Restricted growth, sometimes known as dwarfism, is a condition characterised by unusually short height.
There are 2 main types of restricted growth:
As well as being short, some people with restricted growth also have other physical problems, such as bowed legs or an unusually curved spine.
But most people don't have any other serious problems and are able to live a relatively normal life, with a normal life expectancy.
Read more about the symptoms of restricted growth.
The most common cause of PSS is being born to small parents, but it's sometimes the result of the body not producing enough growth hormone.
Certain genetic syndromes, such as Turner syndrome, Noonan syndrome and Prader-Willi syndrome, can also cause PSS.
A rare genetic condition called achondroplasia is the most common cause of DSS.
It causes poor bone growth, resulting in short upper arms and thighs.
It doesn't always run in the family – many children with achondroplasia have parents of normal height.
The Restricted Growth Association UK has more information about achondroplasia and other rare types of restricted growth.
Restricted growth may be diagnosed before a child is born, soon afterwards, or when growth problems become more obvious as they get older.
Growth hormone deficiency is usually diagnosed using growth hormone stimulation tests.
Medicine is injected into a vein or muscle to cause an increase in growth hormone levels in the blood. A lower than normal level indicates a deficiency in growth hormone.
A brain scan will be needed to look at the pituitary gland (which produces growth hormone) if blood tests show low levels of growth hormone.
If one or both parents have a family history of a condition that causes short stature, their baby can be tested for this during pregnancy (prenatal diagnosis).
Read more about screening tests in pregnancy.
Treatment with growth hormone injections may benefit some people with restricted growth and can help a child with the condition grow more than they otherwise would.
In cases of DSS where the legs are particularly short, a leg-lengthening procedure is sometimes used, but there's some uncertainty about its safety and effectiveness.
Read more about treatments for restricted growth.