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Isolated lissencephaly sequence
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Isolated Lissencephaly Sequence

Isolated lissencephaly sequence is a rare neurological condition characterized by an abnormally smooth brain surface, resulting in severe developmental delays and treatment-resistant epilepsy.

Overview & Symptoms

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. This underdevelopment of the brain causes severe intellectual disability, delayed development, and recurrent seizures (epilepsy) in individuals with ILS.

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 epilepsy, 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).

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. 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.

Frequency

ILS affects approximately 1 in 100,000 newborns.

Causes & Genetics

Mutations in the PAFAH1B1, DCX

Frequently Asked Questions

Most children need a feeding tube (gastrostomy) due to chronic dysphagia and poor weight gain. Respiratory muscle weakness can lead to recurrent infections and may require nighttime non‑invasive ventilation. Developmentally, severe intellectual disability is typical; early intervention with physical, occupational, and speech therapy, as well as special‑education services, can maximize functional abilities, but independence is limited. Palliative‑care involvement is often helpful for symptom management and family support.
First‑line therapy often includes hormonal treatment (ACTH) or vigabatrin for infantile spasms, followed by antiepileptic drugs such as topiramate, levetiracetam, or clobazam. Because seizures are frequently refractory, many children require a combination of medications, ketogenic diet, or referral for epilepsy surgery/neuromodulation. At home, keep a seizure diary, ensure a safe environment (padded corners, seizure‑alert monitoring), and have rescue medication (e.g., rectal diazepam) readily available per the neurologist’s plan.
Diagnosis relies on brain MRI, which shows a smooth or minimally folded cerebral cortex (agyria or pachygyria) and often a small brain volume. Genetic testing, usually a chromosomal microarray or targeted sequencing of known lissencephaly genes (e.g., LIS1, DCX, TUBA1A), confirms the molecular cause.
Look for severe developmental delay, poor muscle tone (hypotonia), difficulty feeding, and abnormal eye movements in the first months of life. The appearance of infantile spasms or other seizures before 12 months is a red flag that warrants urgent neurologic assessment.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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