Medical Matters: There are some conditions that family doctors very rarely diagnose. Not because GPs are incapable of spotting the unusual, but simply because looking after a stable population of 2,000 patients means you can spend a lifetime without seeing some of the more unusual syndromes.
But we all have our long-shot diagnosis to be proud of. Mine involved a patient who came to see me one Saturday afternoon when I was a trainee.
The young man was complaining of quite severe chest pain that got much worse when he breathed in. Clinical examination suggested a pneumothorax - a sudden deflation of a lung, often due to a "blowout" on its surface. You need a chest X-ray to confirm it, so it was a simple decision to refer him to the local hospital.
I remember thinking that he was tall for his age and had the longest fingers I had ever seen. As I made a note on his medical chart I had a eureka moment. He must have Marfan's syndrome! (Of course, it's not as simple as that. You must try to prove a diagnosis, but a subsequent specialist referral and investigations confirmed my hunch.)
The syndrome is a genetic disorder affecting the connective tissues. These form the glue and scaffolding of the body; in Marfan's they are weaker and less stable than normal. As with my patient, the typical person with the syndrome is very tall and thin, with disproportionately long limbs, fingers and toes. Ankles may be lax and flat feet are also common.
Other features include an abnormally shaped, narrow chest (pectus excavatum), hypermobile joints (double jointedness), a high arched palate and crowded teeth, short-sightedness with a risk of developing a dislocated lens, and heart-valve problems.
People with Marfan's are also at higher risk of a sudden pneumothorax - and a life-threatening split in the aorta, the body's major artery, is an ongoing risk.
Mary O'Driscoll, who is 34, works from home in Mallow, Co Cork, but travels each week for meetings. "It was on one of these days in Dublin that I collapsed at work with the most horrendous chest pain. I was quickly brought to a local hospital, where some blood tests were done, followed by an ECG. It was believed the pain was just a bad attack of reflux.
"I was sent home, but thankfully the following morning a casualty doctor brought me back in to review my test results again and promptly admitted me.
"The following day I had the second attack, which this time lasted nearly six hours. The best way I could describe the pain was a dragging, tearing pain from my chest down to my stomach. Four days later a CT scan showed up my aortic aneurysm. The pain from the previous two attacks had been the aorta dissecting," she recalls.
Mary was immediately transferred to St James's Hospital for emergency surgery to repair the large artery. She has recovered well, although doctors are continuing to monitor a possible problem further down her aorta.
In recognition of the genetic basis of the syndrome her siblings were tested for Marfan's. Mary's brother has subsequently shown signs of a leaking heart valve and a dilated aorta.
The disorder affects at least one in 10,000 people and arises as a new genetic mutation - that is, where there is no family history of the syndrome - in up to 30 per cent of cases. Fibrillin 1 (FBN1) is the gene that mutates. Fibrillin is an important part of elastic connective tissue, which helps explain the physical manifestation of the syndrome.
The genetic screening of suspect cases for the mutation is not routinely available and the diagnosis is made on clinical grounds. Tests such as ultrasound examinations of the heart and large blood vessels are key elements of a patient's assessment.
And just to confuse the issue, FBN1 mutations have been noted in people without obvious manifestations of Marfan's syndrome, suggesting it is possible to have a faulty gene without having the full-blown disease.
The Marfan Syndrome Support Group is meeting at the Harcourt Hotel in Dublin on Saturday at 4 p.m. The meeting will be addressed by Prof Andrew Green of Our Lady's Hospital for Sick Children in Crumlin.
It is also the day the support group launches its website, www.marfan.ie, and an information leaflet. The following week members of the support group will give talks in schools and try to raise funds.
You can e-mail Dr Muiris Houston at mhouston@irish-times.ie. He regrets he cannot answer individual queries