Wang Junming may be 25 years old, but he is still the size of a baby.
Mr Wang, from Hunan province in central China, stands just 66cm tall and has the mental age of a small child.
But he has become a social media star after his sister Xiaoling posted videos of her daily life caring for him, growing her following to more than 160,000 people.
In February, Mr Wang was diagnosed with pituitary hormone deficiency, a condition in which the pituitary gland fails to produce the hormones that control growth and metabolism, leaving him trapped in the body of an infant.
Most people with the condition are diagnosed at between six months and three years old, when treatment can begin early enough to allow normal growth into adulthood.
After noticing his condition as a baby, Mr Wang’s parents took him to a hospital in the provincial capital, Changsha, where he was given medication.
But with a monthly income of just 3,000 yuan (£332) from his father’s bricklaying work, the family could not afford to keep up his treatment. This meant he never grew larger than a small child.
Deng Chao, an endocrinologist at the Second Xiangya Hospital of Central South University in Changsha, took on Mr Wang’s case following his diagnosis this year.
He determined that the POU1F1 gene – which regulates mammalian development – was abnormal in Mr Wang.
A study carried out in 2021 recorded just 114 cases such as Mr Wang’s worldwide. Many of those people went on to reach normal height and intelligence after receiving proper treatment.
Doctors believe Mr Wang may one day walk unaided and reach a higher IQ
Mr Wang is now receiving regular hormone therapy, but according to Dr Deng, it is too early to predict what effect the treatment might have.
He believes Mr Wang may one day walk unaided and reach a higher IQ, but whether his bones would be strong enough to bear his increasing weight remained unclear.
Since Xiaoling took over his care, Mr Wang has shown signs of mental development and is now able to recognise his sister.
“Fate did not let him grow up properly, but gave me a little man to care about for life,” she told local media.
It is not thought that Mr Wang’s condition will affect his lifespan.