The IRS recently issued a private letter ruling that part of the cost of genetic testing may be tax deductible as a qualified medical expense if part of the service includes a medical analysis of the results of the genetic test and results in a report that is presented to the taxpayer's health care providers.
A private letter ruling is issued in response to a request from an individual taxpayer for IRS guidance regarding a tax issue. It may not be cited as a precedent by others taxpayers, but is viewed by tax professionals as a good indicator of the IRS thinking on a particular issue.
Find more details in this article from accounting web.