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The role of the MUC 1 mucin gene in infertility
  
By Bijal P. Trivedi


A recent study leads some researchers to believe that variations in the size of the mother's MUC 1 mucin gene may affect her embryo's ability to implant in the uterus.

In general all of the 20 women in the study carried one copy of the MUC 1 gene that contained about 5,200 nucleotides. The second copy of the gene appeared to vary between the ten fertile and ten infertile women.

Researchers led by El-Nasir Lalani, of Imperial College School of Medicine, in London, found that the average length of the second MUC 1 gene in women with at least two successful, uneventful, full-term pregnancies was 3,400 nucleotides. Women who were infertile due to suspected problems with embryo implantation carried a second MUC 1 gene that was on average shorter, with 2,500 nucleotides.

While the factors that are essential for successful embryo implantation are not well understood, Lalani suggest that MUC 1 may be involved. The MUC 1 gene produces a long protein that is embedded in the outer surface of the cells make up the endometrium, the innermost layer of the uterus. The MUC 1 protein is long and probably extends far off the surface of the cell. Lalani and her colleagues suggest that the MUC 1 protein might be one of the first molecules that the embryo encounters as it tries to attach to the lining.

The gene length can vary because it contains a variable number tandem repeat (VNTR) region. VNTRs are made up of short DNA sequences that are repeated over and over. In the fertile women, the second copy of the MUC 1 gene contained 55 repeating units of DNA. In infertile women the number of repeating units was 40.

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Horne, A.W. et al. MUC 1: a genetic susceptibility to infertility? Lancet 357, 1336-1337 (April 28, 2001).
 

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