A St. John's man with a neurological disease that will lead to his death is using the illness as his defence against fraud charges that could send him to prison.

Harold Farr, 52, is being tried at provincial court in St. John's for defrauding the Canada Revenue Agency of about $50,000 between 2004 and 2008.

Farr has been diagnosed with Huntington's disease, a genetic disorder that is gradually destroying his brain.

Court has been told that Farr used his supervisory role to reset employees' passwords in CRA's computers, and gain access to unwarranted tax refunds.

In court Thursday, Dr. Hugh Mirolo, a neuropsychiatrist who has been treating Farr for two years, said Huntington's has caused Farr to have a lack of control over his impulses, and that he could not stop himself.

He said Farr, like other patients with the disease, cannot push away a thought once he has had it. As examples, he said Farr purchased hundreds of curling irons and would keep buying dogs.

Mirolo testified that Farr hid his disease because of stigma about his mental health, and that he did not want his daughters to know about his "death sentence."

Mirolo said Huntington's amounts to "an execution over decades" and that "it's like being on death row."

Mirolo said Farr's impulse, aggression and obsession issues are somewhat under control.

The Crown noted that Farr committed the frauds when he was obsessed, lacked control and was peaking, but questioned why Farr cashed the cheques when they arrived weeks later.

Meanwhile, Mirolo also testified that Huntington's typically makes patients aggressive. He said Farr once challenged a much larger car salesman, and could not stop himself.

The trial was to continue Friday.