Optical coherence tomography findings and successful repair of retina detachment in Knobloch syndrome

Severe retinal complications in Knobloch Syndrome - Three siblings without clinically apparent occipital defects and a review of the literature

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.

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.