Growth hormone deficiency as a cause for short stature in children
Growth hormone deficiency (GHD) can cause a slow rate or flattening of growth in children, and also changes in muscle mass, cholesterol levels, and bone strength in adults. We spoke to Dr Penelope Coates, Clinical Director of Chemical Pathology at SA Pathology, to discuss this condition, which affects around one in 4,000 to 10,000 children.
“Most importantly, growth hormone is essential for an increase in height in children; however, it is also responsible for other things such as muscle mass and even energy. Growth hormone is produced in a gland called the pituitary gland which is situated below the brain, just behind the bridge of the nose. A deficiency can develop if there is a problem with the pituitary gland, for example if there is a benign tumour in the gland. Failure of growth in children can also occur for other reasons, including nutritional problems, significant other illnesses, or even significant stress to a child. GHD can also be caused by a physical injury or through infections, but these causes are less likely.
“Signs of GHD all depend on the age at which it occurs. If a newborn baby has problems with the development of the pituitary gland, or has a benign tumour, then the sign might be low blood sugar. Therefore in a small baby, low blood sugar levels combined with anything ranging from difficulty feeding to even seizures, would suggest GHD. In older children, the obvious sign is failure to grow in height. Children are normally carefully monitored by their parents; growth charts are usually available in the handbook provided when you have a baby, so you should be able to see if your child is growing normally. These are the two most common signs,” said Dr Coates.
Growth hormone is secreted from the pituitary gland in a pulsatile manner, meaning in a burst-like or episodic way, rather than constantly. Therefore, as levels of growth hormone vary throughout the day, and peak and dip at different times, measuring the level of growth hormone at one single point in time does not always assist with the diagnosis.
“One of the least helpful tests is an isolated growth hormone test. If you see one single growth hormone level and it is well within the normal range for the age then that excludes a deficiency, but a low level doesn’t mean that the child has GHD, because of the pulsatile nature of the hormone. Typically, there will be some form of stimulation test which might be done by a paediatric endocrinologist; this is a specialist test which is typically done when it is suspected that you’re producing too little growth hormone.
“One of the most common stimulation tests employs a dose of arginine, an amino acid which is administered to the child to stimulate growth hormone production. Growth hormone levels would then be monitored by taking blood samples at timed intervals to monitor the effects. Exercise may also be done because growth hormone normally increases during exercise. There is a second hormone called insulin-like growth factor which is made in the liver in response to growth hormone and has levels which are much steadier during the day. In children, levels of both of these hormones are much higher than in adults; low levels of insulin-like growth factor could be suggestive of GHD, but that test is not the only thing that needs to be done.” said Dr Coates.
If the patient shows signs and symptoms of GHD and their growth hormone levels stay lower than they should during a stimulation test, then it is likely that there is GHD. Likewise, if GH levels do not increase when a person exercises vigorously, then they may have GHD and further testing would be required.
“One of the things that can confuse the issue is if the child is very overweight, as this can blunt the response to provocative tests. Typically, more than one test will be needed if people are going to think about treating a child with GHD.
“In addition, it is important to note that when we are interpreting a single level of growth hormone or insulin-like growth factor, then it needs to be compared to children of the same age. This is because there are two periods of very rapid growth: one in very early infancy, and one in teenage years during the teenage growth spurt. Therefore, it is very important to compare the child to an appropriate reference group, which is one of the things that the pathologist will do. The pathologist needs to have that information and have a good database of what normal results are at different ages,” said Dr Coates.
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This article appeared in the December 2018 Edition of ePathWay which is an online magazine produced by the Royal College of Pathologists of Australasia (http://www.rcpa.edu.au/Library/Publications/ePathway).
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