Assignment of human phosphoribosylglycinamide synthetase locus to region 21q221

The enzymatic activity of phosphoribosylglycinamide synthetase (GARS) has been studied in several cases of partial monosomies and full and partial trisomies 21. An excess of GARS activity was found in regular trisomy 21 with a trisomy 21/normal ratio equal to 1.55. A 0.99 ratio was found in 21q21----21pter monosomy; a 0.54 ratio was found in 21qter----21q22 monosomy; a 0.88 ratio, in 21q21----21pter trisomy, and a 1.46 ratio, in 21q22.1 trisomy. Consequently, the GARS gene locus, assigned to chromosome 21, could be localized in subband 21q22.1.