"The goal of personalized medicine is to utilize a person's genetic makeup for appropriate disease diagnosis and treatment...many onlookers with business acumen...seek commercial gains by offering to decipher the genome of individuals for a fee. The fast rate at which these startup companies have become popular gives the public the impression that the science is moving at equal pace. However, that is not true. These personalized medicine companies say they are merely providing 'information' about an individual's health/disease risk. However...there is not yet scientific consensus on the risk factors for more common complex diseases... Yet for a $1000 or more, one can submit a DNA sample to be sequenced by these companies and a report is sent back with a disease risk assessment."
Genetic predisposition to disease is an extremely complex bag and is only clear for very few monogenic diseases - the more genes involved in a disease process the less clear their roles. Commercial companies may say they can tell you your disease risk for, for example, hypertension or heart disease, but they really can't. That information is based on a limited amount of knowledge about a limited number of diseases.
This topic came up quite often when I was doing my dissertation work. My studies involved disease risk assessment based on gene mutations in hypertension- essentially the very thing the genetic testing looks for. The idea was that we had to be careful how to portray the findings because what was true for the majority of a population (i.e. significant risk factor) is not true for every person on an individual level. Risk is simply that, risk. Having a genetic predisposition does not mean one will get the disease, just as not predisposed will not mean a person will not get the disease. Genetics is only one factor in the development of these diseases, with environment (and we're finding out epigenetics) playing a large and significant role in their etiology and severity.
Genetic screening on the limited information we currently have is not valid for polygenic diseases like hypertension, heart disease, cancer, and a number of other complicated disorders people worry about*.