The same genes thought to make people clever may also lead to anorexia, autism and bipolar disorder, a major study claims.

The largest ever investigation into genetic links between 25 brain disorders delved into the genomes of one million patients.

Massachusetts Institute of Technology and Harvard researchers were surprised at what they uncovered from their ‘unprecedented’ effort.

They found the same genetic factors that predispose people to certain psychiatric conditions are linked to spending more years in school and educational attainment.

However the scientists also suggested the same ‘clever genes’ could protect against Alzheimer’s.

Dr Benjamin Neale, study co-author, said: ‘This work is starting to re-shape how we think about disorders of the brain.

‘If we can uncover the genetic influences and patterns of overlap between different disorders, then we may be able to better understand the root causes of these conditions.’

He added this could also ‘potentially identify specific mechanisms appropriate for tailored treatments’.

The study, published in ‘Science’, pooled genetic data to examine the patterns across 25 psychiatric and neurological conditions.

Huge sample sizes were needed to help separate reliable signals from noise as each genetic variant carries only a tiny risk of leading to a condition.

Exploring these biological connections is challenging. The brain is a tricky organ to study directly, difficult to scan in detail or ethically biopsy.

And, because brain disorders often co-occur, it’s hard to untangle when one may be affecting the development of another.

To get around this, researchers measured the amount of genetic overlap across the disorders using genetic data from 265,218 patients and 784,643 controls.

They also examined relationships between brain disorders and 17 other measures, such as years of education, from nearly 1.2 million individuals.

Dr Verneri Anttila, study co-author, said: ‘This was an unprecedented effort in sharing data... to improve our understanding of the brain.’

The final results indicated a widespread genetic overlap across different types of psychiatric disorders.

But the strongest overlap was noted between ADHD, bipolar disorder, depression and schizophrenia.

A similar link was also discovered between anorexia and OCD, and between OCD and Tourette’s syndrome.

In contrast, neurological disorders such as Parkinson’s and multiple sclerosis were more distinct from one another and from the psychiatric disorders.

However, migraine was genetically correlated to ADHD, depression and Tourette’s syndrome, according to the researchers.

Additionally, the researchers were surprised to find genetic factors predisposing individuals to anorexia, autism, bipolar, and OCD were linked to spending more years in school and educational attainment.

Neurological disorders, however, particularly Alzheimer’s and stroke, were negatively correlated with those same cognitive measures.

Dr Anttila added: ‘We’ll need more work and even larger sample sizes to understand these connections.’

Agencies