Knobloch syndrome

Knobloch syndrome (also known as Knobloch-Layer syndrome) is a rare autosomal recessive disorder characterized by the combination of high myopia with vitreoretinal degeneration leading to retinal detachment, and occipital skull defects ranging from occipital encephalocele to occipital cutis aplasia. The condition primarily affects the eyes and the central nervous system. The hallmark ocular features include severe myopia present from birth or early infancy, vitreoretinal degeneration, retinal detachment (often bilateral), lens subluxation, and cataracts, which can lead to significant visual impairment or blindness. The occipital defect is variable in severity and may present as a frank encephalocele (protrusion of brain tissue through a skull defect) or as a more subtle finding such as occipital scalp defect (cutis aplasia). Knobloch syndrome is caused by pathogenic variants in the COL18A1 gene, which encodes the alpha-1 chain of type XVIII collagen, a component of basement membranes. This protein plays an important role in the structural integrity of the eye and in the closure of the neural tube during embryonic development. The proteolytic fragment of collagen XVIII, known as endostatin, is involved in angiogenesis regulation and may contribute to the pathophysiology of the disease. Additional clinical features that have been reported in some patients include macular abnormalities, persistent fetal vasculature, epilepsy, and developmental delay, though cognitive function is often normal. There is currently no cure or disease-specific treatment for Knobloch syndrome. Management is supportive and multidisciplinary, involving ophthalmologists for monitoring and surgical treatment of retinal detachments and cataracts, neurosurgeons for management of encephalocele when present, and neurologists if seizures occur. Early detection and intervention for retinal detachment are critical to preserving vision. Genetic counseling is recommended for affected families. Regular ophthalmologic surveillance is essential given the high risk of progressive retinal complications.

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