Bilateral perisylvian polymicrogyria (BPP) is a rare neurological disorder that affects the cerebral cortex (the outer surface of the brain). BPP is a subtype of a broader condition known as polymicrogyria. The cerebral cortex of the brain normally consists of several deep folds and grooves. In BPP, the grooves that develop during embryonic growth form improperly on both sides of the brain near the Sylvian fissure, resulting in an increased number of folds that are unusually small. Signs and symptoms typically become apparent at birth, infancy, or later during childhood, and may include partial paralysis of the face, tongue, jaw, and throat; problems with speech and swallowing; excessive drooling; and seizures. Mild to severe intellectual disability often is also present. Some people with BPP have other health problems or birth defects. Most cases of BPP occur sporadically in people with no family history of BPP. Rarely, more than one family member has BPP, and the pattern of inheritance depends on the cause. Genetic causes may include mutations in single genes and contiguous gene disorders such as 22q11.2 deletion syndrome. BPP has also been reported in association with twin pregnancy complications. The diagnosis of BPP is based on the symptoms present and a thorough neurological evaluation including various imaging techniques. Treatment aims to address individual symptoms present in each person. For example, anti-seizure medications may help control seizures. The quality of life and life expectancy for people with BPP are not well-described but may depend on severity of symptoms, whether complications develop, and whether other birth defects or an underlying syndrome are present.

Contiguous gene disorders that have been associated with BPP include 22q11.2 deletion syndrome and 1p36 deletion syndrome.

Single gene disorders that have been associated with BPP include:

• MPPH syndrome - caused by a mutation in the AKT3, CCND2, or PIK3R2 genes
• Smith-Kingsmore syndrome - caused by a mutation in the MTOR gene
• MCAP syndrome - caused by mutations in the PIK3CA gene
• Lissencephaly - caused by a mutation in the TUBA1A gene
• Weaver syndrome - caused by a mutation in the EZH2 gene

Single genes in which mutations have been associated with BPP (but not necessarily a defined disorder or syndrome) include the EOMES, NEDD4L, and ADGRG1 genes.

In most cases, bilateral perisylvian polymicrogyria (BPP) occurs sporadically in people with no family history of BPP. Less commonly, BPP is inherited, and more than one family member may have BPP. The inheritance in each of these cases depends on the underlying cause of BPP and may be autosomal dominant, autosomal recessive, or X-linked.

• Partial paralysis of muscles on both sides of the face, tongue, jaw, and throat
• Sudden, involuntary spasms of facial muscles
• Excessive drooling
• Difficulty with sucking, chewing, and/or swallowing (dysphagia)
• Difficulty with speech (dysarthria)
• Seizures
• Mild spasticity of the limbs (spastic tetraplegia)
• Developmental delay or learning impairments
• Mild to severe intellectual disability
• Contractures present from birth (congenital)

Various other health problems or birth defects may occur in people with BPP, depending on whether an underlying genetic disorder with additional associated symptoms is present.