Knobloch syndrome 3 is a rare hereditary disorder of the eyes first described in 2007. Knobloch syndromes 1 and 2 have some of the same features but are distinct conditions since they result from mutations on different chromosomes.
A four-generation consanguineous family from Pakistan has been reported. Infants are born with a reddish, hairless patch on the back of the head but there is no skull defect. Nightblindness leads to symptoms between 2 and 4 years of age. Progressive loss of vision proceeds from there to near or complete blindness by late teenage years.
The retina (which receives light and sends it to the brain) is degenerated and dysfunctional with abnormal pigmentation and loss of responses to light. The optic nerve that connects the eye to the brain shows evidence of degeneration as well. The lens of the eye is often cataractous and may be dislocated from its normal position. Retinal detachments have not been seen unlike that of patients with other forms of Knobloch syndrome.
Intelligence and development are normal.
This seems to be an autosomal recessive condition based on the large pedigree reported. No specific gene mutation has been found but a location on chromosome 17 has been identified which seems to contain a mutation. Parents are carriers for one of the presumed mutations while affected children seem to have inherited both changed copies. The risks of inheriting this condition are 1 in 4 for each child of carrier parents.
Ophthalmologists would make this diagnosis but a general examination by a pediatrician or family practitioner is recommended to rule out other abnormalities which are often present in other variants of Knobloch syndrome. Longevity seems to be normal.
Cataractous and/or dislocated lenses can be surgically removed. The scalp defect generally does not require treatment.