Rapid detection of microdeletions using fluorescence in situ hybridisation (FISH) on buccal smears

Editor—Use of buccal smears for the detection of numerical sex chromosome abnormalities has long been known. The facultative heterochromatin of the inactive X chromosome in the normal female is visible in Giemsa stained interphase nuclei as a condensed body, the Barr body.1 The active X is not visible. The constitutive heterochromatin of the long arm of the human Y chromosome, which varies greatly in size between people, is visible as a fluorescent body in interphase nuclei stained with quinacrine. More recently, FISH using centromere probes has been applied to interphase nuclei of buccal mucosa for the study of oral cancers,2-4 for detection of supernumerary i(12p) and i(18p) chromosomes,5 6 and for the detection of chromosomal sex.7 8 Although patients with Williams syndrome (WS) and 22q11 deletion syndrome have a normal standard karyotype, a submicroscopic deletion can be found in both syndromes using FISH. We report the use of FISH on buccal smears using cosmid probes for 7q11.23 (WS) and 22q11.2 (22q11 deletion syndrome) for the rapid detection of these two microdeletion syndromes. Six patients known to have a microdeletion (three 7q11 and three 22q11) were compared to eight healthy controls. All the patients had been previously diagnosed by FISH on metaphase chromosomes of peripheral blood samples. Buccal smears were obtained by standard methods. FISH was carried out with Vysis LSI dual colour probes. With the …