Managing genetic defects in newborns is challenging for a few reasons, especially when it comes to problems with the metabolism of chemical compounds within cells. There are numerous possible congenital defects, because there are so many biochemical reactions, each requiring specific enzymes (chemical compounds that move biochemical reactions) that are encoded by genes. This means that there are thousands of potential points where inadequacy or dysfunction of just one enzyme can lead to disease. Mutation of any particular gene is unlikely, which means that most genetic diseases are quite rare. However, with 20,000-30,000 functional genes in human genome, the chances of something being wrong somewhere are fairly high, so the chances of being born with some kind of defect are significant, but traditionally newborns have been screened only for a handful of conditions deemed to present the greatest risk.
Currently, medicine depends strongly on genetic assessment and counseling of couples that may carry serious genetic diseases, and on prenatal testing with ultrasound, maternal blood tests, and –in mothers deemed to be high risk—tests of amniotic fluid or placental tissue (chorionic villus sampling). There is plenty of variation in policy, based on a need to balance risk with funding resources. For instance, California requires that all newborns are screened for sickle cell disease, while other jurisdictions approach this genetic blood condition by screening mothers and fathers for sickle cell trait –since having the trait means that one is a carrier of the sickle cell gene. Sickle cell screening is encouraged, particularly for African Americans, and for others with ancestry in places where the sickle cell gene is common. With cystic fibrosis, the highest risk is among Caucasians, but the American Congress of Obstetricians and Gynecologists encourages screening all parents for the cystic fibrosis gene. Similarly, Tay-Sachs disease is notorious for its relatively high incidence among Ashkenazi Jews, where testing is thus a high priority. But Tay-Sachs also strikes French Canadians and several other groups and people usually don’t know their entire genetic history going back more than a couple of generations.
With metabolic conditions, either some key biochemical is not made, or something accumulates, because an enzyme needed to remove it is not produced. Often the health effects manifest very gradually, so they are not seen in the newborn, but they show after weeks or months. There are thousands of genetic conditions in this category; though each one is rare, together they affect a lot of people. By the time such a condition is recognized, there could be irreversible damage to organs, but until recently it was not practical to test for so many conditions. Current genetic technology, however, allows for sequencing of a newborn’s full genome. Within minutes, physicians can know about conditions that normally would take many months to discover, often after the onset of irreversible damage. As for what do with the knowledge, in some cases, a high-tech intervention like gene therapy may be the only answer. However, with many rare metabolic disorders, the answer could be a simple as adding or limiting a particular nutrient on the first day of the child’s life.