As a sufferer of OCD (particularly pure-O), I believe there needs to be a genetic predisposition to OCD in order for trauma to trigger OCD in someone. So there is no distinction between trauma-induced OCD and non-trauma-induced OCD other than the trigger.

Change genetic predisposition into neural predisposition because that necessarily is the mediating factor between genetic predisposition and OCD.

This neural disposition may result from other events or conditions than merely genetic predisposition, e.g., a problematic pregnancy or birth. And the genetic predisposition may only result in a neural predisposition under unfavorable developmental conditions during youth. Both genetic predisposition and neural predisposition may be different for different types of OCD, e.g., incompleteness-related OCD vs. fear-of-harm related OCD vs. mixed types.

The neural predisposition may vary in degree among individuals. If it is strong, the development of OCD may be almost unavoidable; if it is mild, it needs prolonged unfavorable developmental and/or living conditions to unfold its destructive impact.

An isolated traumatic experience will probably be not enough to trigger the development of OCD, even if there is a relatively strong predisposition. The trauma will need the additional contribution of prolonged unfavorable living circumstances to result in OCD, of all disorders. And there will be plenty of OCDs that have not been preceded by a trauma.

OCD is similar to many other psychiatric disorders in that the manifestation of the 'symptoms' are incredibly heterogeneous. For example there are 636,120 different ways to have post traumatic stress disorder based on current psychiatric diagnosis, and there are so many ways that psychotic symptoms can be combined that it makes it nonsensical to consider these as discrete disorders. Therefore it is incredibly unlikely that there is a simple genetic explanation for these complex and multi-faceted disorders.

Mark's answer is very helpful and fascinating that there might be 636,120 ways to develop PTSD..... I guess is my question is two fold... Is there any research related to origian question: do you need to have a genetic disposition to develop OCD whether related to PTSD or not.....and second does it make any difference in terms of treatment what the origins of the symptoms of OCD are.... I am not an expert in this field of OCD... but in terms of PTSD... my work has reallly indicated that each person is an individual and although there are certain concepts to keep in mind with these injuries... such as help them deal with the present versus the past ( Judith Herman's work 1992), each individual responds differently and that needs to be your focus.... thoughts

Personally I think relegating environmental factors to mere triggers for the 'genetic' effect is merely an attempt to try and keep afloat the sinking ship of biological psychiatry. The search for the genetic basis of any psychiatric disorder has been an overwhelming failure to date, while the environmental models of psychopathology (and indeed psychometric models that demonstrate the nonsense of psychiatric diagnoses) have been very successful - see the work of Richard Bentall, Jim van Os and John Read.

Traumatic experiences have a negative effect on mind functioning which creates anomalies in the biological brain and physiology. This may be termed as epigenetic, and is causing altered genetic expression. Therefore there doesn't have to be a a genetic predisposition for OCD or any other psychopathological state such as depression, PTSD, Schizophrenia,etc. There is an abundance of contemporary scientific literature that suggests this. Therefore, the genetic basis of psychopathology is tenuous.