An Ann Arbor, Mich., couple have become the first to receive a traditional Fannie Mae-backed mortgage using bitcoin collateral for a downpayment. Joe and Amy, in their early 30s, were ready to buy their first home but had most of their savings invested in bitcoin, and did not want to sell, giving up potential future upside while paying capital gains taxes. They found a mortgage from Coinbase and Better Home & Finance Holding Company, which are offering Fannie Mae-backed mortgages to people who meet all eligibility requirements except the cash downpayment, as their assets are tied up in cryptocurrency rather than traditional savings. “The 30-year fixed mortgage was designed for…