An MRI study doesn't provide any conclusive evidence that BPD could be a biologically based disorder rather than a personality disorder.
Personally, while I have no doubt about the existence of the personality disorder, I agree with pidge and generally think it's become a convenient and trendy catch-all to justify adult erratic a$$holes, much like the all-pervasive ADHD for kids. Great strides have definitely been made in learning more about the actual disorder and the options for treatment are growing all the time, which is great. I just find it odd that so many people are getting "diagnosed" with a disorder that apparently most therapists and doctors won't tell their patients they have???