Findings from a study, featured in Nature Structural and Molecular Biology, bring together this unlikely combination that share commonalities, which may aid in future cognitive studies.
Both lactose intolerance and schizophrenia are inherited and make themselves known, not in the early years of life but years or even decades later.
Scientists from the Centre for Addiction and Mental Health in Toronto, Canada started to look at human and mouse small intestines.
By using DNA profiling and targeted bisulfite sequencing, the scientists were able to determine why the gene that code for the enzyme, lactase is ‘turned off’ with age in certain people but remains unaffected in others.
They found that genetic factors allowed the accumulation of genetic changes with age, therefore influencing the observable trait, in this case lactose intolerance.
The scientists believe that these principles could be applied to more complex mental illnesses such as schizophrenia, bipolar disorder or Alzheimer's disease.
These conditions also have DNA risk factors but take decades before clinical symptoms develop.
"The question we asked is why does this change happen over time? All newborns are able to digest lactose, independently from their genetic variation," said senior author Dr Arturas Petronis, head of the Krembil Family Epigenetics Laboratory at the Centre for Addiction and Mental Health (CAMH).
"Now, we know that epigenetic factors accumulate at a very different pace in each person, depending on the genetic variants of the lactase gene."
Over 65% of adults worldwide are lactose intolerant. The condition is influenced by only one gene, which determines if a person will lose the ability to process lactose over time.
Individuals with variants of this gene will gradually produce less lactase, the enzyme that breaks down lactose, as they age. Mental illness, although more complex, involve many more genes.
Essentially, the same molecular mechanisms may account for the delayed age of onset of illnesses, such as schizophrenia, in early adulthood, added Petronis.
Source: Nature Structural and Molecular Biology
Published online ahead of print, doi:10.1038/nsmb.3227
“Lactase nonpersistence is directed by DNA-variation-dependent epigenetic aging.”
Authors: Viviane Labrie et al.