Knobloch syndrome - a rare collagenopathy, revealing peripheral avascular retina

Abstract

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.

Keywords: Knobloch syndrome; collagenopathy; high myopia; retinal detachment.