Associated Ophthalmic Findings with Lissencephaly
|Classification and external resources|
From the Greek “lissos” meaning smooth and “encephalus” meaning brain, Lissencephaly is a disorder of neuronal migration in the brain during embryologic development which either results in a lack of brain gyri (“agyri”), producing the characteristic smooth surface to the Lissencephalic brain; or it results in an overabundance of gyri (“pachygyri”), producing a cobblestone appearance. Although there have been reports of Lissencephaly being caused by either viral infection in the first trimester or a lack of fetal brain blood flow, Lissencephaly is predominately a genetic disorder. In general, Lissencephaly is frequently associated with a number of systemic manifestations such as microcephaly, seizures, unusual facies, limb deformities, failure to thrive, psychomotor retardation and infant death. Ophthalmic manifestations are often associated with Lissencephaly, being more severe and common in Type 2 (Cobblestone) Lissencephaly
Based on phenotypic appearance, Lissencephaly is usually divided into type 1 and type 2 with some entities not fitting into either category; however, as more genetic links are made, Lissencephaly is now being more appropriately classified by genetic cause.
Lissencephaly is a rare disease with few studies investigating the rates of ophthalmic manifestations, but one study from Nabi et al. did specifically investigate the ophthalmic findings of twenty patients with either type 1 or type 2 Lissencephaly. Ocular findings in type 2 Lissencephaly tend to be more common and severe than in type 1 Lissencephaly.
Type 1 (Classic) Lissencephaly:
This aptly named classic form of Lissencephaly, in which the majority of the brain is smooth, is the most common form of Lissencephaly, and is caused by neuronal under-migration in development. Type I Isolated Lissencephaly is characteristically associated with a mutation of the gene LIS1 which is the most well-described genetic cause, but several other mutations in other genes can produce this disease as well.
According to the study by Nabi et al. ophthalmic findings associated with Type 1 Lissencephaly include abnormal VEP responses, cortical blindness, optic nerve hypoplasia, macular hypoplasia, optic atrophy and eso or exotropia. Nabi et al. extrapolated that a higher incidence of strabismus in this population likely reflects the higher incidence of strabismus in developmentally delayed children.
Another disease entity associated with LIS1 mutation and another mutated gene critical for normal facial development, Miller-Dieker Syndrome is characterized by mental retardation, a characteristic facial dysmorphism consisting of a high forehead, bitemporal atrophy, anteverted nostrils, a long philtrum with an abnormal upper lip, and micrognathia. 
Type 2 (Cobblestone) Lissencephaly:
Type 2 is caused by neuronal over-migration in development. Although sulci are present in type 2, they are reduced in size, giving the brain a cobblestone appearance. Type 2 is mostly strongly associated with three similar congenital muscular dystrophies (CMD) which all tend to occur with ophthalmic manifestations. Characteristics of all three entities include type 2 Lissencephaly, congenital muscular dystrophy and eye abnormalities such as coloboma, iris hypoplasia, Peter’s anomaly, PFV/PHPV, retinal dysplasia/malformation, retinal non-attachment, optic nerve coloboma, and optic nerve hypoplasia.
Walker-Warburg Syndrome (WWS):
The most common of the three related muscular dystrophies. Associated systemic findings include cerebellar malformations and posterior encephaloceles, hydrocephalus and ventricular dilation, profound mental retardation, cleft lip and palate, small testes and cryptorchidism, imperforate anus.
In addition to being the most common of the three CMDs, WWS has a higher incidence of ophthalmic abnormalities. Dobyns and Truwit studied 40 patients with WWS and their reported ophthalmic findings include: Microphthalmia (94%), retinal dysplasia (43%), optic nerve hypoplasia (95%), coloboma (11%), glaucoma (50%), abnormal anterior chamber angle (58%), cataracts (57%), abnormal pupils (58%), PHPV (80%). Additional reported retinal findings include corneal opacities, retinal gliosis, failure of retinal development, and “leopard spot” peripheral retinopathy.
Fukuyama Congenital Muscular Dystrophy:
Usually seen in Japanese patients. Similar to WWS, but generally less severe phenotypically. Severe mental retardation, microcephaly, seizures, slowly progressive muscle wasting, weakness with increased CK and, sometimes, calf pseudohypertrophy. Progressive hydrocephalus is rare. No cephaloceles.
Eye findings are rarer than those seen in WWS but include optic pallor, cataracts and retinal mottling/vascular changes.
Muscle-Eye-Brain (MEB) Disease:
Usually seen in people of Finnish descent. Systemic phenotypic findings can vary greatly but include neonatal hypotonia, moderate to severe weakness, severe mental retardation, and seizures.
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