Detection of unstable trinucleotide repeats

Unstable trinucleotide repeats are a newly recognized class of disease mutation. Several major human single gene disorders are now attributed to expansions of these highly unstable sequences (1-4). Their molecular analysis is particularly challenging, since: 1. Accurate allele sizing is essential; 2. Polymerase chain reaction (PCR) amplification across the repeat is hampered by extreme guanme cytosme (GC) content and strong secondary structure, and 3. Size differences between normal and mutated alleles may be great, for instance, in fragile X they can range from 6 to over 1000 repeats.