The delicate-looking young man was compelled to see me by his mother, who sat with him in an outpatient consultation room at the Institute of Mental Health. It soon transpired that she wanted me to "cure" him of his homosexuality - a word she couldn't bring herself to say.
Homosexuality was described as "a pathological deviation of normal sexual development" by the American Psychiatric Association (APA) and listed as a disorder. This is no longer the case. Following the vigorous protests of gay rights activists, the APA in 1973 had its membership vote on the issue of its classification. The outcome was the elimination of homosexuality as a disorder - and that was "the first time in history that a disease was eradicated at the ballot box", quipped psychotherapist and author Gary Greenberg.
Until well into the last century, the prevailing orthodoxy was that a homosexual individual was either depraved and ought to be punished, or was sick and, therefore, in need of treatment.
Mr Alan Turing was a brilliant British mathematician who, in the midst of World War II, figured out the workings of the Enigma, the seemingly unbreakable cipher machine that the German military was using for its communications. Celebrated as a war hero, he was credited to have helped bring the war to an earlier end. But, in 1952, he was convicted on homosexuality charges. To stave off imprison-ment, he subjected himself to chemical castration with female hormones with the intent of suppressing his "unnatural" desires. Whether this led to his suicide a year later remains unanswered.
Currently, there are some therapists (and self-styled therapists) who offer sexual reorientation therapy for gays and lesbians. This sort of therapy, covering a slew of different approaches, aims to change a person's sexual orientation.
Most major mental health organisations have explicitly voiced their disapprobation about the lack of evidence of the effectiveness and expressed disquiet about the possible harmfulness of such therapy. They have also renounced the idea that homosexuality per se was something that could or should be cured or corrected.
In 1991, a neuroscientist named Simon LeVay published in the journal Science his post-mortem brain study of a small group of homosexual and heterosexual men. He reported that a particular region in the anterior hypothalamus - a part of the brain that is long believed to have a role in sexual behaviour - was, on average, more than twice the size in heterosexual men as in homosexual men.
(Prior to that in the 1970s, East German surgeons attempted unsuccessfully to eliminate homosexuality in men by operating on the hypothalamus). LeVay's study heralded many other studies that searched for a biological substrate of homosexuality, including those that examined the effects of sex hormones on foetal development and the genetics of sexual orientation.
So far, there is strong evidence that biological factors do play an important role in the development of sexual orientation, though it is currently not clear to what extent. What is known at this point is that sexual orientation represents a highly complex behavioural trait with multiple determinants, including genetic and hormonal factors interacting with one another.
Stemming from this is the fact that homosexuality (as with heterosexuality) is an inborn characteristic which is involuntary in people and is, therefore, not a matter of choice.
The analogy that is sometimes used for homosexuality in the politics of gay rights is the innate characteristic of one's race. Just as people should not suffer discrimination because of their race, homosexual people should be legally protected against discrimination, and the stigmatisation of homosexuality is hence the equivalent of racism - so goes the argument.
There is also the notion that if science can clearly show homosexuality to be biologically determined and immutable, there will be greater societal acceptance.
But science alone will not enable us to reach a more ecumenical take on the status of homosexuality in our society. The issue is too riven by a cacophonous mix of religion, culture and politics, and too freighted for any calm discussion among the different camps.
The tolerance and acceptance of homosexuality varies from one country to another. In June this year, the US Supreme Court ruled that the Constitution guarantees a right to same-sex marriage, while in Uganda gays have been hunted and killed, and lesbians in South Africa have been subjected to "corrective rape". In Singapore, a same-sex relationship (more precisely, "any act of gross indecency" between men as stated in Section 377A of Singapore's Penal Code) is a criminal offence punishable with imprisonment.
The possibility of becoming a felon didn't stop the young man in my clinic from seeking kinship and acceptance among the gay subculture and community outside his family. He felt the stirring of this same-gender attraction in his pubertal years.
"To reach puberty and find oneself falling in love with members of one's own sex is to experience a mixture of self-discovery and self-disgust that never leaves a human consciousness," wrote Mr Andrew Sullivan, the former editor of The New Republic and who is a Roman Catholic gay. "If the stigma is attached… to the deepest desires of the human heart, then it can eat away at a person's sense of his own dignity with peculiar ferocity. When a young person confronts her sexuality, she is also completely alone…The very people she would most naturally turn to - the family - may be the very people she is most ashamed in front of."
In his autobiography On The Move, the neurologist and writer Oliver Sacks narrated the scene when his mother "with a face of thunder, a face I had never seen before" confronted him over his homosexuality. "You are an abomination…I wish you had never been born," she told him and did not speak to him for several days.
When she did speak, she made no mention of what she had said and never after that, but Mr Sacks felt that things were never the same again - "something had come between us".
Decades later, in his 80s and obviously still hurting, he rationalised: "We are all creatures of our upbringing, our cultures, our times… My mother did not mean to be cruel, to wish me dead…But her words haunted me for much of my life."
In that moment of realisation and in their appalled imagination, these parents perhaps envisage a bleak future where their children would encounter a gauntlet of prejudice and discrimination. Maybe, too, some parents mind very much that they would, henceforth, be seen as parents of a gay child - an identity which they might find shameful and abhorrent.
Most straight parents would want their children to be straight and if things turn out otherwise, their first impulse would be to "get the problem fixed", as with this young man's mother who had sought help from me with such desperate hopefulness. After a long discussion, as they left my clinic, I could not miss the sense of her profound disappointment.
That was years ago and I have not seen them since. In hindsight, I wished I had told the mother that parental reaction to such revelation can significantly influence the young person's self-esteem and irreparably shape his expectations of acceptance or rejection by others outside the family.
There will be some parents who will reject their offspring and continue to feel repulsed; some will insist that their child remain in the closet than to come out and face the external world with its varying shades of homophobia. But some will, with time and habituation, and by dint of parental love, come to tolerate and accept this part of their child.
•The writer is vice-chairman of the medical board (research) at the Institute of Mental Health.