Picture: Megan Powell/The West Australian

From the moment we are born each of us is dealt a hand that one day might play a part in shaping our success, health and personality. The time of year, how wealthy and how old our parents are, the order we are born and even where we are born have all been identified as factors influencing who we might one day become, and for some serious researchers this points the way to causes of disease.

Season of birth, season of conception, even the latitude of where you are born are offering tantalising epidemiological clues to underlying contributors to diseases including schizophrenia, multiple sclerosis and autism.

Speculation about the cause of these links has ranged from vitamin D exposure during pregnancy, seasonal infections, changes in nutrition and even weather fluctuation.

Babies born in winter or spring have an 11 per cent increased risk of having schizophrenia as an adult, according to schizophrenia researcher John McGrath, from the Queensland Brain Institute.

Having studied the vitamin D effect, Professor McGrath said evidence supported the idea that not enough vitamin D during pregnancy could influence later life schizophrenia for the unborn child.

Latitude was another factor that appeared to play a role in disease later in life. Professor McGrath said there were a number of diseases which appeared to be influenced by the latitude at which people were born, with multiple sclerosis (MS) the most famous example.

"If you are born in high latitude then you have a much higher risk of getting MS. In Queensland we have less MS than Tasmania - that's made people scratch their heads and think what on earth is going on and probably it is vitamin D as well," he said.

Even anorexia appears to be influenced in some way by season of birth, with UK researchers finding those born in spring were more likely (15 per cent) to develop the condition.

"Those of us trying to prevent debilitating disease, we do look at things like season of birth and latitude and they are giving us clues in disorders like multiple sclerosis and schizophrenia, very solid convincing clues pointing to vitamin D," Professor McGrath said.

"That's good news because all of a sudden you think can do something about this."

Paternal age can also influence disease, with strong links between older dads and various disorders including schizophrenia and autism.

The age of a child's grandfather when he had the father or the mother of the baby also seemed to play a role in the development of schizophrenia, with mutations passed down through the generations.

"This is also a non-trivial issue because our society is delaying parenthood and we are seeing some unexpected consequences that are coming through from epidemiology," he said.

Telethon Institute for Child Health Research (TICHR) autism researcher Andrew Whitehouse said time of conception, rather than season of birth, was associated with a small increased risk of autism, and again vitamin D was being examined as a likely culprit.

"The season of conception effect increases the further you get away from the equator because the sun exposure varies a lot more depending on how far away you are, so if you are in Perth compared with Broome you are going to see a larger season of conception effect," he said.

Birth order, while perhaps not as significant for the development of future disease, also offered some interesting insights into personality and intelligence and for boys perhaps even whether they would be gay, Professor Whitehouse said.

The idea that birth order influenced the type of people we were destined to become had been around for centuries, with little hard evidence to support the stereotypes that first-born children were the leaders, middle children the negotiators and last- borns the non-conforming rebels.

However, there was evidence showing the sooner your arrival in the family, the smarter you were likely to be, Professor Whitehouse said.

First-borns were generally smarter and more conscientious than their latter-born siblings. Although there were only a few IQ points in it, studies had shown that successive children were marginally less intelligent than those who preceded them.

The likely cause was nurture rather than genetics, with studies of families whose first-born child had died showing the second-born, who assumed the social role of the first-born, with a higher intelligence score in line with that of a first-born.

Professor Whitehouse said how we raised our children, how we educated them and loved them would always trump whatever small effect birth order might have.

"Ultimately, these small effects are likely to be dwarfed by the absolute fundamental positive influence of a nurturing environment when a child is born, there is nothing that can beat that," Professor Whitehouse said.

US research revealed birth order could also influence who we chose as friends, with first-borns more likely to be friendly with first-borns, middle-borns with middle-borns and last-borns with last-borns, indicating birth order could indeed play a role in personality.

A Canadian researcher found boys with older brothers were more likely to be homosexual than those with sisters, younger brothers or no siblings.

However, the cause of the finding is unknown, with speculation that it could be related to exposure to hormones prenatally or the environment the child was brought up in.

Steve Zubrick, head of population sciences at TICHR, said that, broadly speaking, children who were born into families of high socio-economic status were likely to have an easier path to success.

Their parents had higher expectations of them but also the means to help them fulfil those expectations.

"For families in other circumstances it is a harder reach, it doesn't mean it is impossible, but other sacrifices have to be made," Professor Zubrick said.

Parental age was also a factor in outcomes for children, with those born to teenage parents facing challenges to their development, more so than those born to older, more mature parents.

"The risks of childbearing are very high. The risks for good onward child development are very high," he said.

Children of sole-parent families, where there was usually less income, were also likely to have to jump more hurdles to succeed.

Professor Zubrick said it was important to note that children were not born into a straitjacket, with their life pre-determined on the day they were born.

Millions of people had overcome the odds stacked against them.

US research revealed birth order could also influence who we chose as friends.

The West Australian

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