A former soldier accused of murdering his terminally-ill son told a jury the boy's death was a "mercy killing".
Doctors had said Jacob would not live beyond his 20s
Andrew Wragg, 38, told Lewes Crown Court he and his wife Mary had been in an "impossible and hopeless" situation caring for 10-year-old Jacob.
He said his son did not recognise him when he came back from serving in Iraq.
Mr Wragg, 38, denies murdering Jacob at the family home in Worthing, West Sussex, but admits manslaughter on the grounds of diminished responsibility.
The court heard on Friday Mr Wragg decided to split from his wife in 1998.
He said: "It was not easy because Jacob was terminally-ill.
Andrew Wragg told police his son's death had been a mercy killing
"I was, and always have been, very hands-on with Jacob. I changed his nappies, bathed him and put him to bed. I did all the normal things."
When he came home from working as a bodyguard in the Gulf, Mr Wragg said he felt Jacob had changed, saying "I just noticed things were a lot quieter.
"Jacob's deformities were more pronounced. He was less energetic," he added.
Michael Sayers QC, defending, asked Mr Wragg if he felt Jacob had still been able to recognise him despite having been away from home.
He replied: "No, I don't think he did."
The court heard the defendant smothered Jacob with a pillow in what he described as a "mercy killing".
After learning Jacob had been diagnosed with the rare degenerative disease Hunter Syndrome, the jury was told Mr Wragg resigned from his job, despite being promoted to acting sergeant while in Bosnia.
Mr Wragg also described the "horrific" moment he and his wife were told their unborn son was also a Hunter carrier.
The couple then decided to terminate the seven-and-a-half-month foetus, the court heard,
The trial continues.