Bad blood between two brothers turned into a family tragedy when the mentally ill younger sibling stabbed his older brother to death in the bedroom they shared, a day after the pair exchanged angry words.

Yesterday, Ng Yao Wei, 23, was handed a seven-year jail term after he pleaded guilty to a charge of culpable homicide.

After Ng was sentenced in a courtroom packed with family and friends, his 87-year-old grandmother told him she would pray for him. "Whatever food they give you, just eat, so that you will be healthy," she said in Hokkien.

Ng's parents, Mr Ng Soon Guan, 64, and Madam Gan Chai Min, 55, appeared distraught. They declined to comment when approached by reporters.

Ng's lawyer Josephus Tan said in court earlier that Ng's parents regretted not being able to protect the brothers from each other and not having discovered their younger son's depression earlier.

"The real victims are the parents," he said. "They have lost one son and, today, they are here to see the other one get sentenced."

Ng was a 21-year-old Singapore Polytechnic student on April 13 last year when he stabbed 26-year-old graphic designer Ng Yao Cheng to death at the Windermere condominium in Choa Chu Kang, where they lived with their parents, eldest brother and domestic helper.

The accused called the police at about 11pm to report a murder on the night of April 13.

Paramedics arrived 10 minutes later to find the victim with multiple knife wounds on his neck and body.

Ng was arrested at the scene. He was charged with murder two days later at Changi General Hospital, where he was treated for injuries.

The charge was later reduced to culpable homicide as Ng was assessed to be suffering from major depressive disorder, which reduced his mental responsibility for the killing.

Yesterday, the High Court heard that the two brothers had an acrimonious relationship and would often quarrel over trivial matters.

On the evening before the incident, two friends of the accused went to his home to play computer games. The older Mr Ng became agitated over the noise they were making and shouted at his brother. In response, Ng called his older brother "a dog" in Mandarin. Their father intervened before the two came to blows.

In the middle of the night, Ng took a knife from the kitchen and hid it under his pillow.

The following night, Ng confronted his older brother for embarrassing him in front of his friends. Angry words were exchanged. When Ng called his brother "an a***hole", the older man lunged at him.

The younger man stepped back, reached for the knife and repeatedly stabbed his brother with the weapon, which had a 20cm blade.

On hearing the commotion, their mother and domestic helper went into the room. The domestic helper took the knife to the kitchen while their mother tried to stem the bleeding on the older Mr Ng with a towel.

An autopsy found that the victim suffered 22 stab wounds.

Yesterday, Ng's lawyer, Mr Tan, asked for a jail term of not more than seven years. He argued that his client, a timid and quiet individual, had been subjected to longstanding physical and verbal abuse by his older brother since he was young.

As they shared a room, his client had no choice but to suffer in silence, he added.

The older brother had also made death threats towards Ng, resulting in the accused hiding the knife under his pillow, said Mr Tan.

Their parents agreed that the older brother was "a hot-tempered and unreasonable individual" who had differences with all his immediate family members but especially with Ng, said the lawyer.

In November 2014, Ng walked into the Institute of Mental Health to seek help but kept it from his family.

Deputy Public Prosecutor Ma Hanfeng sought seven to 10 years' jail, to ensure that the accused is sufficiently treated before his release back into society.

The maximum punishment for culpable homicide is life imprisonment and caning, or jail of up to 20 years and a fine or caning.