The distinct ophthalmic phenotype of Knobloch syndrome in children

Knobloch syndrome is defined as a triad of occipital defect, high myopia and vitreo-retinal degeneration (often with later retinal detachment); however, the ocular phenotype is not well defined. This report characterises eye findings of the syndrome in children with genetically confirmed disease.

Case series of Saudi children with previously documented homozygous mutations in COL18A1 or ADAMTS18.

All eight children (4-15 years old; five families) had smooth (cryptless) irides, high myopia (-10 to -20 dioptres) and distinctive vitreo-retinal degeneration consisting of diffuse very severe retinal pigment epithelium atrophic changes with prominent choroidal vessel show, macular atrophic lesions with or without a 'punched out' appearance and white fibrillar vitreous condensations. In two probands and a sibling, this distinctive retinal appearance was the basis for initial clinical diagnosis. Six children had temporal ectopia lentis and four had posterior perinuclear lens opacity. Additional features included developmental delay (two), epilepsy (one) and heterotopic grey matter in the lateral ventricles (one). Four children had no clinically discernible occipital defect.

Taken together, smooth iridies, ectopia lentis and characteristic vitreo-retinal degeneration seem pathognomonic. Although it is a defining feature of the syndrome, clinically discernible occipital defect is not a sine qua non for the diagnosis. Ophthalmologists are uniquely able to diagnose Knobloch syndrome.