One of these is INCL, a quickly progressing dementia disease that affects infants and leads to profound intellectual disabilities.
Children affected by it are usually healthy at birth, but their development begins to regress when they are about six months old. Within a couple of years, the children go blind, have epileptic seizures and finally become totally dependent on others. Their life expectancy is 9 to 10 years.
INCL is part of our Finnish disease heritage and it is inherited recessively. If both parents are carriers of the disease gene, each of their children has a 25 percent risk of inheriting two defective genes and getting the disease.
At present, the disease often comes as a surprise to the families, because carriers of the disease gene are completely symptomless themselves and the population is not screened for it, explains Helena Kääriäinen, research professor at THL.
Kääriäinen thinks that the time might finally be ripe for carrier screenings for INCL and similar genetic defects. This could prevent highly severe diseases and the strain that they place on families, the community and health care providers.
Screening the population would also reduce inequality, since these tests are already available from private health care providers, she emphasises.
”Symptoms more severe than Down’s syndrome”
According to Kääriäinen, the cost of gene testing is now low enough that society could afford carrier screening for genetic defects.
Political motivation to arrange screening has been lacking, however, because it could lead to terminations of pregnancies, among other things.
I personally believe that screening should be arranged for diseases that are more severe than Down’s syndrome, which is already screened during pregnancy. It would serve as a point of comparison for ethical discourse, Kääriäinen muses.
If both parents are found to be carriers of the same disease gene, the child’s disease status can be determined by gene testing cells from the placenta and the pregnancy can be terminated if necessary. If the family so wishes, they could also consider artificial insemination and embryo diagnostics. In this way, the birth of severely ill or disabled children could be prevented.
Kääriäinen also sees the flipside of the issue: embryo diagnostics facilitate the birth of healthy children.
She stresses that, without the possibility of embryo diagnostics, carrier parents might not dare to have any children.
Should cancer risk genes be screened as well?
In addition to screening the population for recessively inherited disease genes, it would also be possible to screen susceptibility genes that significantly increase the risk of onset of a disease.
These include, for instance, the risk genes of breast cancer, ovarian cancer and cancer of the large intestine.
If we screened the population for these mutations, we could monitor those people with a higher than average risk of getting cancer. Then we could detect cancer early, which is when treatment is most likely to be successful, Helena Kääriäinen explains.
At present, the immediate family members of known carriers are already being screened for cancer risk genes, as well as people who have cancer that is suspected to be hereditary. Screening could be extended to all people who have cancer or to a whole age group, for example.
The population could also be screened for susceptibility caused by multiple genes, such as susceptibility to quickly developing cancers. The results could, for instance, be used to create a personal mammography plan for each woman.
According to Kääriäinen, the benefits from extending cancer risk gene screening to the healthy population might not be significant enough to be worthwhile, however.
Most cancers develop due to reasons other than hereditary susceptibility, she reminds us.
Research Professor Helena Kääriäinen from THL gave a presentation about carrier screening for genetic defects at the Laboratory Medicine and Exhibition event in October 2018.