Scope of the tests
Unfortunately genetic research has not succeeded in finding an answer to all the questions that can arise. There are a number of possibilities:
- different genetic defects can give rise to identical or very similar clinical pictures. As a result it is not easy to find out exactly what the genetic defect is;
- also the same genetic disorder can cause different symptoms in different individuals, and the disorder can also develop in a different way. This is often the case in so-called metabolic diseases, and in mitochondrial disorders;
- the symptoms do not always correspond to a known genetic defect. Scientists sometimes spend many years looking for various 'suspect' genes, which is like looking for the proverbial needle in a haystack;
- although it is theoretically possible to test all genes, this is not feasible in practice. For example, there are a number of rare inherited disorders for which the determinant gene is in fact known, but a routine DNA test cannot be carried out. That is because developing a test requires so much time and money that it is not feasible to do it for a single individual.
However the new technique of genome wide analysis may now offer promising possibililities in this respect.