from typing import List


def concat_MSA(msa_files) -> List[str]:
    """
    Concatenate MSA files and return lines
    """
    lines = []
    for msa_file in msa_files:
        with open(msa_file, 'r') as f:
            lines += [line.strip() for line in f.readlines() if line[0] != '\x00']
    return lines