RAPID IDENTIFICATION OF MULTIPLE SUPERNUMERARY RING CHROMOSOMES WITH A NEW FISH TECHNIQUE

Multiple supernumerary ring chromosomes are a rare cytogenetic finding which is poorly understood. With the introduction of FISH techniques, their chromosomal origin can now be defined clearly. The techniques d escribed previously are complicated and time consuming. We report a ne w rapid technique which has been used to investigate two new cases. Mu ltiple probes were hybridised to a single slide by means of marking th e underside with a diamond pen to form a grid of squares, pipetting fi xed cell suspension into the centre of each square, forming a rubber s olution grid on the denatured, dehydrated slide following the Lines on the underside, adding a mixture of probes into each square, and seali ng the slide with a silicone rubber rim and a covering slide. The type of probe and the size, dimensions, and number of squares in the grid can be tailored to individual cases. The two new cases examined here a re mosaic for three (case 1) and four (case 2) supernumerary ring chro mosomes derived from different chromosomes. Normal cell lines were als o present. The karyotypes were established as 47,XY, 8,XY,+r(17),+r(20 )/49,XY,+r(4),+r(17),+r(20)/46,XY for case 1 and 47,XX, +r(4) /47,XX, +r(8)/47,XX, +r (10)/48,XX,+r(X),+r(4)/.../49,XX,+r(X),+r (8),+r(10)/4 6,XY for case 2. Our findings suggest that the ring chromosomes were f ormed during meiosis, perhaps involving complex rearrangements, result ing in a germ cell containing all markers, with subsequent loss of mar kers during cell division. Our second case also shows that the outcome is not invariably mental or physical handicap.