Tania Clarence, 42, will face court after her three-year-old twin sons, Ben and Max, and four year-old daughter Olivia were found dead at their home in New Malden, south-west London, on Tuesday night.
Their father, Gary, who works as a director at City bank Investec, was reportedly away in the family’s native South Africa with the couple’s eight-year-old daughter when the deaths occurred.
Yesterday a friend told a South African website that the three dead children were suffering from spinal muscular atrophy (SMA) – a life-limiting genetic illness.
The inherited disease, which is also known as floppy baby syndrome, leaves children with little or no control of their movements.
The friend said: “They [Tania and Gary] did not go and have babies knowing they were giving them a genetic disease. She’s been slammed for having three kids with SMA.
“They had the one child, their second child, who was young, only a few months old, when she fell pregnant [with the twins]. It was not planned, but they felt they could cope.
“While she was pregnant, the second child was diagnosed as having SMA. The twins were then born premature and they stayed in hospital for a long time. She came home with three kids severely disabled.
“Everything was regulated, everything they ate diarised. I bet Tania had not had a decent night’s sleep in a few years.”
The friend said the three children needed feeding by tubes and, while the couple employed a carer and home help, they did not have round-the-clock assistance.
The friend added: “They tried to have a normal family life in the evening, by not having a house full of carers. Tania’s borne the brunt of it. Gary is a businessman and had to travel.
“Everybody who met her could not but be compassionate. Everybody complains about their kids but at least they’re healthy. It just puts your life into perspective.”
A spokesman for the family told a South African newspaper that Mr Clarence was in “absolute shock” at the tragedy.
Lloyd Marshall said that, after the four-year-old was diagnosed with the condition, it was “50-50” as to whether the twins would have it. “Unfortunately, they did as well,” he said.
He added: “Gary is in absolutely a state of shock – the whole family is.
“He never would have left the UK if he’d known his wife would be left really battling.
“Most of the family are on their way to the UK.”
Mr Clarence’s family, including his mother Anne and sister Derri Phillips are understood to have flown to the UK to support him.
Post-mortem examinations were held yesterday at Great Ormond Street Hospital, Scotland Yard said.