How does parental age influence the likelihood of non-disjunction events?

Sourav PanNovember 8, 2024

Answered

Parental age significantly influences the likelihood of nondisjunction events, which can lead to chromosomal abnormalities such as Down syndrome. Here’s how age impacts these events:

Maternal Age

1. Increased Risk of Nondisjunction: As maternal age increases, the risk of nondisjunction during meiosis rises. This is particularly evident in women over the age of 35. Studies indicate that the risk of having a baby with a chromosomal abnormality, including Down syndrome (Trisomy 21), increases substantially with advancing maternal age. For instance, the risk is approximately 1 in 400 for women aged 30 and rises to about 1 in 100 for women aged 40.
2. Egg Quality and Quantity: Women are born with a finite number of eggs, and as they age, both the quantity and quality of these eggs decline. Older eggs are more likely to have chromosomal abnormalities due to accumulated damage over time, which can lead to errors during cell division (meiosis) and increase the likelihood of nondisjunction.
3. Statistical Evidence: Research shows that for every year a woman ages, the odds of chromosomal abnormalities such as Trisomy 21 increase significantly. For example, the relative risk (RR) for chromosomal abnormalities tends to increase four to seven times in women over 35 compared to those aged 25-29.

Paternal Age

1. Less Impact than Maternal Age: While paternal age does not have as pronounced an effect on nondisjunction as maternal age, there is evidence suggesting that older fathers may also contribute to genetic risks. Advanced paternal age has been associated with increased risks of certain conditions in offspring, including autism and schizophrenia, although the mechanisms are less well understood compared to maternal factors.
2. Sperm Quality: Unlike females, males produce sperm continuously throughout their lives. However, older paternal age can lead to genetic mutations in sperm due to accumulated DNA damage over time, potentially affecting offspring health