The new research also quashes the suggestion that Hitler had Jewish ancestry.

Popular World War II songs often mocked Hitler's anatomy but lacked any scientific basis.

The findings by an international team of scientists and historians now appear to confirm longstanding suspicions around his sexual development.

"No one has ever really been able to explain why Hitler was so uncomfortable around women throughout his life, or why he probably never entered into intimate relations with women," said Alex Kay of the University of Potsdam.

"But now we know that he had Kallmann Syndrome, this could be the answer we've been looking for," he said.

The research findings are featured in a new documentary, "Hitler's DNA: Blueprint of a Dictator", due to be broadcast on Saturday.

The testing found a "high likelihood" that Hitler had Kallmann Syndrome and "very high" scores -- in the top one percent -- for a predisposition to autism, schizophrenia and biopolar disorder, programme makers Blink Films said.

The research team stressed that such conditions, however, could not explain or excuse Hitler's warmongering or racist policies.

Over 50 million people are estimated to have died in World War II, including six million Jews were who were systematically murdered.

The testing was made possible after researchers obtained a sample of Hitler's blood from a piece of material taken from the sofa on which he shot himself. 

Kallmann Syndrome often results in "low testosterone levels, undescended testicles and can result in a micropenis", Blink Films said.

The DNA results additionally rule out the possibility that Hitler had a Jewish grandfather via his grandmother, who was rumoured to have got pregnant by an employer in whose house she worked.

"Analysis of the DNA debunks this myth by showing that the Y chromosome data matches the DNA of Hitler's male line relative. If he had Jewish ancestry (through an outside relationship), that match wouldn't be there," the production company added.

Geneticist Turi King, known for identifying the remains of medieval king Richard III and who also worked on the project, said Hitler's genes put him in a category of people who were often sent to the gas chambers by the Nazis.

"Hitler's policies are completely around eugenics," said the expert in ancient and forensic DNA at the University of Bath in western England.

"If he had been able to look at his own DNA... he almost certainly would have sent himself," she said.

The two-part documentary is scheduled to begin on the UK's Channel 4 on Saturday.