So now, a little more on Sequenom (SQNM), the little company I wrote about last week after it had earned a spot in Cabot Top Ten Report several times in recent months by bucking the broad market’s downtrend.

Sequenom started out as designer and manufacturer of genetic analysis systems … and this business is growing.  The company pulled in revenues of $12.9 million from these systems in the second quarter.  But the big story is that Sequenom has developed a test for Down syndrome that is performed earlier than traditional amniocentesis, that is less invasive (it analyzes a sample of the mother’s blood), and that is extremely accurate.

The size of the amniocentesis market, by the way, is approximately $2 billion!  If Sequenom gets a good part of this market by offering a better test, its revenues could go through the roof.

But it’s still performing tests on patients to prove the test’s accuracy. In the first 201 patients, the company’s test correctly identified all 10 cases of Down syndrome, while recording zero false positives.

Last Monday, I wrote, “The stock has been acting extremely well in the last three months, hovering in the low 20s as the market fell apart.  It’s a very promising pattern.  Short-term, however, the biggest factor is tomorrow’s analyst and investor briefing, in which the company might release information that moves the stock.”

And it did, announcing that of the next 219 patients, the company achieved 100% accuracy with no false positives and no false negatives.  Perfect.  Going on, management said the company expects to test between 3,000 and 5,000 samples before launching the test commercially in the middle of 2009.

And the stock soared, climbing from Tuesday’s close of 20.41 to a high of 29.14 on Thursday.

If you bought before the spike, congratulations; you might want to take some profits here.  Other investors will, and that’s one of the factors that will likely hold the stock below 29 for the next few weeks.

But the long-term profit potential argues for keeping most of your investment, and for looking for buying opportunities in the weeks ahead, perhaps on pullbacks toward 24.