def _add_exac(self, variant_obj, gemini_variant):
        """Add the gmaf frequency
        
        Args:
            variant_obj (puzzle.models.Variant)
            gemini_variant (GeminiQueryRow)        
        """
        exac = gemini_variant['aaf_exac_all']
        if exac:
            exac = float(exac)
            variant_obj.add_frequency('ExAC', exac)
            logger.debug("Updating ExAC to: {0}".format(
                exac))