one exhibited rhegmatogenous retinal detachment in one eye. Occipital defects were detected in one patient.

Knobloch syndrome is a rare, recessively inherited disorder classically characterized by high myopia, retinal detachment, and occipital encephalocele, but it is now known to have an increasingly variable phenotype. There is a lack of reported electrophysiologic data, and some key clinical features have yet to be described. To expand on current clinical, electrophysiologic, and molecular genetic findings in Knobloch syndrome. Twelve patients from 7 families underwent full ophthalmic examination and retinal imaging. Further investigations included electroretinography and neuroradiologic imaging. Bidirectional Sanger sequencing of COL18A1 was performed with segregation on available relatives. The study was conducted from July 4, 2013, to October 5, 2015. Data analysis was performed from May 20, 2014, to November 3, 2015. Results of ophthalmic and neuroradiologic assessment and sequence analysis of COL18A1. Of the 12 patients (6 males; mean age at last review, 16 years [range, 2-38 years]), all had high myopia in at least 1 eye and severely reduced vision. A sibling pair had unilateral high myopia in their right eyes and near emmetropia in their left eyes from infancy. Anterior segment abnormalities included absent iris crypts, iris transillumination, lens subluxation, and cataract. Two patients with iris transillumination had glaucoma. Fundus characteristics included abnormal collapsed vitreous, macular atrophy, and a tesselated fundus. Five patients had previous retinal detachment. Electroretinography revealed a cone-rod pattern of dysfunction in 8 patients, was severely reduced or undetectable in 2 patients, and demonstrated cone-rod dysfunction in 1 eye with undetectable responses in the other eye in 2 patients. Radiologic imaging demonstrated occipital encephalocele or meningocele in 3 patients, occipital skull defects in 4 patients, minor occipital changes in 2 patients, and no abnormalities in 2 patients. Cutaneous scalp changes were present in 5 patients. Systemic associations were identified in 8 patients, including learning difficulties, epilepsy, and congenital renal abnormalities. Biallelic mutations including 2 likely novel mutations in COL18A1, were identified in 6 families that were consistent with autosomal recessive inheritance with a single mutation identified in a family with 2 affected children. This report describes new features in patients with Knobloch syndrome, including pigment dispersion syndrome and glaucoma as well as cone-rod dysfunction on electroretinography. Two patients had normal neuroradiologic findings, emphasizing that some affected individuals have isolated ocular disease. Awareness of the ocular phenotype may aid early diagnosis, appropriate genetic counseling, and monitoring for potential complications.

Knobloch syndrome is a rare autosomal recessive disorder characterized by a triad of high myopia, vitreoretinal degeneration, and congenital occipital scalp defects. On literature review of all reported cases, 25 of 85 eyes (29%) of patients diagnosed as having Knobloch syndrome have suffered retinal detachment. Due to high myopia, surgical repair of the retinal detachment is challenging and patients frequently require several reoperations. Even after vitrectomy or scleral buckle for retinal detachment, the final visual acuity outcomes are poor, with 11 of 12 (92%) patients having 20/200 visual acuity or worse and 6 of 12 (50%) having counting fingers visual acuity or worse. The role of retinal detachment prophylaxis has been discussed for other vitreoretinal degeneration disorders, but not for this disease. The authors report the case of a child affected with Knobloch syndrome who presented with total retinal detachment in the left eye at 24 months of age. He underwent successful repair and was then treated with prophylactic scleral buckle implantation in the right eye 5 months later. The retina in both of his eyes remains attached 4 years later. [J Pediatr Ophthalmol Strabismus 2014;51:e40–e43.]

. COL18A1 gene mutations have been associated with Knobloch syndrome, which is characterized by ocular and brain abnormalities. Here we report a 4.5 years-old male child with autism and two novel COL18A1 mutations (NM_030582.4: c.1883_1891dup and c.1787C>T). Hypermetropic astigmatism, but not brain migration disorders, was observed. However, an asymmetric pattern of cerebellar perfusion and a smaller arcuate fascicle were found. Low levels of collagen XVIII were also observed in the patient´s serum. Thus, biallelic loss-of-function mutations in COL18A1 may be a new cause of autism without the brain malformations typically reported in patients with Knobloch syndrome.