It’s not uncommon for those nearing retirement to become nervous about their nest egg, concerned it won’t be sufficient. This has led some savers to pursue self-directed IRAs, an individual retirement account that you control with investments of your own choosing. These IRAs are often invested in real estate, private mortgages, precious metals and private company stock. But with the increasing appearance of bitcoin and other cryptocurrencies in these retirement accounts, the Securities and Exchange Commission has issued a new warning.