Definition
By definition, small stature, also called short stature, is present when the body length or height is below the 3rd percentile of the growth curve. This means that at least 97% of the peers within the general population have a higher body height. For example, if a child is on the 2nd percentile, 98% of children of the same age are taller and 2% are shorter than that child. For adults, once growth is complete, only height is important, regardless of age. At present, the limits of short stature for adults are 150 cm for men and 140 cm for women.
When does one start to speak of dwarfism?
By definition, one speaks of dwarfism when growth occurs below the third percentile. In adults one speaks of a body length below 150 cm. In many cases the cause is familial or constitutional, but in some cases dwarfism is a sign of a chronic, possibly genetic disease. It is important that population-specific reference values for growth are used for the diagnosis. For example, the averages for longitudinal growth of a child born in Canada are different from those of a child born and raised in the Netherlands.
Causes
The causes of dwarfism are very diverse. The most common is, however, familial dwarfism, in which there is no growth disorder. The child’s parents are small, so it is to be expected that the conceived child will be small compared to the general population.
However, growth must be regular and proportionate, i.e. the ratio of body to limbs etc. must be within the normal range. The second most common cause is constitutional growth retardation.
This is characterized by a slower growth rate and especially by a delayed onset of puberty. The growth phase is prolonged, so that the genetically determined target size determined by the parents can be reached. Often, the parents are already aware of a delayed onset of puberty.
Much rarer are hormone deficiencies, e.g. hypothyroidism, reduced production of growth hormone, or chronic diseases. Among the chronic diseases are especially those that make it difficult to absorb nutrients, e.g. chronic inflammatory intestinal diseases or gluten-induced coeliac disease. In addition, a wide variety of genetic diseases can also lead to reduced body size.
These can be inherited by the parents, even if they are not affected by them, or they can also occur anew. In addition, malnutrition, neglect and abuse can also lead to reduced growth. As already mentioned, the height of the child is largely determined by the height of the parents.
By means of the parental height a target height for the child can be calculated, whereby the final height of the child is nevertheless subject to certain deviations from this calculated one. Through this the familial dwarfism comes about, which per se does not represent an illness. The following formula is used to estimate the final height: (height father + height mother +13 cm (for boys) or -13 cm (for girls)2.
On the other hand, genetic diseases can be passed on to the children. In this case, the inheritance path of the disease plays a role and determines the probability of the child falling ill and thus becoming small. This varies greatly from disease to disease and can be assessed by a specialist in human genetics.
There are various genetic syndromes that can cause dwarfism. Achondroplasia, the most common skeletal disease in which the ossification of cartilage and thus bone growth is disturbed, is very well known. This disease is inherited autosomal-dominantly, but in the majority of cases is based on a new mutation, i.e. the parents were neither ill nor carriers of the genetic change.
In this disease, the expected body length is less than 130 cm, with the trunk reaching a normal length and primarily the limbs being too short because the tubular bones do not develop sufficiently. The head appears disproportionately large. Another disease that, depending on its degree of severity, can lead to dwarfism is the so-called vitreous bone disease (osteogenesis imperfecta).In this disease, the production of collagen, which is important for bone formation and stability, is disturbed. Depending on the severity of the disease, this leads to very brittle bones and disproportionate small growth. The inheritance of this disease depends on the type, although the different types differ in their severity.
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