TERF1 and hyperinsulinemic hypoglycemia, familial, 4: It is also noteworthy that while deficiencies in TRF1 or TRF2 appeared similar to those associated with NHEJ deficiency in regard to telomere instability, which presumably occurred via ATM-mediated classic NHEJ (99), the response of cells to IR exposure in the setting of POT1 knockdown differed.