Ageing: An X-linked trait? 17/2/04. By the Public Health Genetics Unit A Belgian study into the inheritance of telomere length proposes that key genes involved in ageing may be on the X chromosome.

Telomeres, specialised DNA sequences at the end of chromosomes, act as 'cap' to protect and stabilise the chromosome ends during replication. Human telomeres comprise tandem repeats of the sequence TTAGGG, and the overall telomere length (typically 15 000 base pairs at birth) decreases during every cycle of cellular replication, losing 25–200 base pairs per cell division. Eventually, once its telomeres have become critically short, the cell becomes senescent, and eventually dies.

Background: Telomeres

Previous research has suggested that telomere shortening and cellular senescence may be directly linked to the ageing process, and that shorter telomeres are associated with increased incidence of disease and risk of mortality. Twin studies have indicated that telomere length may be inherited.

This new study looked at telomere length in families from northern Belgium. Age had the most significant influence on length; men and smokers also tended to have shorter telomeres. But the most interesting correlations were within families – there were relationship in length between fathers and daughters, mothers and sons, and mothers and daughter. But, crucially, there was not a relationship in telomere length between fathers and sons.

The authors propose that the most plausible explanation for this correlation is an X-linked mechanism of inheritance for telomere length.

PHGU comment

This study provides sufficient evidence to warrant further investigation into the nature of inheritance of telomere length, which may also shed light on genetic factors that influence telomere length and ageing.

A better understanding of the mechanisms that underlie the ageing process is potentially of enormous value to medicine with respect to age related diseases and conditions, and also to cancer. For example, telomerase (an enzyme that replaces the TTAGGG repeats lost during cell division and allows indefinite cellular reproduction without ageing) is absent from normal somatic (non-reproductive) cells but found in around 90 per cent of human cancers.

Article courtesy of the Public Health Genetics Unit .

Further reading

Nawrot T S, et al (2004) Telomere length and possible link to X chromosome. Lancet 2004; 363: 507-10. Abstract