LIFE FEATURES:The deterioration of Caoimh was frighteningly rapid, writes Adrienne Murphyin the first of a two-part series about coping with her son's autism.

Around this time last year, my son Caoimh (pronounced "keeev") received his first diagnosis of autism. He was two years and two months old at the time.

In educated hindsight, I believe that glimmers of Caoimh's autism were always there, but its manifestation became dramatically and progressively more intense when he hit about 20 months old. This puts his "disorder" into the category of "late-onset" autism, whereby children appear to be developing normally, until the autism really grabs hold some time after 18 months.

I have a memory that I cherish from the time before Caoimh pulled the shutters down on the world and retreated deeply and almost unreachably into his own mind.

We were at a children's Christmas party. About 20 very small kids were charging around with "bubble bursters" made from sausage-shaped balloons, joyously popping the thousands of bubbles that were pouring from these really cool bubble machines.

A shy child, Caoimh was standing on my knee looking on, needing to gear himself up before he could join in the fun. His cue was spotting his four-year-old brother, Fiach, in the melee. Wielding his bubble burster, he rushed to join him. I remember feeling so happy watching my two little boys dashing around bursting bubbles; it was one of those times when you give thanks for your children's health and think really, there's no greater blessing.

Caoimh was 18 months old at the bubble party. By the age of 22 months, the autism that I did not yet have a name for had so devoured him that he had neither the awareness nor the skills any more to be able to engage in this kind of group play. By the time of his second birthday celebrations - which he shared with Fiach, who turned five the same week - all Caoimh could do was stay in my arms crying, sheltering in confused terror from the activities in his home.

His deterioration, when it began in earnest, was frighteningly rapid. At the creche - which he'd been attending in the mornings since he was 14 months old - biting other kids became a big problem. It's normal for young toddlers to play around as opposed to with each other, but it's not normal for them to be profoundly afraid of each other, as Caoimh was, to the point where he'd often lash out at any who came near him.

His childminders at the creche did their best to get Caoimh to engage and partake, but he became increasingly withdrawn, spending all morning on his own, not playing, not really doing anything but walking round in circles, refusing to eat, resisting nearly everything that took him away from his own inner focus.

I used to pick Caoimh up from the creche at lunchtime after collecting Fiach from his Montessori around the corner. For the first six months that he was there, when Caoimh saw us arriving to get him, he'd rush smiling toward Fiach and throw his arms around him, glad to see his brother again after their morning apart.

But when Caoimh was around 20 months old, Fiach started to complain sadly that his brother never hugged him any more. At first I didn't pay much attention, but then I saw that it was true. Within a matter of weeks, Caoimh entirely stopped showing any affection toward his brother. In fact, all interaction with Fiach dried up - no more sword and shooting games, no more chasing, no more hiding together from the adults, no more squabbling.

I think Fiach knew that something was seriously going wrong for Caoimh at least a month before his dad and I had begun to acknowledge it. Perhaps this is because he's a similar height, and could observe more easily how Caoimh's eye-contact - which was so penetrating as a baby - was rapidly disappearing. Sometimes his eyes became so glazed over and unfocused they were almost zombie-like.

Meanwhile, behaviourally, Caoimh was getting more and more out of control. Most toddlers can be wilful and have tantrums, but Caoimh was extreme in his single-mindedness, in what I viewed at the time as his stubbornness and absolute unwillingness to divert from his own plans or co-operate in the daily business of eating, washing, getting dressed and going places.

Any kind of constraint became anathema to Caoimh. We could no longer get him into the car seat, his buggy or even his nappy or clothes without resorting to man-handling him with our superior strength. He spent increasing amounts of time screaming and was incredibly destructive, constantly throwing anything he could reach to the floor and trying to bite anyone who attempted to thwart his plans. He had no sense of danger, and in public places would either go into meltdown or attempt to run away. Simple outings such as trips to the playground with my friends and their children became insurmountably difficult, and I felt my daily life with him becoming increasingly limited and isolating.

Yet as a baby, Caoimh had been remarkably quiet and contented. My friends at the mother and baby yoga class that I attended would be amazed at how my infant - lying calmly gazing up at me from a cushion on the floor - would let me have a whole hour of stretching without fussing to be picked up.

What we didn't know at the time was that behind Caoimh's lack of striving for involvement in the outside world - which is the norm in babies and can be so demanding - was the shadowy internal focus of a nascent autistic mind.

While, by his second birthday, we'd accepted that Caoimh was turning out to be a child who was ultra-sensitive and "challenging" (to use the PC word for difficult), we still had no inkling that he was a child with special needs, and certainly not a "severe mental disability" such as autism. That was a shock that we were on an inexorable collision course with as the developmental gap between Caoimh and his toddler peers grew ever wider.

And nowhere was Caoimh's developmental delay more pronounced than in the area of language and communication.

Our first son, Fiach, had begun speaking at a remarkably young age. I remember him pointing with excited rapture at a clothesline when he was only 10 months old, engaging me directly and saying, "This! This!". As a person who loves words, I took great delight in observing Fiach's vocabulary expand with such rapid ease, and every night before I went to sleep I counted in satisfaction all the words that he knew, until they became too many to enumerate.

While Caoimh began walking at 12 months just like his brother, his language was always way behind. He was a quiet baby, doing very little of the classic babbling, rarely smiling and never pointing. By the time he was 18 months old, he used only - and then very infrequently - a small handful of words: "doggy", "fish", "door", "there". I remember feeling relieved when I heard him say "mammy" once when he was trying to get back into the house from the garden. I cling to this memory, because this was the first and last time that Caoimh used my name. By the time he was two, the few words that he had disappeared entirely.

We began anxiously seeking out opinions from anyone who might know why Caoimh might not be talking. Many reassured us that lots of children don't really start talking till they're three, and that it was nothing to worry about yet. But not only did Caoimh not talk, he didn't listen either. Most of the time he didn't even react to his own name. We began fearing deafness - a classic parental reaction to the onset of autism.

Our baby couldn't communicate non-verbally, either. He didn't know that all he had to do was look at us and indicate if he needed something; instead he would fly into a rage because he had no way of asking. I remember him going as far as setting the table with placemats once rather than come and get me to indicate that he was hungry.

In play Caoimh was way behind, too. Books were almost his sole obsession. He'd spend hours a day flicking through, running about with, hiding and doing strange, almost ritualistic hand movements over, not colourful children's books, but the same handful of adult books. Bizarrely, these were The Prophet by Kahil Gibran, The Time Machine by HG Wells, a book called Science, Mind and the Cosmos and a beautiful copy of Friedrich Nietzche's Thus Spake Zarathustra, which he was especially fanatical about because I rarely let him have it.

I called Caoimh "the peeper" because at meal times he'd sit opposite me with one of these books held up over his face, then repeatedly pull the book down so I could see his eyes before quickly covering them up again, as though giving me a cryptic sign - by the way he was using these particular books to fleetingly reveal himself - that his was a radically different state of consciousness to the norm.

Apart from his bizarre book behaviour, by the age of two Caoimh's "play" consisted of turning around and around in circles (and never suffering from the dizziness this causes in "normal" brains); trying to scribble all over the walls any time he could lay his hands on a pen; walking on his toes; enacting hand rituals; staring at shadows and light as they played across surfaces; and zoning in on some tiny marks and indentations on the walls, around which he'd compulsively drawn circles.

It amazes me now how I had occasionally used the word "autism" for many years, completely in the dark as to what it actually means. I didn't recognise autism because I was under the ignorant illusion that autistic children rocked their bodies and showed no affection. Caoimh never rocked and was always an extraordinarily affectionate and cuddly child, and indeed craved human contact, though was so obsessive about me that no one else would get a look in if I was around (which greatly pained his exceptionally loving and affectionate father).

While I was still unaware of potential autism, my parents had become suspicious, and gently urged me, without saying the word, to bring Caoimh to a paediatrician. Meanwhile they and my sister prepared the safety net of love and support that we would need as over the course of five months, a team of doctors from various fields diagnosed autism, and we fell into the appalling abyss of grief that parents of newly diagnosed autistic children experience as they come to understand just how devastating autism can be. Would our child ever be able to talk? Would he end up sedated and institutionalised by his teenage years because his behaviour was so out of control?

My baby was dying in all but body. I'd stare in agony at him, desperately willing him to come out of his bubble of fear and isolation and confusion, clasping his little head in my hands as though by some psychic surgery I could undo the neurobiological disorder that was taking him away from me.

But I want to reassure frightened parents that there is hope. Because after the most painful and arduous year of our lives, we have managed to catch Caoimh's kite string and begin the long task of reeling him in. And it's working. He's here again, calm and happy and catching up with his peers, despite autism's most hopeless prognoses.

Tomorrow, part two: Adrienne Murphy on the road followed to retrieve Caoimh

If you are worried that your child may have autism, phone the Solas Diagnostic and Assessment Centre through Irish Autism Action (IAA) at 044-9331609 from tomorrow