Genetic variations in height plus other factors

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Genetic variations in height plus other factors

The hereditary traits make up the composition of a certain individual. Necessary genetic sequence has been the basis of many researches to configure the human genome and its constitution.


Height Variations

Scientists estimate that about 80 percent of an individual’s height is determined by the DNA sequence variants they have inherited, but which genes these variants are in and what they do to affect height are only partially understood.

Height and genetics are presumably related and inheritable. However, certain mutations could arise to growth problems and other disorders physically. Some rare gene mutations have dramatic effects on height (for example, variants in the FGFR3 gene cause achondroplasia, a rare condition characterized by short stature).

For most individuals, height is controlled largely by a combination of genetic variants plus a smaller contribution from environmental factors (such as nutrition).

Some of these variants are in genes that directly or indirectly affect cartilage in growth plates, which are areas in the long bones of the legs and arms where new bone is produced, lengthening the bones as children grow.

In addition to the FGFR3 gene, researchers have identified hundreds of other genes involved in rare disorders that have an extreme effect on height. These genes include FBN1 which causes Marfan syndrome and dysplasia, GH1 the gene which causes growth hormone deficiency, and GPC3 which is associated with Simpson-Golabi-Behmel syndrome.

Furthermore, a disease named EVC (Ellis-van Creveld syndrome) also causes Weyers acrofacial dysostosis.

Some genes, such as ACAN, contain rare variants that cause severe growth disorders, which affects height without a related health condition. Identifying other height genes, is an active area of genetic research which scientists continue to conduct.

Because height is determined by multiple gene variants (an inheritance pattern called polygenic inheritance), it is difficult to accurately predict how tall a child will be. The inheritance of these variants from one’s parents helps explain why children usually grow to be approximately as tall as their parents, but different combinations of variants can cause siblings to be of different heights. Height is influenced by other biological mechanisms (such as hormones) that may also be determined by genetics, although the roles of these mechanisms are not fully understood.

In addition to genetic and biological determinants, height is also influenced by environmental factors, including the nutritional status of the mother during pregnancy, smoking, drugs, and her exposure to hazardous substances. A well-nourished, healthy, and active child is likely to be taller as an adult than will be a child with a poor diet, infectious diseases, or inadequate health care.

In some cases, ethnicity plays a role in adult height, but studies on immigrant families have shown that moving to a country with better access to nutritious food, healthcare, and employment opportunities can have a substantial influence on the height of the next generation; this suggests that some differences in height between ethnicities are explained by non-genetic factors.

Heredity and Growth

Molecular biologist Chao-Qiang Lai of the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University conducted a study on height variation and its factors.

About 60 to 80 percent of the difference in height between individuals is determined by genetic factors, whereas 20 to 40 percent can be attributed to environmental effects, mainly nutrition.

Human height is a quantitative, or metric, trait, and is controlled by multiple genes and environmental factors. Many studies have estimated the heritability of human height. Often, these studies determine heritability by estimating the degree of resemblance between relatives. One can separate genetic effect from environmental effects by correlating genetic similarity between relatives with their similarity in height. To accurately measure how genetically similar relatives are, we have to get the number of genetic markers they share. For example, Peter M. Visscher of the Queensland Institute of Medical Research in Australia recently reported that the heritability of height is 80 percent, based on 3,375 pairs of Australian twins and siblings.

Other studies have shown height heritability among whites to be even higher than 80 percent.

Because different ethnic populations have different genetic backgrounds and live in different environments, however, height heritability can vary from one population to another, and even from men to women. In Asian populations, the heritability of height is much lower than 80 percent.

Such diversities in heritability are mainly due to the different genetic background of ethnic groups and the distinct environments (climates, dietary habits and lifestyle) they experience.

Heritability allows us to examine how genetics directly impact an individual's height. It can also be used to directly measure or predict an individual’s height when parent’s heights are known. It can also be used to predict an individual's height if the parents' heights are known. Of course, these predictions only reflect the mean expected height of someone since the actual observed height may be different.

Nutrition also affects someone’s growth pattern and inclination to its height. The most important nutrient for final height is protein in childhood. Minerals, in particular calcium, and vitamins A and D also influence height. Because of this, malnutrition in childhood is detrimental to height. In general, boys and girls reach their growth spurt just before adulthood Thus, adequate nutrition before puberty is crucial for height.

In addition, although diseases of childhood can inhibit ultimate stature, human growth hormone treatments can remedy such growth defects. Height accelerated by such treatment or special supplements, however, cannot be predicted based on heritability. There are two reasons: first, heritability has not been estimated in a growth hormone-treated population. Second, genes and growth hormones can interact synergistically to affect height, i.e., their effects may not be simply adding to each other but could be multiplying the ultimate effect.

The question remains, however, why different populations of a similar genetic background might have a differing heritability. The answer is, of course, through environmental effects. When a given environment maximizes the genetic potential of a population for a given trait, this population tends to have a higher heritability for that trait, and vice versa. In developed countries, nutrition for childhood development is strong, which maximizes the genetic potential for height assuming no selection or new mutations.  In contrast, in developing countries, nutrition deficits lead to a lower heritability. Improved nutrition elsewhere may have similar benefits in terms of stature.

With regards to nutritional factors, heights and weights certain parents were recorded and studied on a research published by the Australian and New Zealand Journal of Obstetrics and Gynecology.

It showed that paternal height had a significant influence on birth-weight while paternal body mass index (Quetelets Index) had no significant effect otherwise. Depending upon mother's height, the average effect of father's height (ranging from 165 cm to 184 cm) on birth-weight was up to 152 g, with a greater effect where the mother was taller (up to 235 g) and a lesser effect where the mother was shorter. The significance of these findings lies more with the need to consider this effect as an important variable in statistical analysis involving birth-weight than in its immediate obstetrical implications.

These various factors contribute largely to the growth of an individual. However, the inheritance of a person’s height affects greatly on the genetic makeup of a person which predetermines other physical changes at birth as well.



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