The types of seizures associated with lissencephaly include:

persisting spasms
focal seizures
tonic seizures
atypical seizures
atonic seizures Other possible symptoms of lissencephaly include telecanthus, estropia, hypertelorism, varying levels of mental retardation, cerebellar hypoplasia, corpus callosum aplasia, and decreased muscle tone and tendon reflexes. Over 90% of children affected with lissencephaly have seizures.Patients with subcortical band heterotopia (another disorder associated with pachygyria) typically have milder symptoms and their cognitive function is closely linked to the thickness of the subcortical band and the degree of pachygyria present. Causes
Pachygyria is caused by a breakdown in the fetal neuronal migration process due to genetic or possibly environmental influences. The affected cerebral cortex will typically have only four developed layers instead of the normal six. One of the best known and most common types of neuronal migration disorders is lissencephaly, a diffuse cortical malformation relating directly to agyria and pachygyria. Incomplete neuronal migration during the early fetal brain development is the precursor to lissencephaly. Should neurons follow an abnormal migration during development possible cortical malformations include classical lissencephaly (as stated above) and subcortical band heterotopia with an agyria-pachygyria band spectrum.
The most common lissencephaly observed, consisting of frontotemporal pachygyria and posterior agyria, is Grade 3. Another malformation worth mentioning because of its connections to pachygyria is polymicrogyria. Polymicrogyria is characterized by many small gyri separated by shallow sulci, slightly thin cortex, neuronal heterotopia and enlarged ventricle and is often superimposed on pachygyria. Treatment
Because pachygyria is a structural defect no treatments are currently available other than symptomatic treatments, especially for associated seizures. Another common treatment is a gastrostomy (insertion of a feeding tube) to reduce possible poor nutrition and repeated aspiration pneumonia. Microcephalic osteodysplastic primordial dwarfism
Microcephalic osteodysplastic primordial dwarfism (MOPD) type II is an autosomal multisystem disorder including severe pre- and post-natal growth retardation, microcephaly with Seckel syndrome-like facial appearance, and distinctive skeletal alterations. Usually those affected have mild to moderate mental retardation. See also
Lissencephaly
Polymicrogyria

References
Phadke SR, Girisha KM, Phadke RV (2007). "A new autosomal recessive disorder of bilateral frontotemporal pachygyria without microcephaly: report of a case and review of literature". Neurol India. 55 (1): 57–60. doi:10.4103/0028-3886.30429. PMID 17272902. External links

Online Mendelian Inheritance in Man (OMIM): 600176