To diagnose individuals homozygous for a &bgr;-thalassaemia
mutation ARMS primers for normal DNA are required so that
homozygous and heterozygous DNA can be distinguished.
Initially, the normal primer for IVSI ntl repeatedly gave a band
with DNA samples from patients homozygous for the IVSI ntl
mutation as determined by allele-specific oligonucleotide dot blot
analysis. The primer was re-made in the reverse direction with its 5’
end upstream of the mutation site. On retesting in combination with
common primer D it did not produce an amplified fragment with
DNA samples homozygous for the IVSI ntl mutation (data not
shown).