For most of her life, Dr Dawn-joy Leong, 51, has been viewed as an oddball.

She could fold origami at three years old and composed a musical play at the age of nine. But while obviously intelligent, she was labelled difficult and spoilt when she had what were perceived as tantrums and could not be consoled.

In school, teachers said she was lazy when she aced English Language but failed English literature, despite studying hard for both subjects.

As a young adult, Dr Leong, the third of four daughters, found it challenging to make out societal norms and expectations. She felt lost trying to figure out what to say and how to behave at parties. The concept of telling white lies to avoid social embarrassment was also bewildering to her as she preferred to be frank and direct.

When she was in her early 40s, she felt suicidal following the death of her father, to whom she had been close, and amid acrimonious, hurtful interactions with people she knew, one of whom called her "crazy".

So, she sought psychiatric help. It was only then, at the age of about 42, that she was diagnosed as being autistic.

"It was a relief. I always knew I was different. I had thought, 'Am I a bad person? But I was not bad. There was nothing wrong with me. I just function differently,'" says Dr Leong, a multidisciplinary artist who worked as a librarian and a pre-school teacher earlier in her career.

After decades of having been mocked by peers, teachers and family members, the catharsis she felt gave her the impetus and energy to pursue further studies - a Master of Philosophy degree in music composition at the University of Hong Kong and, subsequently, a PhD in autism and art at the University of New South Wales in Sydney.

She is working on art pieces that help others understand aspects of her autistic experience for an exhibition in Sydney, which opens in September.

Autism is a complex neurobehavioural condition that includes difficulties in social interaction and communication skills.

Because of the wide range of its symptoms, such as requiring rigid routines and unusually focused interests, this condition is called Autism Spectrum Disorder (ASD). It ranges in severity from a handicap that somewhat limits an otherwise neurotypical or "normal" life, to a profound disability that may require institutional care.

Earlier this month, British writer and mother of four Laura James published a memoir, Odd Girl Out: An Autistic Woman In A Neurotypical World, which recounts her experience of being diagnosed as autistic at age 45.

Children as young as three years old can be diagnosed as autistic, says Dr Lam Chee Meng, principal autism consultant at Autism Resource Centre (Singapore).

Adult diagnoses might come about due to increasing awareness in recent years of Autism Spectrum Disorder - some people may seek diagnosis after recognising certain autistic traits in themselves from reading news reports, he says.

"People with high-functioning autism may also be diagnosed later as they can be successful in what they do and social, emotional and relationship issues surface only later in life," he adds.

"There is also the possibility that autism is attributed to other co- morbidities - such as ADHD (attention deficit hyperactivity disorder), dyslexia and anxiety - resulting in autism being diagnosed later."

A diagnosis is only a beginning, says Dr Lam.

"While a diagnosis can provide signposts for intervention and access to services, what is more important is that the individual with autism knows his strengths and how he can overcome challenges using appropriate strategies," he says.

Indeed, Dr Leong and other autistic persons interviewed by The Sunday Times, all of whom are not married, speak of a clarity in understanding their past struggles after they received their diagnosis as an adult, having passed off for years as non-autistic, neurotypical persons.

Some feel that being autistic is now an essential part of their identity and reject being defined according to the standards of "normal" society.

Dr Leong is keen to dismantle myths about autism. For example, one stereotype of autistic persons is that they lack empathy. For herself, she found it too distressing to study history because of the pain and suffering it described, which ultimately led to her not showing up for her A-level history examination.

As an autistic person, she is also sensitive to sensory issues. In the 1970s, her mother used to take her as a child to a wet market, where chickens were slaughtered. The smells she encountered there led to meltdowns, which she says looked similar to temper tantrums, but were involuntary responses to sensory overload. A child yelling for ice cream, in contrast, can be placated with a popsicle.

Being called "normal" and not seeming autistic are common remarks Dr Leong faces, which she feels is derogatory, however unintended.

"At a job interview, I was told that I had 'very good eye contact' and did not 'appear autistic' - that was supposed to be a compliment.

"However, it is an insult because it meant that behaving non-autistic is something to be applauded, while showing my natural autism is not acceptable," says Dr Leong, who has a blog.

The workplace can be challenging because of possible stigma surrounding autism.

When Eric, who does not want to reveal his full name, suspected he was autistic after reading an online news report on the condition, he sought a confirmatory diagnosis at the age of 18.

After learning of the diagnosis, Eric, 34, says his self-esteem "went through the roof" after years of low self-regard and episodes of bullying in primary and secondary school over his apparently odd behaviour, which he now understands is linked to his condition.

Lacking social skills, he did not know how to talk to his schoolmates who were interested in football and game cards. He was interested only in subjects such as chemistry and cacti. He also had difficulty remembering names and faces.

After graduating from polytechnic with a diploma in logistics engineering and management, he went to several job interviews that ended quickly after he mentioned that he was autistic.

One non-governmental organisation at which he applied for an office job said it did not want to take the "risk" of employing an autistic person, he recalls.

Eric, who blogs about autism at iautistic.com and has written several books about the condition, has been in his current IT job, which he got through a friend's recommendation, for more than four years. It is his fourth job since graduation.

In contrast, Mr Khor Kuan Min, 32, landed himself a job because he was upfront about his diagnosis in his early 20s of Asperger syndrome, which has been described as a neurobiological condition at the higher-functioning end of the autistic spectrum.

After finishing his master's degree in English literature at National University of Singapore, he was determined not to let his condition affect his ability to earn a living. He approached Autism Resource Centre's Employability and Employment Centre, which provides training, job placement and job support services for those with autism.

The centre helped place him in his current job of close to four years as an assistant executive who does research and administrative work at MOH Holdings, the holding company for Singapore's healthcare institutions.

On account of having Asperger syndrome, Mr Khor finds initiating social contact extremely difficult.

Hence, when he started the job, he told his supervisors how he could perform optimally given his condition - such as how he preferred communicating by e-mail instead of having to guess people's social cues and facial expressions, which took up a lot of energy.

Mr Khor says: "This knowledge of why I was different eventually led to my taking pride in who I am. In the past, I would have given anything to be normal, but now, I'm staunchly protective of my identity and my right to the same opportunities as everyone else."

For Ms Husnah, 27, learning more about being autistic has helped her cope with the neurotypical world. She was diagnosed at 23, albeit reluctantly, by a doctor who did not think she was on the autism spectrum. In fact, Ms Husnah, who had been reading up on autism and recognised some of its traits in herself, pushed for this assessment.

Ms Husnah, who declines to be identified in full, has learnt to adapt to being autistic, such as putting on headphones when she anticipates unpleasant noises on the MRT.

Her parents have been supportive as they understand her need for quiet and personal space and that crowds and large family gatherings can be draining on her.

Ms Husnah, who works in IT technical support, says she is not defined by her disability.

"Things started clicking with me as soon as I read up about autism. My reactions, emotions, behaviour and even my thoughts finally made sense to me. I finally understood myself. How many people can say that about themselves at the age of 23?" says Ms Husnah.

Being autistic, she says, is "like how you define ethnicity".

"It's a big part of your identity, but it doesn't engulf you to become your only identity. This is a disability, albeit an invisible one, but I am so much more than that."