Polymicrogyria

Also known as: PMG

Definition

Genetics Home Reference

Polymicrogyria is a condition characterized by abnormal development of the brain before birth. The surface of the brain normally has many ridges or folds, called gyri. In people with polymicrogyria, the brain develops too many folds, and the folds are unusually small. The name of this condition literally means too many (poly-) small (micro-) folds (-gyria) in the surface of the brain.

Polymicrogyria can affect part of the brain or the whole brain. When the condition affects one side of the brain, researchers describe it as unilateral. When it affects both sides of the brain, it is described as bilateral. The signs and symptoms associated with polymicrogyria depend on how much of the brain, and which particular brain regions, are affected.

Researchers have identified multiple forms of polymicrogyria. The mildest form is known as unilateral focal polymicrogyria. This form of the condition affects a relatively small area on one side of the brain. It may cause minor neurological problems, such as mild seizures that can be easily controlled with medication. Some people with unilateral focal polymicrogyria do not have any problems associated with the condition.

Bilateral forms of polymicrogyria tend to cause more severe neurological problems. Signs and symptoms of these conditions can include recurrent seizures (epilepsy), delayed development, crossed eyes, problems with speech and swallowing, and muscle weakness or paralysis. The most severe form of the disorder, bilateral generalized polymicrogyria, affects the entire brain. This condition causes severe intellectual disability, problems with movement, and seizures that are difficult or impossible to control with medication.

Polymicrogyria most often occurs as an isolated feature, although it can occur with other brain abnormalities. It is also a feature of several genetic syndromes characterized by intellectual disability and multiple birth defects. These include 22q11.2 deletion syndrome, Adams-Oliver syndrome, Aicardi syndrome, Galloway-Mowat syndrome, Joubert syndrome, and Zellweger spectrum disorder.

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Orphanet

Polymicrogyria (PMG) is a heterogenous group of cerebral cortical malformations characterized by excessive cortical folding and abnormal cortical layering that, depending on its topographic distribution, presents with variable combinations of neurological symptoms of varying severity such as epilepsy, developmental delay, intellectual disability, motor dysfunction (e.g. spasticity), and pseudobulbar palsy

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Symptoms

Medical Term Other Names Description
Seizures Epilepsy Seizures are an intermittent abnormality of the central nervous system due to a sudden, excessive, disorderly discharge of cerebral neurons and characterized clinically by some combination of disturbance of sensation, loss of consciousness, impairment of psychic function, or convulsive movements. The term epilepsy is used to describe chronic, recurrent seizures.
Pseudobulbar paralysis Pseudobulbar palsy Bilateral impairment of the function of the cranial nerves 9-12, which control musculature involved in eating, swallowing, and speech. Pseudobulbar paralysis is characterized clinically by dysarthria, dysphonia, and dysphagia with bifacial paralysis, and may be accompanied by Pseudobulbar behavioral symptoms such as enforced crying and laughing.
Spasticity Muscle spasticity, Muscular spasticity A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with increased muscle tone, exaggerated (hyperexcitable) tendon reflexes.
Muscle weakness Muscular weakness Reduced strength of muscles.
Strabismus Squint, Heterotropia, Cross-eyed, Squint eyes [more] Strabismus (also known as squint) is a condition in which the eyes are not properly aligned with each other.
Polymicrogyria A congenital abnormality of the cerebral hemisphere characterized by an excessive number of small gyri (convolutions) on the surface of the brain.
Global developmental delay Psychomotor developmental delay, Psychomotor retardation, Developmental delay, Lack of psychomotor development, Cognitive delay, Delayed intellectual development, Delayed milestones, Psychomotor development deficiency, Developmental retardation, Motor and developmental delay, Developmental delay in early childhood, Retarded psychomotor development, Retarded mental development, Delayed cognitive development, Retarded development, Delayed developmental milestones, Delayed development, Psychomotor development failure, Mental and motor retardation, Psychomotor delay, Delayed psychomotor development [more] A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.
Paralysis Inability to move Paralysis of voluntary muscles means loss of contraction due to interruption of one or more motor pathways from the brain to the muscle fibers. Although the word paralysis is often used interchangeably to mean either complete or partial loss of muscle strength, it is preferable to use paralysis or plegia for complete or severe loss of muscle strength, and paresis for partial or slight loss. Motor paralysis results from deficits of the upper motor neurons (corticospinal, corticobulbar, or subcorticospinal). Motor paralysis is often accompanied by an impairment in the facility of movement.
Intellectual disability Nonprogressive intellectual disability, Poor school performance, Mental-retardation, Dull intelligence, Nonprogressive mental retardation, Mental deficiency, Mental retardation, nonspecific, Low intelligence [more] Subnormal intellectual functioning which originates during the developmental period. Intellectual disability, previously referred to as mental retardation, has been defined as an IQ score below 70.

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