Ring chromosome 22

Lore & Background

Ring chromosome 22 was first described in 1968 by Lejeune et al., at a time when chromosomes 21 and 22 could not be differentiated and were both called the 'G chromosome'; ring 22 was initially termed 'G-deletion syndrome II'. Early reports debated whether it constituted a consistent syndrome or merely a finding in a heterogeneous group of intellectually disabled individuals. One notable early case involved monozygotic twin sisters with ring 22, among the first recorded shared chromosomal anomalies between twins.

Reader's Guide

Ring chromosome 22 is significant as a rare chromosomal disorder that illustrates the consequences of terminal deletions and ring formation on human development. Its phenotypic overlap with Phelan-McDermid syndrome highlights the critical role of the SHANK3 gene at 22q13.3, as individuals lacking this deletion may have normal phenotypes. The condition is diagnosed via karyotype and managed symptomatically with special education, speech therapy, and physical therapy. Although most cases arise sporadically, intergenerational transmission has been documented, including a three-generation family with variable expression. The disorder also shows an association with neurofibromatosis type II, particularly multiple meningiomas. Its legacy lies in clarifying genotype-phenotype correlations for chromosome 22 deletions and in demonstrating the instability and variable inheritance of ring chromosomes.

Did You Know?

• Ring chromosome 22 was first described in 1968 by Lejeune et al., when it was called 'G-deletion syndrome II'.
• Over half of a sample of 35 ring 22 patients were unable to speak, with a median age of 10.
• A family has been reported where ring chromosome 22 was passed down through three generations.
• Neurofibromatosis type II is associated with deletions of the NF2 gene on chromosome 22, not a typical feature of ring chromosome 22 syndrome.