From OMIM
Lissencephaly ('smooth brain') results from migrational arrest of cortical neurons short of their normal destination, and can result in profoundly impaired intellectual development and seizures. In X-linked lissencephaly-1, affected males generally have more a severe phenotype compared to females. DCX mutations cause classic lissencephaly with impaired intellectual development in hemizygous males and a milder phenotype known as subcortical band heterotopia in females, sometimes in the same family. The subcortical lamina heterotopia found in heterozygous females is also referred to as 'double cortex' (DC) syndrome (des Portes et al., 1997). For a general phenotypic description and a discussion of genetic heterogeneity of lissencephaly, see LIS1 (607432). There are several X-linked loci that affect neuronal migration, including the Aicardi locus (304050).  http://www.omim.org/entry/300067

From MedlinePlus Genetics
Infants with ILS may have poor muscle tone (hypotonia) and difficulty feeding, which leads to poor growth overall. Hypotonia also affects the muscles used for breathing, which often causes breathing problems that can lead to a life-threatening bacterial lung infection known as aspiration pneumonia. Children with ILS often develop muscle stiffness (spasticity) in their arms and legs and an abnormal side-to-side curvature of the spine (scoliosis). Rarely, the muscle stiffness will progress to paralysis (spastic paraplegia). Individuals with ILS cannot walk and rarely crawl. Most children with ILS do not develop communication skills.

More than 90 percent of individuals with ILS develop epilepsy, often within the first year of life. Up to 80 percent of infants with ILS have a type of seizure called infantile spasms, these seizures can be severe enough to cause brain dysfunction (epileptic encephalopathy). After the first months of life, most children with ILS develop a variety of seizure types, including persisting infantile spasms, short periods of loss of consciousness (absence seizures); sudden episodes of weak muscle tone (drop attacks); rapid, uncontrolled muscle jerks (myoclonic seizures); and episodes of muscle rigidity, convulsions, and loss of consciousness (tonic-clonic seizures).

Isolated lissencephaly sequence (ILS) is a condition that affects brain development before birth. Normally, the cells that make up the exterior of the brain (cerebral cortex) are well-organized, multi-layered, and arranged into many folds and grooves (gyri). In people with ILS, the cells of the cerebral cortex are disorganized, and the brain surface is abnormally smooth with an absence (agyria) or reduction (pachygyria) of folds and grooves. In most cases, these abnormalities impair brain growth, causing the brain to be smaller than normal (microcephaly). This underdevelopment of the brain causes severe intellectual disability, delayed development, and recurrent seizures (epilepsy) in individuals with ILS.  https://medlineplus.gov/genetics/condition/isolated-lissencephaly-sequence