4q21 microdeletion syndrome

4q21 microdeletion syndrome (also known as chromosome 4q21 deletion syndrome) is a rare chromosomal disorder caused by a submicroscopic deletion on the long arm of chromosome 4 at band q21. This contiguous gene deletion syndrome affects multiple body systems and is characterized by significant intellectual disability, severe speech and language delay or absence of speech, muscular hypotonia (low muscle tone), and distinctive facial features. Growth abnormalities, including both prenatal and postnatal growth restriction, are commonly observed, though some patients may develop obesity later in childhood. The characteristic facial features may include a broad forehead, hypertelorism (widely spaced eyes), flat nasal bridge, short nose with anteverted nares, thin upper lip, and low-set ears. Affected individuals frequently present with feeding difficulties in infancy related to hypotonia, and motor developmental milestones are typically delayed. Seizures have been reported in some patients. The severity of clinical features can vary depending on the size and exact location of the deletion, as well as which genes are encompassed within the deleted region. Several candidate genes within the 4q21 region, including PRKG2, RASGEF1B, and HNRNPD, have been proposed to contribute to the phenotype. There is currently no cure or targeted therapy for 4q21 microdeletion syndrome. Management is supportive and symptomatic, involving a multidisciplinary team approach. This may include early intervention programs, speech and language therapy, physical therapy for hypotonia and motor delays, occupational therapy, and special educational support. Seizures, when present, are managed with standard antiepileptic medications. Regular monitoring of growth and development is recommended, and genetic counseling should be offered to affected families.

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