Knobloch Syndrome 2
Patient Information
Characteristics
Background and History
Knobloch syndrome 2 is a rare hereditary disorder of the brain and eyes first described in 2011.
Clinical Correlations
Only one patient with this syndrome, an 18 month old female infant, has been identified. The clinical features are similar to those of Knobloch Syndrome 1 to some extent with the skull defect, called an occipital encephalocele, near-sightedness, cataract, and retinal degeneration. This patient had poor vision which deteriorated during some years of follow-up and she developed a detachment of the retina. Her lenses also were displaced. Brain imaging did not reveal any abnormalities. The only additional findings were some delay fine motor movements.
Genetics
Inheritance
This is an autosomal recessive condition that requires the presence of changes (mutations) in both copies of a specific gene. The parents of an affected individual which carry a single changed copy are clinically normal but confer a risk of 25% for Knobloch syndrome to each offspring.
Pedigree
Autosomal recessive
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
In order for autosomal recessive disorders to be expressed, offspring generally must inherit two mutations, one from each carrier parent. Carriers with only one mutation, such as the parents, do not have clinical disease. Note that carrier parents can expect that 1 in 4 children (25%) will inherit both mutations and have the disorder, 2 in 4 children (50%) will be carriers like their parents, while 1 in 4 children (25%) inherit neither mutation.
Diagnosis and Prognosis
The skull defect is usually visible at birth but sometimes can be subtle if only the overlying skin is involved. An ophthalmologist is needed to diagnose the ocular changes in this syndrome. While most retinal detachments can be repaired, such surgery is often unsuccessful in Knobloch syndrome.
The skull defect can be surgically closed and the cataracts/dislocated lenses can be removed.
Web Resources
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