Dysequilibrium syndrome

Description

Dysequilibrium syndrome (DES) is a group of disorders that are characterized by abnormal brain development, which causes intellectual disabilities and problems with balance and coordination (ataxia). The specific signs and symptoms and the severity of the condition can vary among affected individuals.

In people with DES, the part of the brain that coordinates movement (cerebellum) may be unusually small and underdeveloped (cerebellar hypoplasia). This can lead to ataxia that is present from birth and typically does not worsen over time. Additional brain abnormalities may include further loss of tissue (atrophy) in the cerebellum; fewer folds and grooves (gyri) on the surface of the brain; and a small brainstem, which is the area of the brain that connects the brain to the spinal cord.

Children with DES may have low muscle tone (hypotonia) and delayed development of motor skills such as walking. Some affected individuals learn to walk later in childhood, while others are never able to walk independently.

Additional features of DES may include intellectual disabilities that can vary from mild to profound; rapid, involuntary eye movements (nystagmus); and eyes that do not look in the same direction (strabismus). People with DES may also have difficulty speaking (dysarthria) or be unable to speak. Flat feet (pes planus), seizures, and short stature have been reported in some people with DES.

Frequency

The exact prevalence of DES is unknown, but more than 75 cases have been reported in the medical literature.

Causes

Certain variants (also called mutations) in one of several genes cause DES. There are at least four types of DES, each with a different genetic cause. Variants in the VLDLR gene cause a form of DES called type 1, also sometimes called VLDLR-related cerebellar hypoplasia. This is the most common form of DES.

The VLDLR gene provides instructions for making a protein called a very low-density lipoprotein (VLDL) receptor. This protein plays a critical role in guiding developing nerve cells to the appropriate locations in the brain. Many of the variants in the VLDLR gene that are associated with DES type 1 prevent cells from producing any functional VLDL receptor protein. Without this protein, developing nerve cells cannot reach the parts of the brain where they are needed. This impairs brain development, which leads to the intellectual disabilities and ataxia seen in people with this condition.

Variants in different genes cause the other types of DES and are each responsible for a small percentage of cases.

Inheritance

DES is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell must have a variant to cause the disorder. The parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but they typically do not show signs and symptoms of the condition.

Autosomal recessive inheritance. Credit: U.S. National Library of Medicine.

Other Names for This Condition

• CAMRQ
• CAMRQ syndrome
• Cerebellar ataxia, impaired intellectual development, and dysequilibrium syndrome
• Cerebellar ataxia-intellectual disability-dysequilibrium syndrome
• DES
• Non-progressive cerebellar ataxia-intellectual disability syndrome

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