A study published in the Journal of Affective Disorders (2017) investigated whether a genetic predisposition to advanced biological ageing increases the risk of childhood-onset recurrent major depressive disorder (MDD) in a large UK sample. The research used Mendelian randomisation to assess if genetic variants associated with telomere length (TL) could predict MDD risk. The study focused on two single nucleotide polymorphisms (SNPs), rs10936599 and rs2736100, located in genes related to telomerase, an enzyme that maintains telomere length. The T-allele of rs10936599 was found to be associated with shorter TL and increased risk for childhood-onset MDD compared to controls and adult-onset MDD. The study found that genetic predisposition to advanced biological ageing, as indicated by these SNPs, was linked to a small but significant increase in the risk of childhood-onset recurrent MDD. The findings suggest that telomerase may be a potential target for preventing childhood-onset MDD. The study also highlights the importance of considering reverse causality in future research on the relationship between telomere length and MDD. Limitations include a relatively small sample of early-onset cases and reliance on retrospective recall for age-of-onset. The study underscores the potential role of genetic factors in biological ageing and their impact on mental health outcomes.A study published in the Journal of Affective Disorders (2017) investigated whether a genetic predisposition to advanced biological ageing increases the risk of childhood-onset recurrent major depressive disorder (MDD) in a large UK sample. The research used Mendelian randomisation to assess if genetic variants associated with telomere length (TL) could predict MDD risk. The study focused on two single nucleotide polymorphisms (SNPs), rs10936599 and rs2736100, located in genes related to telomerase, an enzyme that maintains telomere length. The T-allele of rs10936599 was found to be associated with shorter TL and increased risk for childhood-onset MDD compared to controls and adult-onset MDD. The study found that genetic predisposition to advanced biological ageing, as indicated by these SNPs, was linked to a small but significant increase in the risk of childhood-onset recurrent MDD. The findings suggest that telomerase may be a potential target for preventing childhood-onset MDD. The study also highlights the importance of considering reverse causality in future research on the relationship between telomere length and MDD. Limitations include a relatively small sample of early-onset cases and reliance on retrospective recall for age-of-onset. The study underscores the potential role of genetic factors in biological ageing and their impact on mental health outcomes.