def hgnc_id(self, hgnc_symbol, build='37'):
        """Query the genes with a hgnc symbol and return the hgnc id

        Args:
            hgnc_symbol(str)
            build(str)

        Returns:
            hgnc_id(int)
        """
        #LOG.debug("Fetching gene %s", hgnc_symbol)
        query = {'hgnc_symbol':hgnc_symbol, 'build':build}
        projection = {'hgnc_id':1, '_id':0}
        res = self.hgnc_collection.find(query, projection)

        if res.count() > 0:
            return res[0]['hgnc_id']
        else:
            return None