Detection of the β-codon 121 G-T mutation by restriction analysis. (a) A 497-bp fragment of β cDNA is amplified by the primers A (5′-TGA GGA GAA GTC TGC CGT TAC-3′ ) and B (5′-CCC CAG TTT AGT AGT TGG ACT TA-3′ ). The EcoRI restriction site is indicated by the arrow; this is abolished by the β-codon 121 mutation. EcoRI digestion produces 2 fragments of 347 and 150 bp from the normal allele, and a single uncut 497-bp fragment from the mutant allele. (b) Ethidium bromide–stained 2% agarose gels of electrophoresed EcoRI-digested β cDNA. The lanes are represented by M:ΦX174 RF DNA/HaeIII marker; 1, Uncut fragment; 2, case no. 2; 3, case no. 1; 4, positive control for codon 121 G-T; 5, normal control.