General Information about Cystic Fibrosis 

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.

Cystic Fibrosis is an inherited disorder  A baby can only be born with the disease if both parents carry the abnormal gene. This is what is known as an 'autosomal recessive' inheritance. Normally the mucus in our bodies is thin and slippery and works as a lubricant. In CF, however, the mucus becomes very thick and sticky, blocking the tiny tubes and ducts of various organs. In approximately 90 per cent of patients the ducts in the pancreas are blocked, and so digestive enzymes produced by the pancreas are unable to flow into the digestive tract. Mucus may also block the tiny bronchial tubes in the lungs causing shortness of breath and a chronic cough.

Recurrent respiratory infections, and malabsorption due to pancreatic insufficiency are the major clinical manifestations of the condition.

» Why is it called Cystic Fibrosis?

When the condition was first discovered, it was thought that the main effect was on the pancreas, an organ in the body which produces digestive juices. The pancreas in children with Cystic Fibrosis contains cysts and increased fibrous tissue, hence the term Cystic Fibrosis of the pancreas. It is now realised that the effects on the pancreas are only one aspect of the condition which is commonly termed Cystic Fibrosis or CF.

» How is Cystic Fibrosis diagnosed?

In New Zealand 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 New Zealand. 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.

» Is Cystic Fibrosis inherited?

Yes, it 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.

The most common mutation causing Cystic Fibrosis is called dF508, and it accounts for between 50-80 percent of all cases of the disease. However researchers have now identified more than 600 other mutations in the CF gene responsible for the disease. Most individuals with Cystic Fibrosis in New Zealand have at least one copy of the dF508 mutation.

» How common is Cystic Fibrosis?

Cystic Fibrosis occurs in peoples of Caucasian origin, but it is rare in Africans, Asians and Polynesians. In New Zealand, it is estimated that about 1 in 25 of the Caucasian population will be a carrier of the abnormal gene, and therefore about 1 in 625 marriages will be between two Cystic Fibrosis carriers. Of all births in New Zealand, 1 in 3000 to 1 in 3,500 infants born will have Cystic Fibrosis. Currently there are more than 400 children and adults with Cystic Fibrosis in New Zealand.

» Can carriers be identified?

Carriers have no features of Cystic Fibrosis and are usually healthy individuals. Being a parent of a child with Cystic Fibrosis was the usual way that carriers of the abnormal CF gene were identified. It is now possible to test for carriers of Cystic Fibrosis. This is particularly advised for close relatives in a family where a person with Cystic Fibrosis has already been identified. In New Zealand genetic services are limited, and are based in large hospitals (see neonatal diagnosis). They or your paediatrician can, however, arrange for the necessary blood tests to be performed.

» Are all children similarly affected?

No, there is a great variation in the effects of Cystic Fibrosis. A few children have adequate digestive juices to digest normal food, but most have to take a special enzyme preparation to aid their digestion. Some children have a persistent cough while others suffer from very few chest infections. Even in one family, one affected child can be troubled much more than another. The reason for this variability is another unknown factor about the condition. Sometimes it is possible to trace the variability in the features of Cystic Fibrosis to the type of mutation causing the disease. A small number of mutations are known to be associated with nearly normal pancreatic function. Sometimes these people also seem to have milder chest disease.