OMIM ID:
Conjunctivitis, Ligneous
Alternate Names
Defective Genes
Clinical Characteristics
Ocular Features
The most common clinical feature of this disorder is conjunctivitis often precipitated by an injury or infection of the conjunctiva with typical inflammatory features. A thick, ligneous (wood-like) pseudomembrane containing clotted fibrin subsequently forms that appears white, yellow-white, or finally red. These can be surgically removed but tend to recur, often on an accelerated timescale. This process is most pronounced on the upper tarsal conjunctiva but often involves the bulbar conjunctiva and the cornea as well. Corneal involvement (in nearly a third of cases) can lead to vascularization, scarring, keratomalacia, and perforation. The disease may be intermittent.
Systemic Features
While the conjunctiva is most commonly involved, other mucosal surfaces such as oral, laryngeal, tracheal, and vaginal mucosas may have similar disease often concomitantly with the ocular lesions. Ligneous gingivitis consists of nodular lesions with ulceration and peridodontal tissue destruction. The ear may also be involved in the disease. Life-threatening airway obstruction is a threat, especially in children during acute recurrences. Occlusive hydrocephalus requiring shunting occurs in a significant number of affected children.
Genetics
Inheritance
This autosomal recessive condition seems to result from homozygous mutations in the PLG gene (6q26) that codes for plasminogen. Tears contain plasminogen activators that convert plasminogen into the fibrinolytic enzyme plasmin which normally clears conjunctival and corneal fibrin deposits. The lack of normal plasminogen allows fibrin to accumulate on all mucosal surfaces.
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.