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At a glance

An inherited disorder characterized by encephalocele, vitreoretinal degeneration with retinal detachment, high myopia, and normal intelligence. It is also characterized by cataracts, and the association with skull defects such as occipital encephalocele and occipital aplasia. Meningocele have also been reported as part of this medical disorder.

Synonyms

Vitreoretinal Degeneration with Retinal Detachment, Occipital Encephalocele Syndrome; Knobloch-Layer Syndrome; Retinal Detachment and Occipital Encephalocele Syndrome.

History

It is named after D. O. Knobloch who first described the syndrome in 1971.

Classification

There are three types of Knobloch Syndrome based on the underlying genetic expression (see Genetic inheritance).

Incidence

Approximately 35 patients have been reported in the literature.

Genetic inheritance

It is inherited as an autosomal recessive, caused by defective collagen XVIII. Gene map locus is 21q22.3. Penetrance seems to be 100%; however, variability (intra- and interfamilial) is considerable. Knobloch Syndrome Type 1 is caused by mutations in the COL18A1 gene. The genes involved in the expression of Knobloch Syndrome Type 2 and Type 3 have not been identified. However, Knobloch Syndrome Type 3 is believed linked to chromosome 17 (17q11.2). An autosomal recessive pattern of inheritance cannot be eliminated.

Pathophysiology

Condition controlled by a mutation in the COL18A1 collagen gene that is of variable expressivity. The cranial and eye alterations in this syndrome may occur early in embryogenesis, suggesting that developmental genes may be involved in the pathogenesis of this syndrome.

Diagnosis

Made based on the clinical findings. Histology may reveal heterotopic neuronal tissue in the skull lesions (thereby distinguishing between scalp defect and encephalocele).

Clinical aspects

The most common findings are high myopia, vitreoretinal degeneration with retinal detachment, and occipital encephalocele. Intelligence is usually normal. This led to the assumption, that in many cases the encephalocele may in fact be either a meningocele or a scalp defect. Heterotopic neuronal tissue could be found in the scalp lesions of some patients. Other reported, but inconstant findings include ☞Scimitar Syndrome, patent ductus arteriosus, single umbilical artery, mild congenital pulmonary lymphangiectasia (visible on chest radiographs as interstitial changes), and abnormal palmar creases.

Precautions before anesthesia

A complete history and thorough examination is required. Ask about pulmonary problems (respiratory distress, cyanosis, cough) and rule out encephalocele (important for positioning of the patient).

Anesthetic considerations

If an occipital encephalocele/meningocele is present, induction of anesthesia is best performed in the left lateral position or alternatively on bolsters avoiding any pressure on the lesion. Congenital pulmonary lymphangiectasia is often fatal in the neonatal period; respiratory distress has not been described in these patients, which probably indicates a ...

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