However, no home visit or call to paramedics was made by either doctor and Mrs Morse said she was told to give Ryan soluble paracetamol and bring him in on the Monday.
Mrs Morse said she decided to stay with Ryan in the living room that night but woke at around 4am to find he was not breathing.
Addison's disease is a rare disorder of the adrenal glands.
Heather's gun is secretly hidden in a doll, kept closely in Sarah's hands.
Sarah is convinced that she drowned her sister, a fact found to not be true.
Dr Yvette Cloette, who examined Ryan's body after he was admitted to hospital said in a statement read to the inquest, she formed the opinion he might have died from Addison's disease.
She said: 'I believe Ryan's death was preventable.'Addison's is a condition that once recognised can be treated to prevent it being fatal.'She added that it was easier to put everything together retrospectively than it would have been for a GP treating an acute illness.
The inquest heard Ryan returned to the surgery on November 7, when he was seen by Dr Rudling who took Ryan's blood, but said two weeks later that the results only showed a slight reduction in white blood cells.