Aicardi syndrome is a rare genetic disorder that affects the brain, eyes, and spine, occurring almost exclusively in girls. It strikes roughly 1 in 105,000 live births in the United States and is defined by three hallmark features: a missing or underdeveloped connection between the two halves of the brain, seizures that begin in infancy, and distinctive lesions on the retina. Most cases are identified within the first few months of life, when seizures first appear.
The Three Defining Features
Diagnosis hinges on what doctors call the “classic triad.” The first feature is a partial or complete absence of the corpus callosum, the thick band of nerve fibers that lets the left and right sides of the brain communicate. In about 70% of cases, this structure is entirely missing. In the remaining 30%, it is partially formed. Rare individuals with the syndrome have a normal corpus callosum, but this is the exception.
The second feature is infantile spasms, a type of seizure that typically begins between 3 and 5 months of age. These look like sudden, brief stiffening of the body, often in clusters. Over time, seizure patterns frequently change and can become harder to control, often requiring multiple medications.
The third feature is chorioretinal lacunae: round, flat, yellowish-white spots found on the retina, usually clustered near the optic nerve. They range from about half to three times the size of the optic disc. These lesions don’t grow or multiply over time and generally don’t impair vision unless they happen to sit directly over the central point of focus. In a study of 40 girls with the syndrome, 39 had these retinal spots in one or both eyes. While they are closely associated with Aicardi syndrome, they have occasionally been found in other conditions as well.
Why It Affects Almost Only Girls
Aicardi syndrome is believed to result from a spontaneous mutation on the X chromosome, meaning it isn’t inherited from a parent. The specific gene has not yet been identified, but the pattern is consistent: because girls have two X chromosomes, one normal copy can partially compensate for the mutated one, allowing survival. In boys, who have only one X chromosome, the mutation is nearly always fatal before birth. The rare confirmed male cases have involved boys with an extra X chromosome (47,XXY), which provides that same compensating copy.
The random way cells “switch off” one of their two X chromosomes also explains why the syndrome looks so different from one girl to the next. Depending on which cells happen to silence the healthy copy versus the mutated copy, the effects can range from relatively mild to severe.
Brain Abnormalities Beyond the Corpus Callosum
The brain changes in Aicardi syndrome extend well beyond the missing connection between hemispheres. Brain imaging commonly reveals several additional structural problems. Polymicrogyria, a condition where the brain’s surface has too many abnormally small folds, is frequently found, particularly around the front of the brain. Clusters of nerve cells that failed to migrate to their correct position during fetal development (called heterotopias) are also common. Fluid-filled cysts within the brain, underdevelopment of the cerebellum (the region that coordinates movement), and noticeable asymmetry between the two sides of the brain round out the picture.
This constellation of findings, particularly frontal polymicrogyria combined with misplaced nerve cell clusters and intracranial cysts, is distinctive enough that radiologists may flag it as a reason to investigate Aicardi syndrome specifically.
Other Eye Findings
While the retinal lacunae are the signature eye feature, the full range of eye involvement varies widely. Some girls have nearly normal eyes aside from the lacunae. Others may have underdeveloped optic nerves, abnormally small eyes, or misaligned eyes (strabismus). An ophthalmology evaluation is a key part of the diagnostic process and ongoing care.
How the Diagnosis Is Made
There is no single blood test or genetic test that confirms Aicardi syndrome. Diagnosis requires a team effort among neurologists, ophthalmologists, and radiologists. The process typically starts when a young infant presents with seizures. An MRI of the brain reveals the absent or malformed corpus callosum along with other structural abnormalities. An eye exam identifies the characteristic retinal lacunae. An EEG (brain wave recording) documents the seizure activity. All three elements of the classic triad must be present for a definitive diagnosis, though revised criteria also recognize the broader brain malformations as major supporting findings.
Prenatal diagnosis is not reliably possible because the retinal lesions and seizure activity cannot be assessed before birth. Brain cysts detected on a prenatal ultrasound may raise suspicion, but confirmation has to wait until after delivery.
Skeletal and Other Physical Issues
Aicardi syndrome is not limited to the brain and eyes. Many affected girls develop abnormalities of the ribs and spine, collectively called costovertebral defects. Scoliosis is a particular concern, especially for girls who are not independently mobile, and it may require orthopedic monitoring and intervention to prevent complications.
Feeding difficulties are common. Many children experience trouble swallowing and may need a modified diet or feeding therapy. Some eventually require a surgically placed feeding tube to maintain adequate nutrition. Constipation and other bowel issues are also frequent and typically managed with stool softeners or similar medications.
Developmental Expectations
All children with Aicardi syndrome experience some degree of intellectual disability and developmental delay, but the severity varies. On the more affected end of the spectrum, children may have very limited head control, no independent movement, and no communication beyond a social smile. Girls with milder involvement may achieve floor mobility, some spoken words, or the ability to walk with assistive devices. The degree of brain malformation and how well seizures respond to treatment are major factors shaping each child’s developmental trajectory.
Seizure Management and Ongoing Care
Seizures are often the most challenging aspect of daily management. Most girls need multiple anti-seizure medications, and the types of seizures may shift over time, requiring adjustments. Recent studies have shown that cannabidiol-based treatments can reduce seizure frequency by up to 50% in some patients. Despite treatment, complete seizure control is uncommon.
Beyond seizure management, care is highly supportive and multidisciplinary. Physical and occupational therapy help maintain flexibility, prevent joint contractures, and maximize whatever mobility is possible. Positioning devices, wheelchairs, and other adaptive equipment are often part of daily life. Vision services through early intervention programs or school districts can support learning. Regular monitoring by an orthopedist tracks spinal curvature and hip stability, particularly in children who are not walking.
Life Expectancy
Aicardi syndrome significantly shortens life expectancy. The median survival is around 18 years. Early reports suggested only about 40% of individuals survived to age 15, but more recent data paint a somewhat more hopeful picture, with survival rates reaching approximately 60% at age 27. Pneumonia is the most common cause of death, reflecting the breathing and swallowing difficulties that accompany severe neurological impairment. Some individuals do live into their twenties and beyond, particularly those with milder brain involvement and strong supportive care.