CRYPTIC TERMINAL REARRANGEMENT OF CHROMOSOME 22Q13.32 DETECTED BY FISH IN 2 UNRELATED PATIENTS

Two unrelated patients with cryptic subtelomeric deletions of 22q13.3 were identified using FISH with the commercially available Oncor probe , D22S39. Proband 1 was found to have a derivative chromosome 22 resul ting from the unbalanced segregation of a t(1;22)(q44;q13.32) in her m other. Additional FISH analysis of proband 1 and her mother placed the breakpoint on chromosome 22 in this family proximal to D22S55 and D22 S39 and distal to D22S45. We have mapped D22S39 to within 170 kb of D2 2S21 using pulsed field gel electrophoresis. D22S21 is genetically map ped between D22S55 and D22S45. These data indicate that the deletion i n proband 1 is smaller than in eight of nine reported del(22)(q13.3) p atients. Probands 1 and 2 share features of hypotonia, developmental d elay, and expressive language delay, also seen in previously reported del(22)(q13.3) patients, although proband 1 appears to be more mildly affected. Proband 1 is also trisomic for the region 1q44-->qter. This very small duplication has been previously reported only once and the patient had idiopathic mental retardation. This is the first report wh ere 22q13.3 terminal deletion patients have been identified through th e use of FISH, and the first report of a deletion of this region occur ring because of missegregation of a parental balanced cryptic transloc ation. We feel that investigation of the frequency of del(22) (q13.3) in the idiopathic mentally retarded population is warranted and may be aided by the ability to use a commercially available probe (D22S39), which is already currently in use in a large number of cytogenetic lab oratories.