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New Possible SIDS Genes Identified
ScienceDaily is reporting that researchers at the Mayo Clinic have identified two more cardiac genes that could contribute to sudden infant death syndrome (SIDS). From the article: "In the two recent separate studies, researchers examined caveolin-3 (CAV3) and the cardiac ryanodine receptor (RyR2) and found molecular and functional evidence in both to implicate them as SIDS-susceptibility genes. Researchers examined the tissue of 135 unrelated cases of SIDS -- in infants with an average age of 3 months old -- that had been referred to Mayo Clinic's Sudden Death Genomics Laboratory for molecular autopsy. In each study, two of the 135 cases possessed mutations in either CAV3 or RyR2."
Recessive genes survive because you can carry the gene and suffer no side-effects. You will pass it on to half of your children (on average), who will like you, become carriers but show no symptoms. If each carrier has an average 2 children, you can expect that the number of carriers will stay roughly constant from one generation to the next.
For a child to show symptoms, both of their parents must be carriers of the recessive gene, and even then there is only a one-in-four chance of a child receiving two copies of the gene in question.
Fatal genetic diseases can survive in the gene pool indefinitely if the gene that causes it is recessive.
I'll probably be modded down for this...
Yep. It's not that unusual, actually. Physicians and epidemiologists start out with a number of dead people. They look for commonalities: symptoms, age at onset, unusual blood chemistry, etc. If they don't know what the root cause of an ailment is but they see similar patterns across a number of deaths, they coin a name for it. Here, it's Sudden Infant Death Syndrome--SIDS.
The name tells you what happens but doesn't explain why. Saying "I have a runny nose and I've been sneezing a lot" would let me put you in the Sudden Adult Sniffling Syndrome (SASS) group, but it doesn't actually tell me what caused your ailment. It turns out that SASS actually has a number of different causes that ultimately lead to the same outcome. You may be having an allergic reaction to pollen. You might have a rhinovirus infection. Maybe you have a brain tumour. For this particular symptom, we have a lot of ways of evaluating the course of the disease and the status of the patient.
With SIDS it is much more difficult. There may be many factors that make an individual susceptible, some genetic, some environmental, some a combination, some requiring a lot of bad luck.
A comparison might be drawn with ALS (amyotrophic lateral sclerosis, known in the U.S. as Lou Gehrig's disease). In ALS, the motor neurons die off slowly, over the course of months or years. It starts in the periphery of the body and works its way up to the brain. Under the 'umbrella' of ALS, about 10% of cases are classified as 'familial'--that is, a patient is related to other individuals with the disease. Within this category, about 20% of cases are linked to one of several mutations in the gene SOD1 (superoxide dismutase). (One would expect most of the other familial cases to be related to other genes or gene combinations.) So while only about 2% of ALS cases are linked to SOD1 mutations, it is without a doubt a "contributing cause".
~Idarubicin
You're assuming a 'fishing expedition' for any random gene mutation in common, though.
These studies looked specifically at genes that were known to be related to heart problems in adults. CAV3 was recently identified as a genetic cause of long QT syndrome, while RyR2 is linked to catecholaminergic polymorphic ventricular tachycardia (press release).
If these mutations occur at a low baseline rate in the general population, two hits of each may be quite significant. This link indicates that RyR2 mutations are rare in the general population, with a probable incidence of under 1%. (They found no mutations in 200 healthy volunteers having 400 copies of the gene.) I'm not going to dig further for incidence numbers, but I'd bet good money that both RyR2 and CAV3 mutations are rare and that getting two hits of each in a population of 135 is quite unlikely.
~Idarubicin