def _get_frameshift_start(self, variant_data):
if DBG:<EOL><INDENT>print("<STR_LIT>".format(variant_data.is_frameshift))<EOL>print("<STR_LIT>".format(variant_data.variant_start_aa))<EOL><DEDENT>if variant_data.is_frameshift:<EOL><INDENT>variant_data.frameshift_start = variant_data.variant_start_aa<EOL><DEDENT>return variant_data<EOL>
Get starting position (AA ref index) of the last frameshift
        which affects the rest of the sequence, i.e. not offset by subsequent frameshifts
        :param variant_data: info on each variant
        :type variant_data: attrs
        :return variant data with additional field for AA index (1-based) of the frameshift start
        :rtype attrs