I started rabble rousing about the fallacies of psychiatric classifications (diagnoses, nosologies) about eight years ago. Five years ago I went public, since that time I've labeled 29 posts as "diagnostic definition" related  including my most recent rant...
... We're due for another DSM edition, but I doubt that will be any better.
The good news is that in the last 8 years it's become clear to every researcher that all of the common neurospychiatric conditions, from "ADHD" to "ODD" to "Autism" to "Aspergers" to "Bipolar disorder" to "Schizophrenia" are very rough categorizations of thousands of different "phenotypes" (where a phenotype is the end-result of the interaction between genes and environment) that are themselves dynamic over the lifetime of the brain. (Even after adolescence, we see major changes in schizophrenic symptoms between 20 and 50.
Over the last 3 years we've seen that many different combinations of diverse gene variants, combinations, "malfunctions" and prenatal genetic express modification can produce superficially similar clinical presentations that we squeeze into the garbage bins of "mental retardation", schizophrenia, and "autism spectrum disorder". Most surprisingly, many brains with extraordinary genetic disorders appear normal.
This classification problem isn't simply an annoyance for researchers and industrial ontologists. It has important legal, educational, financial and, yes, clinical implications. The legal, educational and financial implications are large but outside the scope of this post. Suffice to say there is a reason that the diagnosis of "autism" has exploded while the diagnosis of "mental retardation/DCD" has shrunk (clinically speaking both diagnoses are about equally useless)...
... In a recent article in the American Journal of Psychiatry, a Swedish team of researchers led by Paul Lichtenstein studied 7,982 twin pairs. They found a heritability of 80% for autism spectrum disorders, but also found substantial sharing of genetic risk factors among autism, attention deficit hyperactivity disorder, developmental coordination disorder, tic disorders, and learning disorders.
In another recent article in the American Journal of Psychiatry, Marina Bornovalova and her University of Minnesota colleagues studied 1,069 pairs of 11-year-old twins and their biological parents. They found that parent-child resemblance was accounted for by shared genetic risk factors: in parents, they gave rise to conduct disorder, adult antisocial behavior, alcohol dependence, and drug dependence; in the 11-year-olds these shared factors were manifest as attention deficit hyperactivity disorder, conduct disorder, and oppositional-defiant disorder. (Strikingly, attention deficit disorder co-occurs in both the autism spectrum cluster and disruptive disorder cluster.)
... , DSM disorders do not breed true. What is transmitted across generations is not discrete DSM categories but, perhaps, complex patterns of risk that may manifest as one or more DSM disorders within a related cluster. Second, instead of long-term stability, symptom patterns often change over the life course, producing not only multiple co-occurring diagnoses but also different diagnoses at different times of life.
Please read the above excerpt. I tear up looking at it.
This is progress! This is what Osler did for medicine in around 1900 when he tore down the outworn and deceptive strictures of 19th century medicine. He had to throw out the old ideas to move medicine forward. At long, long, last psychiatry, and neurology, are ready to be refactored.
The battle may rage for years, but the war is done. It's just mopping up now.
Now we can move forward.
 Greene's Explosive Child, by the way, led the way in 2005 by setting aside non-useful ICD-9 and DSM classifications in favor of a label that tied symptoms to effective management.