Partial deletion of chromosome 1 syndrome

Partial deletion of chromosome 1 syndrome (Orphanet code 261766) is a broad category encompassing rare chromosomal disorders caused by the loss (deletion) of a segment of chromosome 1. Because chromosome 1 is the largest human chromosome and contains a large number of genes, the clinical presentation varies considerably depending on the size and precise location of the deleted segment (short arm 1p or long arm 1q). This condition is also referred to as partial monosomy of chromosome 1. Affected individuals commonly present with intellectual disability of variable severity, developmental delay (motor and speech), growth retardation, and distinctive craniofacial features that may include microcephaly, broad or flat nasal bridge, low-set ears, and micrognathia. Depending on the specific region deleted, additional features may include congenital heart defects, skeletal anomalies, seizures, visual or hearing impairment, and genitourinary malformations. Multiple organ systems can be involved, including the central nervous system, cardiovascular system, musculoskeletal system, and urogenital system. Most cases arise de novo (as new events not inherited from a parent), though some may result from unbalanced segregation of a parental balanced chromosomal rearrangement such as a translocation. Diagnosis is established through chromosomal analysis, including karyotyping, FISH, or chromosomal microarray. There is no cure for partial deletion of chromosome 1 syndrome; management is supportive and symptom-based, involving early intervention programs, physical and occupational therapy, speech therapy, and medical or surgical treatment of specific complications such as cardiac defects or seizures. Genetic counseling is recommended for affected families to assess recurrence risk.

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