Knobloch syndrome associated with Polymicrogyria and early onset of retinal detachment: two case reports

Surgical Outcomes of Retinal Detachment in Knobloch Syndrome

PURPOSE

To describe the rate, characteristics, and outcomes of rhegmatogenous retinal detachment (RD) in patients with Knobloch syndrome.

DESIGN

A single-center retrospective cohort study.

PARTICIPANTS

Fifty patients with Knobloch syndrome diagnosed clinically, with or without molecular confirmation of recessive pathogenic COL18A1 variants.

METHODS

A retrospective chart review of all patients diagnosed with Knobloch syndrome from November 1, 1983 to March 31, 2023. Demographic data, ophthalmic evaluation at baseline and follow-up, interventions, and final anatomic and visual outcomes were collected.

MAIN OUTCOME MEASURES

Rate, time of onset, characteristics, and treatment outcomes of RD.

RESULTS

Fifty patients with Knobloch syndrome were included. Males constituted 56% of cases. The diagnosis was confirmed with molecular genetic testing in 37 (74%) patients. Twenty-two patients (44%) had documented occipital bony defects or scalp lesions. Forty-eight of 100 eyes (48%) developed RD at a mean (standard deviation [SD]) age of 6.5 (6.1) years. The mean (SD) follow-up was 7.7 (5.6) years (range, 6 months to 24.3 years). Macular hole-related RD comprised 33% of RD cases. The overall single-surgery success rate was 36% and the final anatomic success rate was 70%. Macular hole-related RD carried a slightly worse prognosis with a 58% final anatomic success rate. Vitrectomy with adjunct scleral buckle and silicone oil tamponade provided the highest single-surgery success (62.2%). In eyes with measurable best-corrected visual acuity (BCVA), the mean preoperative BCVA was 1.2 logarithm of the minimum angle of resolution (Snellen equivalent, 20/320). After successful repair, mean visual acuity was 1.3 logarithm of the minimum angle of resolution (Snellen equivalent, 20/500).

CONCLUSIONS

Retinal detachment in Knobloch syndrome is frequent and occurs in young children. Macular hole-related RD comprises one third of RD cases and requires careful macular evaluation. Vitrectomy, combined with scleral buckling and silicone oil tamponade, appears to provide the best anatomic outcomes.

FINANCIAL DISCLOSURES

The authors have no proprietary or commercial interest in any materials discussed in this article.

Knobloch syndrome - a rare collagenopathy, revealing peripheral avascular retina

INTRODUCTION

Pediatric rhegmatogenous retinal detachments, especially those presenting at birth or soon afterward, have a high likelihood of syndromic associations that can be confirmed by genetic testing.

MATERIALS AND METHODS

A 5-month-old child was found to have high myopia in the right eye (RE) with highly tessellated fundus, opalescent vitreous, and peripheral thinning. Left eye had a shallow retinal detachment for which he underwent belt buckling. The baby had an occipital skin tag. A provisional diagnosis of Stickler syndrome was made.

RESULTS

On 1-month follow-up, left eye retina was attached and 360° laser barrage was done. Fluorescein angiography was done which revealed peripheral avascular retina in both eyes. MRI and genetic testing were suggestive of syndromic association. Genetic testing revealed pathogenic mutation in COL 18A1 suggestive of Knobloch syndrome in the baby, and both parents were found to be carriers of the same mutation. However, brain MRI showed features not pathognomonic of Knobloch syndrome.

CONCLUSION

Although Knobloch syndrome is associated with vitreoretinal degeneration and high risk of retinal detachment, there seems to be no recommendation for prophylaxis in the other eye and therefore we preferred to observe the RE closely. A unique feature noted in our case was the peripheral avascular zone (PAZ). The PAZ could be contributed by multiple factors such as high myopia, or due to endostatin deficiency (which is a derivative of collagen XVIII) or an underlying WNT signalling abnormality.

The genetics and disease mechanisms of rhegmatogenous retinal detachment

Rhegmatogenous retinal detachment (RRD) is a sight threatening condition that warrants immediate surgical intervention. To date, 29 genes have been associated with monogenic disorders involving RRD. In addition, RRD can occur as a multifactorial disease through a combined effect of multiple genetic variants and non-genetic risk factors. In this review, we provide a comprehensive overview of the spectrum of hereditary disorders involving RRD. We discuss genotype-phenotype correlations of these monogenic disorders, and describe genetic variants associated with RRD through multifactorial inheritance. Furthermore, we evaluate our current understanding of the molecular disease mechanisms of RRD-associated genetic variants on collagen proteins, proteoglycan versican, and the TGF-β pathway. Finally, we review the role of genetics in patient management and prevention of RRD. We provide recommendations for genetic testing and prophylaxis of at-risk patients, and hypothesize on novel therapeutic approaches beyond surgical intervention.

Mutations in the COL18A1 gen associated with knobloch syndrome and structural brain anomalies: a novel case report and literature review of neuroimaging findings

. 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.

Whole genome sequencing in a Knobloch syndrome family confirms the molecular diagnosis

BACKGROUND

To establish the molecular diagnosis in two brothers presenting with the ocular features of Knobloch Syndrome using whole genome sequencing (WGS).

METHODS

Clinical examination and ophthalmological phenotyping were completed under general anaesthesia. DNA samples were tested on a targeted retinal dystrophy next-generation sequencing panel. Subsequently, WGS was performed to identify additional variants.

RESULTS

Clinical examination confirmed the diagnosis of Knobloch Syndrome. Targeted sequencing identified a novel heterozygous frameshift pathogenic variant in COL18A1, c.2864dupC; p.(Gly956ArgfsX20), inherited from their mother. A second paternally inherited heterozygous missense variant was identified in both brothers, c.5014 G > A; p.(Asp1672Asn), which was initially considered to have too high frequency to be pathogenic (MAF 8.8%). This led to an in-depth analysis of the COL18A1 locus using WGS data, which confirmed that Asp1672Asn is a likely pathogenic hypomorphic allele.

CONCLUSION

To date, all confirmed genetic diagnoses of Knobloch syndrome are attributable to variants in COL18A1. The family described here has a heterozygous novel loss of function variant. Detailed analysis of WGS data combined with family segregation studies concluded that although Asp1672Asn has a high population frequency, it is the most likely second pathogenic variant in our family. This supports the hypothesis that this is a hypomorphic allele, which, in combination with a loss of function pathogenic variant, leads to Knobloch syndrome.To our knowledge, this is the first time that WGS has been used to confirm a molecular diagnosis of Knobloch syndrome in this way and has provided further insight into the molecular mechanisms in this rare disorder.

Knobloch Syndrome Associated with Novel COL18A1 Variants in Chinese Population

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.

Excitatory/Inhibitory Synaptic Ratios in Polymicrogyria and Down Syndrome Help Explain Epileptogenesis in Malformations

BACKGROUND

The ratio between excitatory (glutamatergic) and inhibitory (GABAergic) inputs into maturing individual cortical neurons influences their epileptic potential. Structural factors during development that alter synaptic inputs can be demonstrated neuropathologically. Increased mitochondrial activity identifies neurons with excessive discharge rates.

METHODS

This study focuses on the neuropathological examinaion of surgical resections for epilepsy and at autopsy, in fetuses, infants, and children, using immunocytochemical markers, and electron microscopy in selected cases. Polymicrogyria and Down syndrome are highlighted.

RESULTS

Factors influencing afferent synaptic ratios include the following: (1) synaptic short-circuitry in fused molecular zones of adjacent gyri (polymicrogyria); (2) impaired development of dendritic spines decreasing excitation (Down syndrome); (3) extracellular keratan sulfate proteoglycan binding to somatic membranes but not dendritic spines may be focally diminished (cerebral atrophy, schizencephaly, lissencephaly, polymicrogyria) or augmented, ensheathing individual axons (holoprosencephaly), or acting as a barrier to axonal passage in the U-fiber layer. If keratan is diminished, glutamate receptors on the neuronal soma enable ectopic axosomatic excitatory synapses to form; (4) dysplastic, megalocytic neurons and balloon cells in mammalian target of rapamycin disorders; (5) satellitosis of glial cells displacing axosomatic synapses; (6) peri-neuronal inflammation (tuberous sclerosis) and heat-shock proteins.

CONCLUSIONS

Synaptic ratio of excitatory/inhibitory afferents is a major fundamental basis of epileptogenesis at the neuronal level. Neuropathology can demonstrate subcellular changes that help explain either epilepsy or lack of seizures in immature brains. Synaptic ratios in malformations influence postnatal epileptogenesis. Single neurons can be hypermetabolic and potentially epileptogenic.

Knobloch Syndrome in Siblings with Posterior Fossa Malformations Along with Cerebellar Midline Cleft Abnormality Caused by Biallelic COL18A1 Mutation: Case-Based Review

Knobloch syndrome (KS) is an autosomal recessive disorder caused by biallelic pathogenic variants in COL18A1 . KS clinically manifests with the typical eye findings (high myopia, vitreoretinal degeneration, retinal detachment, and lens subluxation), variable neurological findings (occipital encephalocele, polymicrogyria, cerebellar malformations, epilepsy, and intellectual disability), and the other uncommon clinical manifestations. Literature review of all KS patients (source PubMed) was done with special reference to cerebellar abnormalities. Here, we report two siblings with typical KS with posterior fossa malformations and novel cerebellar midline cleft abnormality analyzed by whole exome sequencing. Known pathogenic homozygous variant c.2908C > T; (p.Arg970Ter) in exon 26 of COL18A1 was found as a cause for KS. These two siblings presented with early-onset severe ocular manifestations, facial dysmorphism, and variable central nervous system manifestations along with novel cerebellar midline cleft abnormality. The presence or absence of structural brain malformations and genotypes does not absolutely predict cognitive functions in KS patients. However, the presence of posterior fossa abnormality may be predictive for the development of ataxia in later life and needs further studies.

Macular Hole-Related Retinal Detachment in Children with Knobloch Syndrome

PURPOSE

To describe the findings and the management of macular hole (MH)-related retinal detachment (RD) in children with Knobloch syndrome.

DESIGN

Retrospective interventional case series.

PARTICIPANTS

Patients with Knobloch syndrome who presented with MH-related RD.

METHODS

Retrospective chart review of patients with Knobloch syndrome who presented with MH-related RD from January 2012 to December 2018. Interventions included pars plana vitrectomy and silicone oil tamponade with or without scleral buckle, drainage retinotomy, or relaxing retinectomy.

MAIN OUTCOME MEASURES

MH characteristics and surgical anatomical outcome.

RESULTS

The study included 9 eyes of 5 patients (age range 2 months to 5 years; median age 5.5 months). Presenting symptoms were poor fixation and nystagmus. The fellow eye of 1 patient had RD due to peripheral breaks. The MH was clinically visible in 8 eyes and detected only by OCT in 1 eye. The RD was shallow and extended to the anterior equator in 7 eyes and localized to a punched-out atrophic lesion in 1 eye. Seven eyes underwent surgical repair. At the last follow-up examination (follow-up range 11 to 42 months; mean 24 months, standard deviation 11.8 months), retinal reattachment with MH closure was achieved in 5 eyes along with marked improvement in fixation.

CONCLUSION

Patients with Knobloch syndrome may develop MH-related RD as early as infancy. The condition may be easily overlooked in children but should be suspected in the setting of high myopia, vitreoretinal degeneration, and encephalocele.