The latest report to come from the Bedlington Terrier Health Group in the UK says that the other gene mutations have been identified and all that is holding back research for the definitive test is funding. They recommend to continue using the existing DNA test and to biopsy when possible.
The veterinarian that I use recommends not to neuter before 18 months to ensure correct muscular and skeletal development. Sometimes new owners decide, for various reasons, that they can't wait this long but I strongly suggest leaving it as long as possible.
The latest reports on neutering male to calm them down has shown that it can actually make them timid and therefore more of a handful, discuss neutering with your breeder and your vet to ensure that you are making the right decision for your dog.