Fathering children later in life increases risk for bipolar disorder in offspring
A Swedish study using data from the national registers found an increased risk for bipolar disorder (BPD) in the offspring of new fathers aged over 54. In particular, early-onset BPD was found to be closely linked with increasing paternal age. BPD is a brain disorder that causes unusually severe shifts in a person's mood, energy and ability to function. It typically develops in late adolescence or early adulthood, although it can occur during childhood or later in life. The symptoms of BPD range from euphoria and drug abuse to depression and chronic pain, and can lead to damaged relationships, impaired ability to function and suicide. It is widely accepted that a family history of psychotic disorders is one of the strongest contributing factors in BPD. However, there are few other known causes and a significant number of BPD patients have no family history of mental disorders. A large body of evidence suggests a link between paternal age and severe mental disorders, including schizophrenia and autism. This study is the first to examine the association between paternal age and BPD exclusively. Paternal age is thought to be a factor in some disorders because as men age, errors in the copying of DNA in their sperm increase. This is due to the fact that the cells that create sperm are replaced every 16 days. The significance of the resulting mutations has yet to be fully understood. In contrast, women are born with their full supply of eggs and, as a result, DNA copy errors do not occur in their eggs on the same scale. Researchers analysed data from 13,428 individuals in the Swedish national register who had been hospitalised for BPD and whose biological parents were both listed. Patients who had subsequently been hospitalised for schizophrenia were excluded from the analysis, and five controls were selected for each BPD patient. One of the study's main strengths is the very large sample size and the fact that BPD diagnosis and care has long been standardised across Sweden. In the current study the definition of BPD was narrow and inclusion criteria conservative. The study showed that after adjusting for maternal age, the risk of developing BPD increased with advancing paternal age across all age categories over 29 years. The highest risk was in the offspring of fathers older than 54. At the same time, maternal age was also seen to be a risk factor, especially in mothers between 35 and 39 years old. The main conclusions were that 'the risk of BPD was significantly higher in the offspring of older men compared with the offspring of younger men', and that the strong association between advancing paternal age and early-onset BPD 'supports the notion that, similar to other neurodevelopmental disorders, older paternal age increases the risk for de novo mutations in susceptibility genes for BPD'. The study, published in the Archives of General Psychology, was a collaboration between researchers at the Karolinska Institute in Stockholm, Sweden and at King's College London, United Kingdom.
Countries
Sweden, United Kingdom