In humans, insertion of retrotransposons has occasionally been associated with d
ID: 57074 • Letter: I
Question
In humans, insertion of retrotransposons has occasionally been associated with disease. An L1 element inserted into the gene for blood clotting fact VIII resulted in hemophilia in two separate individuals. An Alu insertion disrupted processing of an mRNA, resulting in neurofibromatosis in another person. In each case, the insertion was not present in the genotypes of either of the affected individual’s parents. Given that both of these elements are very common in human repetitive DNA, how is that examples of these spontaneous mutations are not more common?
Explanation / Answer
The retrotransposons L1 element and Alu are copy and paste gene sequences. They are very common in human repetitive DNA. They are capable of creating double stranded breaks in the DNA. The human replication and repair system is much efficient and upon identification of such replication errors rectify them immediately. Only under repair failured conditions, these sequences are responsible to cause mutations that result in genetic disorders. Thus, though these sequences are numerous in number in human genome they are not common examples of these spontaneous mutations.