subset columns from the 1st file using column names in 2nd file

I have two text files: 1st file is a Tab delimited file which looks like this: chrom pos ref alt a1 a2 a3 a4 10 12345 C T aa bb cc dd 10 12345 C T aa bb cc dd 10 12345 C T aa bb cc dd 10 12345 C T aa bb cc dd 10 12345 C T aa bb cc dd 10 12345 C T aa bb cc dd 2nd file looks like this: a1 a4 I want to extract those columns in the 1st file which are present in the 2nd file along with first 4 columns of the first file. So in the above case, the output will look like this: chrom pos ref alt a1 a4 10 12345 C T aa dd 10 12345 C T aa dd 10 12345 C T aa dd 10 12345 C T aa dd 10 12345 C T aa dd 10 12345 C T aa dd I want to do this in shell. How can I do this? I have a bigger file than shown here, so I have many columns in 1st file cut -f 1-4,$(grep -Fwf file2.txt <(head -1 file1.txt)) file1.txt