What does the DNA blood test tell us?

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)

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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.