SummaryWe have. id.entified a partial deletiotl of the 8hart arm of chromosome 20 in a .5-ye.0r~-o!d boy from pareu.t~ having norm~! phenotype and ka~otype, Hi~ major anomalies were mild .mer~tal retardation, eongenita! be.art di~sease., chest deformity, s~pina bifido, kyphosco!io~is, inguinal hernia, and preaurjcula.r fistula, Th# c.lin, ic0! findings were tompared with those of two patLe0t~ r~eport~d pre~viou_s!y o~ a partial deletion 20p.T~ activity of adeno.sine deamin.ase in the patJent'~ red blood r162 was within normal range, sugge~sting that the gene. locus for the enzyme, which has been pr~evioosly as_signr to ~hromosom~ 20, may not pre.sent on pl !--*pter of chromosome 20,