The transition from childhood to adulthood can be frightening for persons with autism.
"It can be a very scary and anxious time. For adults, after special education, they may not be working. They and their families are at a loss,'' says Mr Marcel Semaun, head of adult autism services at St Andrew's Autism Centre.
"They face many challenges. For example, if they do not understand what money is, how would they know how to buy lunch?"
Autism is a complex developmental disorder that includes impairments in social interaction and communication skills. The disorder covers a large spectrum of symptoms and levels of impairment. There are no national figures for autism.
Experts agree that there are more resources and services for children with autism, compared with adults.
"The intervention and support services for adults with autism are definitely less extensive than those for children. This is the same situation worldwide, not just in Singapore. Many parents have highlighted their worries about the care arrangements for their adult dependents with autism, should they die or become too frail to take care of them," says Dr Wei Ker-Chiah, the head of the Adult Neurodevelopmental Service at the Institute of Mental Health.
Says Ms Denise Phua, president of Autism Resource Centre (Singapore): "The support systems and programmes for children and youths with autism have improved tremendously compared with 10 years ago. There has been an increasing number of early intervention centres and special schools for children and youths with autism.
"In comparison, for adults with moderate to severe autism, for example, there are only three day activity centres in Singapore. There is a need for residential care models for adults with autism with ageing or deceased parents."
For housewife Peng Wei Yan, 48, contemplating a future for her son, Zhen Yu, 21, who has severe autism, is "a problem with no solution".
Although he was able to recite a Tang dynasty poem at the age of two, Zhen Yu was diagnosed with autism at about three years old. He needs someone to perform daily tasks for him such as brushing his teeth and showering.
Madam Peng, whose engineer husband works in the United Arab Emirates and who has no domestic helper, had faced "different challenges" when Zhen Yu reached maturity.
While he dashed across the road "many times" and jumped onto MRT tracks on two occasions as a child, she no longer has to worry so much about safety issues.
However, from the time he wakes up, she feels "tense", often because of how he might be perceived in public, "where children who exhibit strange behaviour are generally more tolerated than adults".
His behavioural issues include pacing around tirelessly and biting or beating himself. He cannot communicate and sometimes grabs strangers' drinks in public.
Madam Peng, a Singapore citizen who moved here from China 20 years ago, says she and her husband were too "scared" to have a second child after Zhen Yu.
Zhen Yu's future fills her with despair. She has no relatives in Singapore and worries about how a guardian can be found for him.
"As parents, we do our best to look after him, but we hope that the child will leave before we close our eyes," she says, crying as she speaks.
DIAGNOSED ONLY AT 42
Mr Chua Hian Koon says he has been "the odd one out" since secondary school.
"I do not know how to relate to people," says Mr Chua, an assistant specialist in IT at Pathlight School, a special school for children with autism.
"I am 44 years old this year, but I may not be able to fully understand the social implications of my behaviour. For example, until my sister explained it to me, I was not aware that I sometimes infringed on people's private space and that it could be perceived as rude," says Mr Chua, who has a master's degree in business administration and is a member of Mensa, a society for high-IQ individuals.
He says he "did not have friends and no one wanted to work with me in a team" when he was studying at Nanyang Technological University, where he earned a computer engineering degree.
When his mother died suddenly of pneumonia in May 2013, "none of my friends or then-colleagues came to the wake", he recalls.