What is Heritability?
Definition
Essentially, heritability is an estimate of the contribution of genetic factors towards a particular trait – be it external (for example, height, hair color, complexion, etc.) or internal (such as intelligence) – or a specific disorder, like autism spectrum disorders or ADHD. Scientifically, it is defined as a statistical concept represented by “h²”. An estimate of heritability describes how much of the variation in a given trait can be credited to genetic variation, and thus is unique to one population in one environment, subject to change over time depending on the circumstances.
How it works
Historically, twin studies have been the preferred method of gauging heritability statistics. Identical twins share almost their entire DNA, whereas fraternal twins share about 50% of their DNA on average. If a trait appears to be more similar in the former than the latter, despite shared environmental specificities, the trait in question would be more likely to depend on genetic causes.
Estimates range from 0 to 1, with stats close to the least indicating that almost all of the variability in a trait among people depends more on environmental factors than the influence of genetic factors. The heritability of a majority of complex traits in people – including but not limited to multifactorial diseases – suggests an influence on variability by a combination of, both, genetic and environmental elements.
Misconceptions about Heritability
The term is frequently associated with the word “hereditary” in a loose connection between the two. However, this adds to the misunderstanding of heritability and relevant studies, often confusing the laymen who look up genetic variants contributing to a particular trait. Admittedly, being at the receiving end of mixed views from scientists themselves, heritability can be difficult to understand. Let us address a few prevalent misconceptions relevant to heritability:
- It does not indicate what proportion of a trait is determined by genes and what proportion is determined by the environment. Lee uses the example introduced by evolutionary biologist Richard Lewontin, where he establishes the image of planting similar seeds in uniformly optimal and uniformly suboptimal environments. In both cases, the heritability would be a 100%. This highlights that the heritability model is unable to count in the role of environmental components.
- It does not provide information about which genetic or environmental influences are at play, or their significance in determining the trait.
- Heritable is not the same as familial (shared by members of a family). Traits can appear in families for many reasons in addition to genetics. For instance, the language spoken can be categorized as a familial characteristic, but it has no genetic contribution.
- Heritability does not give any information about how easy or difficult it is to change a trait.
The Heritability of Autism Spectrum Disorder
Scientists suspect that autism spectrum disorder is a multifactorial condition. This implies that it is the result of a combination of environmental and genetic factors. This gives cause for researches into the heritability of the neurodevelopmental disorder.
Heritability Studies
The heritability estimates of autism shape relevant debate on nature vs nurture, according to Brian Lee, Associate Professor at Drexel University. It hints at which integrants contribute to the diagnosis of children of determination. Studies published from 2011 to 2014 estimated heritability to exist in the 35 to 50 percent range, while those published 2017 onwards observe a rise to 64 to 85 percent.
In a 2017 reanalysis study published by the JAMA Network, entitled “The Heritability of Autism Spectrum Disorder”, Sven Sandin et al. estimated that the role of genetics in causing ASD is 83%. To rebuke the previous analysis, this study involved 37 570 twin pairs, 2 642 064 full sibling pairs, and 432 281 maternal and 445 531 paternal half-sibling pairs. Of these, 14 516 children had an autism diagnosis. They concluded that environmental integrants played a minimal role is the cause of ASD.
The Limitations
Citing the rarity of the disorder and the time trends in its prevalence as limitations to their research, Sven Sandin et al. also mention the existence of “untestable assumptions” in twin and family methods of heritability research.
Heritability does not present us with a clear picture of how much of a condition is caused by genes, as it is often viewed. Rather, it highlights how much genetics predispose an individual to a particular condition, without factoring in how different environmental factors can activate said genetics. Lee, in his article, gives us the example of the heritability of height- it is estimated in humans to be about 80 percent, yet is still majorly regulated by the individual’s nutritional environment.
According to Lee’s analysis, there is mounting evidence in previous studies that suggests the inefficiency of the statistic model of heritability when understanding what causes autism. The model, he claims, does not factor in the influence of environmental factors on genetics. It poses as if genes and the environment are independent of each other, which is not quite the case. The reality is found to be more complex than the model, which sheds light on the inaccuracy of the results said model would produce. By excluding significant elements of causation, the study loses most credibility.
Heritability: What Causes Autism?
The heritability of Autism Spectrum Disorder highlights how the condition can be majorly influenced by genetic factors. It has been identified by studies to have an estimate of 83% contribution in predisposing an individual to ASD. However, the influence of environmental elements cannot be overlooked, though it is something that is commonly excluded from heritability studies due to the limitations of its statistical model. Regardless, Autism Spectrum Disorder has been established by researchers as a multifactorial condition. The heritability studies, not free from limitations of their own, provide a basis for further research for scientists to be able to break down complex traits for improved understanding. Consequently, heritability can help comprehend ASD better and hence shape autism treatment and methods of assistance in dedicated organizations, such as inclusion centers like Small Steps Big Dreams in Dubai UAE. The cause of autism may sound simple- an interplay of genetics and the environment- yet is more complex than the heritability statistical model can accommodate. It does, however, act as a stepping stone in the continuing research into exact causes of Autism Spectrum Disorder.