Cystic fibrosis (CF) will soon be added to the growing list of disorders included in the expanded Ontario Newborn Screening panel. Ontario is the second jurisdiction in Canada to perform testing for CF, following the success of the Calgary Newborn CF Screen Pilot Project. “We are very excited to be adding CF to the panel of diseases for which all babies in Ontario are screened. We are confident that this will make a big difference in the lives of children affected by CF and their families,” says Dr. Pranesh Chakraborty, Geneticist and laboratory Director of the Ontario Newborn Screening Program at the Children’s Hospital of Eastern Ontario (CHEO).
Cystic Fibrosis CF is an inherited disease affecting primarily the lungs and digestive system. The body produces thick mucus that clogs the lungs and heightens susceptibility to infection. The mucus also obstructs the pancreas, preventing enzymes from being released into the stomach to help digestion.
CF affects approximately one in every 3,600 children born in Canada and approximately 40 babies born in Ontario each year. Most babies with CF don’t show symptoms right away and are not identified until after six months of age, or much later. Symptoms tend to be non-specific, including recurrent cough, abdominal pain, loose stools and failure to thrive, often delaying diagnosis.
Treatment for CF includes chest physiotherapy and inhaled medications to improve lung function. Artificial enzymes taken orally at mealtimes also help combat malnutrition. Thanks to improved treatment in recent years, the predicted average life expectancy for individuals with CF is now in the mid-30s. With newborn screening, babies with CF should be identified by 6 weeks of age, permitting immediate treatment and optimum physical growth of the child, thus reducing later health complications.
In the genes CF is caused by a defective pair of cystic fibrosis transmembrane conductance regulator genes (CFTR genes), which encode a protein that regulates the transport of salts across cell membranes. A double dose of a defective CFTR gene is responsible for the production of thick mucus.
For a child to have CF, he or she must inherit a defective CFTR gene from each parent. This is known as recessive inheritance. Approximately 1 in 30 Ontarians “carries” a defective copy of the CFTR gene. Carriers are usually unaware that they have one defective copy of the CF gene since they do not have the disease, or any of its symptoms.
How the screen works Newborn screening for CF will start with the analysis of a substance, called immuoreactive trypsinogen (IRT), in the blood spot routinely obtained in the first week of life from a simple heel prick. Babies with CF usually have pancreatic obstruction, resulting in abnormally high levels of IRT. The IRT level alone may be high enough to trigger a “screen positive.” A baby with an increased IRT and one or two CF mutations will also be considered “screen positive” for CF. Confirmation of the diagnosis involves a combination of sweat chloride testing and repeat genetic testing.
It is important for parents to understand that a positive screen is not the same as a diagnosis. “Screen positive” does not mean that a baby has CF, rather that there is an increased risk and follow-up is required. “Communicating newborn screen positive results to families is a balance of ensuring they understand the potential seriousness of the results while not instilling panic. When screen results are presented sensitively, families are able to process this often unexpected information,” explains Shelley Kennedy, Genetic Counsellor.
Reaching out across the province Newborn screening includes many steps, from the health-care provider who performs the heel prick and completes the blood dot card, to the laboratory processing the samples, and the network of health-care providers who locate the screen-positive babies and arrange follow-up. Newborn screening follow-up centres across Ontario are being established to facilitate confirmatory testing for infants and information provision for families. These centres will work alongside existing CF clinics that coordinate ongoing care for adults and children with CF.
Newborn screening: The big picture Newborn screening in Ontario has seen a dramatic overhaul in the past few years. In 2005, the program shifted from a Public Health Laboratory to a dedicated Newborn Screening Program based at CHEO in Ottawa. “The Program currently screens every baby born in Ontario for 27 diseases. Expanding the program from its original panel of two diseases involved a tremendous effort and commitment from many people at CHEO and across the province. Similar expansions are occurring in provinces across Canada and we’re hopeful that they will be adding CF to their programs as well,” notes Dr. Chakraborty.
The philosophy remains unchanged; screening attempts to identify treatable disorders in neonates that, if undetected, would lead to mental retardation or have life-threatening consequences. The benefits of early detection and treatment will soon extend to CF, improving the prognosis of children born with this complex disease.