from typing import List


def count_unique_genes(gene_list1: List[str],
                       gene_list2: List[str]) -> int:
    """
    Given:
        gene_list: list of string
    Return:
        number of unique genes appear in both list.
    """
    intersect = set(gene_list1).intersection(set(gene_list2))
    return len(intersect)