What is the typical number of trinucleotide repeats in the premutation range of fragile X?

The premutation range of fragile X syndrome is characterized by a specific number of trinucleotide repeats of the FMR1 gene. Typically, this range consists of 55 to 200 repeats of the CGG sequence. When individuals have repeats between 55 and 200, they are classified as premutation carriers, meaning they are at risk for producing offspring who may have a full mutation, which is associated with fragile X syndrome and involves more than 200 CGG repeats.

The significance of the premutation range lies in the potential for instability during DNA replication, which can result in the expansion of the number of repeats when passed from parent to child. Thus, individuals within this premutation range can transmit the condition to future generations.

In contrast, individuals with fewer than 55 repeats are considered to have normal alleles, while those with more than 200 repeats fall within the full mutation category, leading to the pathogenic effects of fragile X syndrome.