An adenine trimer precedes a C/G polymorphism in the 3'-amplimer region of the human platelet glycoprotein IIIa intron 6 CT repeat.

Restriction enzyme and short tandem repeat polymorphisms are often used to link a particular allele with an inheritable disease-related gene in the absence of the information regarding the DNA mutation or defect. Polymorphic markers within the gene in question are particularly useful and can provide sufficient information for genetic counselling to potential carriers of the disease. Using a published method for the CT repeat in intron 6 of the GP3A gene, it was found that a single nucleotide deletion in the published genomic GP3A sequence in the region of the antisense amplimer and a C/G nucleotide polymorphism (allele frequencies, G = 0.883, C = 0.117) immediately adjacent to the deletion were responsible for the lack of PCR amplification. The absence of amplification has important implications for the assignment of a particular CT repeat to a given allele and for the population frequencies of the various CT repeats.