Mitochondrial disease is one of the orphan diseases - an ailment that has been ignored by the medical and pharmaceutical industries because of its rarity. There is no money to be made from finding a cure for it.
Governments also allocate little resources to patients with rare diseases as can be seen in the lack of funding for equipment to diagnose mitochondrial disease in Hong Kong.
"Are the lives of rare disease patients less valuable than those with common diseases?" said Christina Hellmann, chairman of the Joshua Hellmann Foundation for Orphan Disease which advocates the rights of rare disease patients.
She set up the foundation in memory of her son, Joshua, who died at 15 in 2007 of a mitochondrial disease called Melas Syndrome, which affects the brain, nervous system and muscles.
The foundation funds tests for suspected cases and has a network of experts providing support to patients and families.
There are between 6,000 and 8,000 types of rare diseases in the world.
In Hong Kong, there is not enough information on the prevalence of rare diseases to generate meaningful estimates.
The term "rare disease" is defined differently from country to country.
In general, a disease is considered rare if it affects up to one in 2,000 people.
A Hong Kong mother, whose three-year-old son has Pelizaeus-Merzbacher disease, researched online for potential treatments for the central nervous system disorder that paralysed him.
She was told her son's case was the only one in Hong Kong.
She found that two treatments are undergoing clinical trials overseas.
She hoped to try them on her son, but was turned down by public hospital doctors before finding one willing to consider it.
"One of the doctors told me, 'People won't conduct a study for a single case like you.' I said, 'A single case is still a human'," said the mother who identified herself as Shirley. "I understand they have their difficulties, but as a mother I felt so helpless."