Discuss theories of causes of Generalized Anxiety Disorder

Our textbook reviews theories of causes of Generalized Anxiety Disorder (GAD). Assuming that each theory reflects the experiences of some patients, it would seem that there are many paths to experiencing GAD. But if patients are coming from such different experiences, should we really consider them all to have the same disorder? For example, should one patient with GABA inactivity and another patient with maladaptive assumptions really be lumped together in the same category?