What is Dandy-Walker syndrome?
Dandy-Walker syndrome is a condition that affects brain development, primarily development of the part of the brain that coordinates movement (the cerebellum). In individuals with this condition, various parts of the cerebellum develop abnormally, resulting in malformations that can be observed with medical imaging. The central part of the cerebellum, known as the vermis, is absent or very small. Cysts form in the fourth ventricle, which is a fluid-filled cavity between the brainstem and the cerebellum, causing the ventricle to enlarge. The part of the skull that contains the cerebellum and the brainstem, called the posterior fossa, is abnormally large. These abnormalities often result in problems with movement, coordination, intellect, and other neurological functions.
In 80 to 90 percent of individuals with Dandy-Walker syndrome, signs and symptoms caused by abnormal brain development appear within the first year of life. Most children have a buildup of fluid in the brain (hydrocephalus) that causes increased head size (macrocephaly). Affected individuals typically have intellectual disability that ranges from mild to severe, although some have a normal intellect. Children with Dandy-Walker syndrome often have delayed development, particularly a delay in motor skills such as crawling, walking, and coordinating movements. People with Dandy-Walker syndrome frequently experience muscle stiffness and paralysis of the lower limbs (spastic paraplegia), and they may also have seizures. Hearing and vision problems are sometimes a feature of this condition.
Less commonly, other brain malformations have been reported in people with Dandy-Walker syndrome. These malformations include a failure of the brain to divide properly into the right and left hemispheres (holoprosencephaly), underdeveloped or absent tissue connecting the left and right halves of the brain (agenesis of the corpus callosum), a sac-like protrusion of the brain through an opening at the back of the skull (occipital encephalocele), abnormal slits or clefts in the brain (schizencephaly), or a type of birth defect that occurs when the protective covering around the brain or spinal cord fails to close during development (neural tube defect). These additional brain malformations are associated with more severe signs and symptoms. It is estimated that 20 percent of individuals with Dandy-Walker syndrome survive past the first year of life. The most common causes of death in people with Dandy-Walker syndrome are problems related to hydrocephalus or complications of treatment.
Other signs and symptoms of Dandy-Walker syndrome can include heart defects, malformations of the urogenital tract, extra fingers or toes (polydactyly) or fused fingers or toes (syndactyly), or abnormal facial features.
In 10 to 20 percent of people with Dandy-Walker syndrome, signs and symptoms do not appear until late childhood or into adulthood. These individuals typically have a different range of signs and symptoms, including headaches, an unsteady walking gait, paralysis of facial muscles (facial palsy), increased muscle tone, muscle spasms, and mental and behavioral changes.
A milder form of Dandy-Walker syndrome, called Dandy-Walker variant, is associated with less severe brain abnormalities and, generally, less severe signs and symptoms. Rarely, people with brain malformations characteristic of Dandy-Walker syndrome have no symptoms.
How common is Dandy-Walker syndrome?
Dandy-Walker syndrome is estimated to affect 1 in 25,000 to 30,000 newborns.
What genes are related to Dandy-Walker syndrome?
Researchers have found mutations in a few genes that are thought to cause Dandy-Walker syndrome, but these mutations account for only a small number of cases. Dandy-Walker syndrome has also been associated with chromosomal abnormalities on most of the chromosomes. This condition can be a feature of some conditions in which there is an extra copy of one chromosome in each cell (trisomy). Dandy-Walker syndrome most often occurs in people with trisomy 18 (an extra copy of chromosome 18), but can also occur in people with trisomy 13, trisomy 21, or trisomy 9. Additionally, Dandy-Walker syndrome has been reported in fetuses or newborns with triploidy, a fatal condition in which individuals have a complete extra set of chromosomes in each cell. Dandy-Walker syndrome can also be a feature of genetic syndromes that are caused by mutations in specific genes. However, the brain malformations associated with Dandy-Walker syndrome often occur as an isolated feature (not associated with a genetic condition), and in these cases the cause is frequently unknown.
Research suggests that Dandy-Walker syndrome could be caused by environmental factors that affect early development before birth. For example, exposure of the fetus to infections, such as rubella or toxoplasmosis, or substances that cause birth defects (teratogens) may be involved in the development of this condition. In addition, a mother with diabetes is more likely than a healthy mother to have a child with Dandy-Walker syndrome.
How do people inherit Dandy-Walker syndrome?
Most cases of Dandy-Walker syndrome are sporadic, which means they occur in people with no history of the disorder in their family. A small percentage of cases of Dandy-Walker syndrome have been reported to run in families; however, the condition does not have a clear pattern of inheritance. Multiple genetic and environmental factors likely play a part in determining the risk of developing this disorder. First-degree relatives (such as siblings and children) of people with Dandy-Walker syndrome have an increased risk of developing the condition compared with people in the general population.
When Dandy-Walker syndrome is a feature of a genetic condition, it is inherited in the pattern of that condition.