What is lissencephaly? 

Lissencephaly describes a group of rare brain disorders, in which the brain surface appears smooth instead of wrinkled.¹

The surface of a healthy brain is covered in folds and grooves, called gyri and sulci, which are crucial for normal brain function. This is because they allow for an enormous number of brain cells to be packed in tightly, thereby enabling the brain to perform complex functions. Therefore, the absence of gyri and sulci can lead to severe developmental problems.²

The range of symptoms can vary, but most people with lissencephaly have delayed physical and cognitive development, muscle stiffness or floppiness, feeding difficulties, and seizures. In many cases, these challenges are lifelong and require continuous care.¹

Although the exact prevalence of lissencephaly is unknown, some research estimates that lissencephaly affects roughly 1 in 100,000 births.³

To better understand lissencephaly, it's helpful to first examine a crucial process, known as neuronal migration, in which brain cells move to their proper locations to form the brain’s basic structure.

Building the brain: The role of neuronal migration 

The brain's internal GPS system:

The human brain begins forming early in pregnancy. During these first few months, millions of neurons (brain cells) are produced deep inside the brain. These neurons must travel to the outer layer of the brain, called the cortex, where they begin to form networks. These networks can form the basis for our thinking, movement, and sensory processing.⁴

This journey, called neuronal migration, is guided by complex chemical signals and structural pathways. Between the 12th and 24th week of pregnancy, neurons migrate in waves, building the layers of the brain. If something disrupts this process, neurons may never reach their destination, resulting in an improperly formed cortex.⁵

When neurons get lost: How lissencephaly develops 

Detours and dead ends in brain development

In lissencephaly, something goes wrong within this process of neuronal migration. This means that neurons can get stuck, lost, or arrive at the wrong timing or location. This disruption can be caused by complications during pregnancy, such as genetic mutations or infections, resulting in impaired brain wiring. This is what causes the absence of gyri and sulci, giving the appearance of an abnormally smooth brain surface. The extent of the smoothness can vary, leading to different types and severities of the disorder.

Different types of lissencephaly

There are currently over 20 identified types of lissencephaly, which are generally categorised into two main subtypes: Type 1 (Classic) and Type 2 (Cobblestone) Lissencephaly.¹

Type 1 (classic) lissencephaly

• Usually happens because neurons fail to migrate properly during the 12th to 24th weeks of gestation⁶
• Results in a smooth or nearly smooth brain surface 

Type 1 lissencephaly is also associated with:

• Abnormally thick cerebral cortex 
• Four-layered cortex (normal cortex has six layers)
• Agyria (complete absence of gyri) or pachygyria (broad, flat gyri)⁶

Clinical features:

• Severe developmental delay
• Hypotonia progressing to spasticity
• Seizures, often early onset
• Feeding difficulties

Type 2 (cobblestone) lissencephaly

• Often part of a broader syndrome, such as Dandy-Walker Disease⁷

• Usually due to over-migration of neurons⁷
• Leads to a bumpy, cobblestone-like cortex instead of smooth gyri, giving it its name⁷

Clinical features:

• More severe than Type 1⁷
• Congenital muscular dystrophy
• Eye abnormalities
• Intellectual disability
• Seizures
• Early death is common

Why is lissencephaly so serious? 

The life-changing effects of a smooth brain

A smooth brain lacks the necessary architecture for complex neural communication. Due to neurons' placement not being in the right place, they can’t form proper networks, which can impact nearly every brain function, from movement and coordination to speech and thinking. 

Key Symptoms of lissencephaly

Children with lissencephaly often show symptoms shortly after birth. These may include:

• Severe developmental delays (e.g., inability or delay in sitting, crawling, or talking)
• Epileptic seizures, beginning in infancy
• Muscle tone abnormalities, such as stiffness (spasticity) or floppiness (hypotonia)
• Difficulty feeding and swallowing
• Vision problems and impaired motor skills
• Breathing difficulties, especially in more severe cases
• Abnormal facial appearance 

The condition’s impact on lifespan can vary, with some children living into adolescence or adulthood with supportive care, while others may face life-threatening complications earlier.

What causes the disruptions? 

Genes, infections, and more

The most common causes of lissencephaly are genetic mutations. More than 30 genes have been linked to this disorder^.8

• LIS1: Mutations in this gene are responsible for the majority of classic lissencephaly cases and are the most extensively studied. LIS1 helps control how neurons move¹ 
• DCX (Doublecortin): Often involved in lissencephaly in males and a milder condition called subcortical band heterotopia in females⁹
• ARX: This gene plays a key role in early brain development. It’s mutations are not only linked with lissencephaly, but also epilepsy, missing brain structures, and abnormal genital development¹⁰

These mutations are usually inherited, but they can also occur unexpectedly. In some cases, a parent may carry the mutation without showing symptoms, particularly in the case of DCX mutations passed from mother to son.¹¹

Environmental factors can also play a key role. Certain complications during pregnancy, such as insufficient oxygen delivery or infections such as cytomegalovirus (CMV) or toxoplasmosis, can damage fetal brain cells or interfere with migration signals. These non-genetic cases are sometimes referred to as "secondary" lissencephaly.¹,¹²

Diagnosing lissencephaly

How doctors spot it

The diagnosis of lissencephaly often begins when a child shows delays in development or starts having seizures. From there, doctors use neuroimaging tools, such as magnetic resonance imaging (MRI), to examine the brain’s structure.

MRI scans can clearly show the degree of smoothness in the brain and the thickness of the cortex, confirming the diagnosis. Further genetic testing can then be used to identify the specific gene involved in the disorder. This step can be helpful in future family planning and for better understanding disease outcomes.

In some cases, lissencephaly can be detected before birth through high-resolution ultrasounds or fetal MRI, particularly if there is a known family history or other risk factors.⁷

Is there a cure? 

Managing, not fixing the condition

Unfortunately, there is no cure for lissencephaly currently. However, although the damage to brain structure that occurs early in development cannot be reversed, the symptoms can be managed with support and care. 

Some typically offered options for patients are:

• Anticonvulsants to control seizures
• Physical and occupational therapy to improve muscle function and coordination
• Speech and feeding therapy to assist with swallowing and communication
• Nutritional support, which may include feeding tubes in severe cases
• Respiratory care for patients with breathing difficulties

Supportive care can significantly improve the quality of life for patients. In some cases, children with milder forms of lissencephaly can learn basic skills, although they may always need help with daily activities.

The future of lissencephaly research

Although lissencephaly remains incurable, research is making progress. Scientists are learning more about how genes and environmental factors affect neuronal migration, and this knowledge could be applied to discovering new treatments.

Some promising areas of research include:

• Gene therapy, which could one day correct faulty genes in early development
• Stem cell therapy, offers the potential to regenerate or repair damaged brain tissue
• Targeted drug therapies, aimed at supporting neuron migration in utero
• Better prenatal diagnostics, allowing earlier detection and intervention

Why neuronal migration matters

The process of building a brain is a very complex and delicate process, of which neuronal migration is fundamental. When this process goes wrong, as in lissencephaly, the results are profound. 

By understanding how and why neurons get lost, scientists and doctors can help formulate new treatments and care plans for people with lissencephaly, but also refine our understanding of how the brain is built. This knowledge can be extremely insightful and help in the fight against many other neurological disorders. 

While we can't yet cure lissencephaly, we can offer support, understanding, and hope to patients and keep pushing forward towards a future where fewer people suffer from this disorder.

Summary

• Lissencephaly is a rare brain disorder where the brain surface appears smooth due to disrupted neuronal migration during foetal development, leading to severe developmental problems
• Neuronal migration is the process by which neurons travel to their designated locations in the brain and is crucial for normal brain structure and function. Failure in this process results in a disorganized cortex and abnormal brain architecture
• There are two major types: Type 1 (Classic) and Type 2 (Cobblestone) Lissencephaly, which each have their distinct clinical characteristics
• Genetic mutations (e.g., in LIS1, DCX, ARX) and infections, alongside other environmental factors, are common causes of lissencephaly
• Lissencephaly diagnosis relies on MRI and genetic testing
• While there is no cure, early intervention, supportive therapies, and ongoing research in gene and stem cell therapy offer hope for improving quality of life and potential future treatments