It seems Dad’s age at conception-not Mom’s-may be the  primary predictor of whether a child develops a condition such as autism or  schizophrenia. 

 shows that as men age, the  number of new mutations in their sperm-and the likelihood that some of the  errors will be passed to offspring-increases. As a result, the worldwide trend  of men starting families later in life may be part of the reason why conditions  such as autism are on the rise. 

Researchers sequenced the genomes of 78 Icelandic families  with a child diagnosed with autism or schizophrenia and found that for every  year a man ages, 2 more new gene mutations appear in his offspring. They  calculated that the number doubles every 16.5 years from puberty onward,  meaning that 36-year-old men pass on twice as many mutations to their children  as do 20-year-olds. At what age this trend becomes problematic, however, is  impossible to know because many other factors affect children’s health and many  of the mutations are harmless. 

As women age, the researchers note, they are at greater risk  of having a child with Down syndrome or other rare chromosomal abnormalities,  yet men transmit about 4 times more new gene mutations to children. Experts  think this disparity may have something to do with the fact that men  continually make new sperm with the help of dividing precursor cells, which  acquire new mutations with every division.

It seems Dadâ€™s age at conceptionâ€”not Momâ€™sâ€”may be the primary predictor of whether a child develops a condition such as autism or schizophrenia.