Ring chromosome 1 syndrome

Ring chromosome 1 syndrome (also referred to as ring chromosome 1, r(1) syndrome) is an extremely rare chromosomal disorder in which one copy of chromosome 1 forms a ring structure instead of its normal linear configuration. This occurs when both ends (the short arm, 1p, and the long arm, 1q) of chromosome 1 break off and the remaining segments fuse together in a circular form. The clinical consequences depend on the amount of genetic material lost during ring formation and the degree of ring instability, which can lead to mosaicism with monosomic or other aneuploid cell lines. The syndrome typically presents at birth or during early infancy with a combination of growth retardation (both prenatal and postnatal), intellectual disability of variable severity, microcephaly, and distinctive craniofacial features. Craniofacial findings may include a broad or flat nasal bridge, micrognathia, low-set or malformed ears, and hypertelorism. Additional features can include congenital heart defects, skeletal anomalies, and various other organ system malformations. The severity of the phenotype is highly variable and correlates with the extent of deleted chromosomal material and the proportion of cells carrying the ring chromosome. There is no specific cure or targeted therapy for ring chromosome 1 syndrome. Management is supportive and symptomatic, involving a multidisciplinary team that may include pediatricians, cardiologists, orthopedic specialists, neurologists, and developmental therapists. Early intervention programs, physical therapy, occupational therapy, and speech therapy are important components of care to optimize developmental outcomes. Genetic counseling is recommended for affected families to discuss recurrence risk and reproductive options.

Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.

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