Partial deletion of the long arm of chromosome 21 syndrome

Partial deletion of the long arm of chromosome 21 syndrome (also known as 21q partial monosomy or partial monosomy 21q) is a rare chromosomal disorder caused by the loss of a segment of genetic material from the long arm (q arm) of chromosome 21. The clinical presentation varies considerably depending on the size and precise location of the deleted segment. Unlike trisomy 21 (Down syndrome), which involves extra chromosome 21 material, this condition involves a deficiency of genetic material from the same chromosome. The syndrome can affect multiple body systems. Common clinical features may include intellectual disability of variable severity, growth retardation, craniofacial dysmorphism (such as microcephaly, broad nasal bridge, downslanting palpebral fissures, low-set ears, and micrognathia), skeletal anomalies, and congenital heart defects. Some patients may also present with thrombocytopenia or other hematologic abnormalities, particularly when the deletion involves the distal region of 21q that encompasses genes critical for platelet production and other developmental processes. Respiratory, gastrointestinal, and genitourinary anomalies have also been reported in some cases. There is no specific cure for this condition. Management is supportive and multidisciplinary, tailored to the individual's specific clinical manifestations. This may include early intervention programs, speech and physical therapy, cardiac surgery for congenital heart defects, and regular developmental monitoring. Genetic counseling is recommended for affected families to assess recurrence risk, which depends on whether the deletion arose de novo or was inherited from a parent carrying a balanced chromosomal rearrangement.

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