The evaluation of eight chromosome 21 single copy sequences of the 21q22 region namely , SOD 1 , D21S15 , D21S42 , CRYA 1 , PFKL , CD 18 , COL6A1 , and S100B by a slot blot method showed in all three cases a partial deletion of 21q22 . 3 and partial monosomy . ^^^