GARS-AIRS-GART is crucial in studies of Down syndrome (DS)-related mental retardation due to its chromosomal location (21q22.1), involvement in de novo purine biosynthesis and over-expression in fetal DS brain postmortem samples. GARS-AIRS-GART regions important for structure-function were screened for mutations that might alter protein levels in DS patients. Mutation screening relied on multiplex/singleplex PCR-based amplification of genomic targets followed by amplicon size determination/fingerprinting. Serum protein samples were resolved by SDS-PAGE and immunoblotted with a GARS-AIRS-GART monoclonal antibody. No variation in amplicon size/fingerprints was observed in regions encoding the ATP-binding, active site residues of GARS, the structurally important glycine-rich loops of AIRS, substrate-binding, flexible and folate-binding loops of GART or the poly-adenylation signal sequences. The de novo occurrence or inheritance of large insertion/deletion/rearrangement-type mutations is therefore excluded. Immunoblots show presence of GARS-AIRS-GART protein in all patient samples, with no change in expression levels with respect to either sex or developmental age. © 2011 Association of Clinical Biochemists of India.