The clinical phenotype of patients with ring chromosome 22 includes mental
retardation with severe language impairment, hypotonia, and dysmorphic facial
features. In recent years an increasing number of patients with microscopic as
well as cryptic terminal deletion involving band 22q13 have been described and
their phenotype shows clinical features overlapping with patients with ring
chromosome 22. Loss of DNA in the 22q13.3 region may lead to a clinically
recognizable syndrome named "22q13.3 deletion syndrome." We report a patient with
a ring chromosome 22 who has hypotonia, profound mental retardation, language
impairment, dysmorphic features, and behavioral disorders. To check if the
critical region responsible for "22q13.3 deletion syndrome" was absent in this
ring, a fluorescent in situ hybridization (FISH) analysis using a probe
corresponding to the ARSA locus was performed. In our patient, only one ARSA
signal could be detected, indicating that the deletion encompassed the critical
22q13.3 region. A more detailed analysis of the deletion extent then was
performed using a panel of fluorescent probes located within 22q13. These
experiments allowed the identification of the breakpoint between CTA-299D3 and
RP5-925J7 probe, located in 22q13.32. Deletion extent could be estimated to be
about 2.5 Mb, and this larger deletion may explain the severity of clinical
features observed in our patient