Machado-Joseph Disease/SCA 3
Dave has always known he may possess the gene for Machado Joseph Disease (MJD), the same genetic disease that he has witnessed afflict his dad and paternal grandfather. Also known as spinocerebellar ataxia type 3 (SCA 3), it is a dominant hereditary disease that onsets in middle age. ‘Ataxia’ refers to a lack in muscle control or coordination. SCA 3 is caused by abnormally long repeats in a repeating sequence of DNA code in the ATXN 3 gene. In a normal sequence, the code ‘CAG’ repeats 12-44 times. In someone with SCA 3, this sequence is repeated more than 60 times. This disease manifests as slow a decline in motor function, beginning with balance issues and slurred speech. Over years other symptoms develop, including impaired eye movements and vision, muscle spasms, and mobility declines until the affected individual becomes dependent on a wheelchair. In the case of Dave’s dad, symptoms onset at around age 47, and at 60 he is now wheelchair bound, and living full time in a care facility (though this is in part due to other associated health issues). For more information detailing SCA 3, causation and symptoms please visit https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Machado-Joseph-Disease-Fact-Sheet for a more comprehensive overview.
There is no current treatment or cure for SCA 3, although
recent breakthroughs in gene therapy for similar conditions such as
Huntington’s offer hope that perhaps one will exist in the not too distant
future.
Genetic testing exists for SCA 3, but Dave (now 32) had so
far chosen not to get tested, as he didn’t welcome the idea of anticipating the
symptoms. Understandably, he didn’t want to spend his life worrying each time
he was clumsy whether ‘this was it’, if this was the onset of the disease. Of
course, now that we are looking at having a kid, this changes things. As this
is an autosomal dominant disease, a person is affected even if they inherit the abnormal gene from only one parent, and there is a 50% chance of the affected parent passing it on.
There is also a possibility of the disease onset occurring earlier with each
generation, with symptoms in some cases beginning during childhood. We felt it
was important to make an informed decision when it came to the possibility of
passing this disease on to future generations.
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| MJD/SCA3 TL;DR |
The first step
We made an appointment to see our GP, to discuss our concerns together with
other questions we had relating to thinking about having a baby. Understandably,
they don’t just hand out tests for this sort of thing, so she referred Dave to
a genetic counsellor, with a view to having a test conducted. This referral and
the subsequent genetic testing could be funded under the public health system,
with a potential wait time of 2-3 months for an appointment, and a further 2
months for testing as the genetic counsellors are based in Wellington, and only
visit Nelson every couple of months. Now that the decision had been made
however, Dave was anxious to get the test done. We opted to enquire about funding
the consultation privately to try and move things along a bit faster. At a cost
of $300 for an appointment for the genetic counsellor, and an additional $AU250
for the test, we decided it was worth pushing forward. The genetic counsellor
contacted Dave and kindly agreed to have our consultation via video call, so
that we didn’t have to travel or wait for her next visit to Nelson.
During the call, the genetic counsellor was informative,
eloquent and thoughtful in forming our case and talking us through the testing
process. She had access to Dave’s dad’s medical records including his test
results, and asked Dave some questions relating to how the disease has affected
his family members, particularly his father and grandfather. She also checked
whether Dave was currently experiencing any symptoms himself (thankfully he
isn’t). We discussed why Dave had decided to take the test, and what our
options were should he test positive.
Testing
After discussing the disease, causation, family history and our motivations the genetic counsellor talked us through the testing process. She mailed out a test kit and paperwork with a courier pack pre-addressed for the referral genetic testing laboratory in Australia. The kit consisted of two sterile swabs (like cotton tips) with vials of solution to put them in when the samples were obtained. The sample collection itself was simple; first thing in the morning (so before consuming any food or water, or brushing his teeth which would contaminate/dilute the sample) Dave swabbed the inside of his cheek with each swab before sealing it into the vial of solution. (So not that other thing you were thinking, but there is a story about that for later).
We were initially told the testing would take 3-4 weeks, and
when the results came in the genetic counsellor would contact Dave to set up
another video call to discuss them with us. After a tense wait with no news
Dave emailed on the fifth week, and the genetic counsellor cc’d us in with
correspondence she had after following up with the lab. They explained that the
scientist who had started the test earlier that week had gone on leave
unexpectedly, but we could expect results the following week. We were frustrated
that they seemingly hadn’t even started the test until we followed up on it,
but at least it sounded like we’d have the results soon. The next email said
the entire batch of tests (including ours) had failed. As they investigated why
and started a new test, we were told it would be another week before we
received our results. We were beyond frustrated at this point! Finally, Dave received
an email that the results were finally in, almost eight weeks from when we
submitted the sample for testing. We set up an appointment to talk to the
genetic counsellor that night, who very kindly rearranged her evening to fit us
in.
