Digital Currency Group ("DCG"), the parent of Grayscale Investments, boosts its authorization to buy shares of Grayscale Bitcoin Trust ([[GBTC]] +0.9%) to $750M from its prior authorization of $250M.As of April 30, 2021, DCG purchased $193.5M of GBTC shares.As of April 30, the shares' discount to NAV was ~10%, better than ~19% on April 22, but still a discount. On Dec. 21, 2020, the shares traded at a 40% premium to NAV.The share purchase authorization boost comes as GBTC shares continue to trade at a discount to NAV. Source: YChartsDGC plans to use cash on hand to fund the purchases.GBTC's 375% total return in the past year lags bitcoin's 547% surge during the same time period as seen in chart below.SA contributor Alexander J. Poulos blames competing Canadian bitcoin ETFs and hedge offerings and the expiration of a lock-up period for GBTC's discount to NAV.