Friday, February 24, 2012

What does the DNA blood test tell us?

Androgen Receptor with KD At least a couple of times a year someone will write and question the accuracy of the DNA blood test for Kennedy’s Disease. This normally happens because a man has identified many of the symptoms he has are also related to Kennedy’s Disease (KD).

It is my understanding that the DNA test is 99+% accurate. Yes, that still leaves less than one percent available for error. Of course, there is the possibility that a person is ‘borderline’ KD. That means his CAG repeats are 34-39. It is also my understanding that borderline cases can exhibit some of the symptoms, but not all of them. The progression is also not as evident.

The two DNA tests that I had showed a scale similar to the following:
  • 0-33 = Normal
  • 34-39 = Borderline
  • 40 and above = Kennedy’s Disease (Spinal Bulbar Muscular Atrophy or SBMA)
So, borderline could be diagnosed as normal by some doctors and also explain why a patient experiences some of the symptoms.

In a study conducted a few years ago, it was reported that the higher the CAG repeat count the earlier the onset meaning the progression is also more apparent over time. I happen to be on the higher end with a 53. I have known others with counts in the low 40s that did not exhibit any noticeable symptoms until the late 50s or 60s. (Boy would that have been nice)

Wikipedia defines these type disorders as Trinucleotide repeat disorders (also known as trinucleotide repeat expansion disorders, triplet repeat expansion disorders or codon reiteration disorders) are a set of genetic disorders caused by trinucleotide repeat expansion, a kind of mutation where trinucleotide repeats in certain genes exceeding the normal, stable, threshold, which differs per gene. The mutation is a subset of unstable microsatellite repeats that occur throughout all genomic sequences. If the repeat is present in a healthy gene, adynamic mutation may increase the repeat count and result in a defective gene.

Wikipedia also explains Kennedy’s Disease as: SBMA is caused by expansion of a CAG repeat in the first exon of the androgen receptor gene (trinucleotide repeats). The CAG repeat encodes a polyglutamine tract in the androgen receptor protein. The greater the expansion of the CAG repeat, the earlier the disease onset and more severe the disease manifestations.

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