Cystic Fibrosis is a condition with which some babies are born. In fact, it is present from the moment of conception, that is, from the instant the father's sperm fertilises the mother's egg. It is not caused by any previous illness suffered by one of the parents or by anything that happened during the mother's pregnancy. It is non-contagious and affects a number of organs of the body.

In the National Testing Laboratory has been screening all new-born infants for Cystic Fibrosis since mid-1981. This test was devised by Professor Bob Elliott. It measures the amount of pancreatic enzymes in a baby's blood. This is conveniently done by using the blood spot sample which is routinely taken on all babies on the fifth day of life, and which is used to check for other diseases. This measurement of pancreatic enzyme levels is not a definitive diagnosis, but 'screens' out the babies that are likely to have Cystic Fibrosis. If the level is abnormal another sample from the same blood card will be used to test for the four or five most common mutations causing Cystic Fibrosis in the country. All these babies will then be clinically assessed and have diagnostic tests which will include a sweat test. A blood sample will be taken for a diagnostic mutation analysis. A test for pancreatic insufficiency will also usually be performed. The sweat test involves stimulating a small area of the skin to produce sweat, which is analysed for sodium and chloride (common salt). In Cystic Fibrosis there is an excessive concentration of salt in the sweat.

The sweat test will usually be performed at least twice, and now with the ability to screen for several of the more common CF mutations, it is possible to determine on most occasions that a child does or does not have Cystic Fibrosis. However in about 1-2 percent of cases it is still difficult to be absolutely sure based on these tests alone.

Besides new-born screening, other factors which may lead to further investigation are symptoms of pneumonia, or malabsorption, meconium ileus (obstruction of the bowel in the new-born) and an older brother or sister with the disease

Cystic Fibrosis is inherited - that is, it is passed from the parents to the child. Many of our body features, such as hair colour, colour of our eyes, our height, are inherited, or in other words they are determined by genes passed from the mother and father in the egg and sperm respectively. We all have many millions of genes which are very small particles in the body cells which carry all the information about inherited features. All genes come in pairs, one inherited from each parent. Thus we have a pair associated with the colour of our eyes, another with hair colour.

Both parents of a child with Cystic Fibrosis have an abnormal gene in one of their gene pairs. The parents are called carriers of the genes. This single abnormal gene does not cause them any ill effect. If two carriers procreate, they may pass their abnormal genes on to their children. If each parent passes on the abnormal gene, the child will have two abnormal genes and so have Cystic Fibrosis. There is a one-in-four chance of this occurring. There are two chances in four that the child will receive one abnormal gene and so will be a carrier like the parents. There is also another one-in-four chance that neither parent will pass the abnormal gene to the child and so the child will neither have nor be a carrier of Cystic Fibrosis. These chances apply to each pregnancy, so having an affected child does not alter the risk for the next. The incidence is exactly the same for girls and boys.