Three tracks can be cited to explain:
- The first is linked to all the sometimes serious diseases these children can have. During them, such as pneumonia for example, growth is slowed by the fact that all the body resources are mobilized to fight against the disease and certain metabolic functions are affected
- The second concerns the problems for swallowing and more generally is the result of the physical effort provided by the person with AT for feeding herself.
- The latter is related to low rates of production of a hormone, IGF1
Efforts to feed oneself
When too much effort is needed to bring food or drinks to the mouth and / or swallowing, eating may not be a pleasure any more but a constraint. From there, the child with ataxia telangiectasia may diminish, unintentionally but gradually, the food quantity it absorbs and thus creating a deficit in a number of essential nutrients for growth and physical fitness .
It is therefore important to observe children's behavior regarding food and take into account any difficulty.
But this may not be sufficient to ensure the child for normal growth. It can then be considered using a feeding gastric tube (see (cf Eating) ), which can be very effective but, like any solution, does not have only advantages and should be discussed with the doctor.
IGF 1 (insulin-like growth factor 1)
IGF1 is produced by the liver and stimulated by GH. The insulin has also an influence on its operation. Like it, IGF1 stimulates the arrival of nutrients in muscle, which has the effect of increasing protein synthesis and muscle mass (anabolic effect sought by some athletes).
For the growth function, it is the mediator of growth hormone (GH). In other words, when the pituitary gland releases GH , it tells the liver to produce IGF-1 which, from binding to its receptors on the surface of cells, will allow them to accept nutrients to reproduce, to grow or renew.
It is now certain that IGF1 is associated with the child in the process of growth plate cartilage of long bones and muscle development. But recent studies show that it is also involved in the growth and maintenance of brain cells and nervous system, particularly in myelination (the manufacture of insulation located around the communication cells of the nervous system, like plastic around electrical cables).
It was also shown that a continuous deficit of cell repair actions, as can be found in AT, had a direct impact on the IGF1 hormone and causes accelerated aging of cells, therefore an overall accelerated aging of the individual, as described in AT.
ATM and IGF1
The optimal functioning of all hormones depends not only on their rates, that is to say their production, but also on the quality of their receptors. If they are not functional, the hormone can not act.
In Ataxia Telangiectasia, low or no ATM protein leads to a double IGF1 deficiency:
- In children with AT is found a low level of IGF1, but also of its main carrier protein, IGFBP-3, which allows it to not be eliminated by the kidneys and can act longer. However, it has been shown in AT mice that direct injection of growth hormone (GH) is not leading to the normally expected production of IGF1 by the liver, as has been explained in the preceding paragraph. This proves the role of ATM in this process. We can conclude: ATM default = production default of IGF1
- According to researchers, the expression of IGF1 receptor (IGF1-R) that allow the cell to absorb nutrients is dependent on the ATM protein in the process of responding to DNA damage during radiation or assault (see ATM: DNA controller ). This function being deficient in ataxia telangiectasia, one can assume that the IGF1-R receptors are equally, either in number or quality, or simply because they are not enabled. Conclusion: ATM default = defects IGF1 receptor
Finally, IGF1 and ATM are also linked to other processes, such as the regulation of cholesterol and fatty acid synthesis (in connection with another protein, AMPK-?). This could explain why most children with AT have a low body mass index.
In conclusion, the trio ATM, IGF1 and GH (growth hormone) could not only explain the stunting of children with AT, but also partly the body degradation linked to ataxia telangiectasia (see Body controlo).
It must be borne in mind that while some children with AT have a slow growth, they develop harmoniously and, again, this does not affect their ability nor their intellectual dévellopement.
But growth retardation, in any child, is a primarily source of complex and may require psychological support (see Psychologist).