Gene testing - an opinion article
by Rob Redden, M.D.

Editor's Note:  Rob is a primary care physician who has HSP.  After questions were raised on the HSP email support group by people seeking input about having HSP gene testing done, Rob shared the article below.  Currently, gene testing is only available for the spastin and atlastin forms of HSP.  These two dominant types are the most common forms of HSP, however, researchers indicate there are at least two dozen different types of HSP. 

The diagnosis of HSP is really fairly straightforward. There are only a handful of things that cause the symptoms and findings of HSP and they are all relatively rare.  Among them, HSP is the only one that is inherited through a gene defect. The others can be demonstrated through blood testing. Unlike those others, which can be ruled out through specific testing that is negative, HSP is among the group of conditions described as diagnoses (plural of diagnosis) of exclusion.

This means that (until very recent time) there were no specific tests that could be done in which, if you had the positive test, you had HSP. Even now, with genetic testing available for a couple of types of HSP, that testing still leaves the majority of folks with HSP without available testing to confirm their diagnosis. I believe that researches with interest in HSP are trying to develop such lab tests for as many forms of HSP as they can, as soon as they can. However, in one sense, they are not necessary for the diagnosis, even if they do provide a perhaps comforting absoluteness to the diagnosis.

I did not have the testing done, but a second cousin of mine with HSP did the spastin gene test, paying for it out of pocket because of his own interest, and it turned out negative. That leaves neither one of us with doubt regarding our diagnosis.  We simply know we don't have the spastin gene defect.  As of this point in time that's a big, "So what?"    

HSP causes, primarily, varying degrees of progressively worsening weakness and spasticity in the lower extremities, period. There are other associated symptoms that people may or may not have, but those two are always present. They are associated with findings on physical examination that show a doctor with intact knowledge of the function of the nervous system that there is a disconnect between the brain and the legs.

The diagnosis should be straightforward: a soul shows up at the doctor's office and reports, "I can't walk right.  I'm having a hard time moving my legs. I feel too weak to get up off the floor. I am falling too often (or whatever symptoms they happen to notice). The doctor should ask some pertinent  questions about prior health history, medications being taken, family history, and other associated symptoms the soul may have.  

Then, on examination of the nervous system, they will find varying degrees of muscle weakness, spasticity, hyperreflexia (meaning when they tap on certain areas of your body, your muscles tighten up excessively), clonus (repetitive, rhythmic jerking of your foot, up and down, after it has been forcefully pressed upward at the ankle as a pivot), and possibly a positive Babinski sign (when they forcefully scratch the sole of your foot with the sharp end of the reflex hammer, and instead of curling up, your toes spread out and turn upward). When they test your sensation, it will be for the most part normal, with possibly a minor loss in sense of position of your toes or of vibration in your toes, in some types of HSP.  

Again, if the doctor does his work right and knows what to make of it, he has demonstrated spastic paraparesis and weakness. All the causes are rare, but in our society, and probably most, HSP is the most common cause of it.  If you are able to provide clear family history, that just about clinches the diagnosis. Even if you don't have family history, as is surprisingly commonly the case, HSP is the most likely cause, and it can be confirmed by ruling out a few other oddball conditions with blood tests and perhaps an MRI or two and an electro-myogram (EMG).  If they are all negative, you have HSP.  

I am surprised, and almost aghast, at the experiences of so many who have been misdiagnosed along the way.  Some have been diagnosed with another rare condition called Charcot-Marie-Tooth disease. That is bizarre, as C-M-T is a condition of the peripheral nerves and gives a picture in ways just the opposite of HSP, except in that the affected individual will have weakness and ultimately paralysis. Other people have been diagnosed with things like MS and cerebral palsy, and although at least these are central nervous system disorders, they do not so cleanly, steadily progressively, and specifically affect both lower extremities. The biggest problem with diagnosis is finding a doctor with awareness of this rare condition, who can make himself think out of the limited box he lives in and consider the appropriate diagnosis, instead of trying to make the findings of the interaction fit into one of the common conditions he is accustomed to working with.

HSP is a condition that can be diagnosed without gene testing, and even the fact that many people with HSP will have a negative test does not mean that they do not have HSP. The outcome of the test has, at present, no clinical utility (meaning, finding the test positive or negative cannot change in any useful way the way that your doctor will treat your condition). My understanding is that there are at least fifteen recognized defects, so far, and there will be more, so having tests to identify two of those cannot be considered a useful part of confirming or disproving the diagnosis of HSP. You remark that it would give you "some sort of feeling of knowing for sure if it comes back positive," but the likelihood of that happening is fairly small, the test is very expensive, and it leaves question as to whether you would further, and incorrectly, doubt your diagnosis if the test came back negative.

We simply don't need to know the specific gene defect to know that a person has HSP.  In the hands of a doctor who is aware of HSP and knows what
he is doing, it is readily diagnosable.  As of this time (and we all hope this will change in the future), knowing your specific gene type offers no special benefit to you in terms of your care or your function.

I will state the following frankly: if you have a test that offers no benefit to your medical care, and your insurance company is meant to cover care for your health, but you want that expensive test, anyway, simply for some potential peace of mind that the test very well may not offer anyway, you should consider paying for the test, yourself.  I don't see it as appropriate to expect the insurance company to pay for something expensive that is not necessary for diagnosis and that does not offer means to improve your condition. You ask, "Is it because of the money involved and the slim chance of it being identified anyway?," and I would have to say that is a significant part of it, but the bigger part of the issue is that even if you are identified by it, as of this point in time, it makes no difference in your condition, and that fact puts the issues of cost and probability in a particular context that adds more question to the value of the very expensive testing.

Insurance companies are not responsible for providing every test that we would like for purposes of peace of mind. I have patients come in frequently who are nervous that they might have a brain tumor because they have a headache. They want an MRI scan of their head, perhaps. There are even those who have requested an MRI scan of their entire body simply because they wanted to make sure there was nothing wrong with them.  These are similar issues of peace of mind.  MRI scans are ridiculously expensive, but still less expensive than the test for the spastin gene!  

For me, as a doctor, my role is to explain that to patients and to contract with them to work on diagnosing the headache for what it is and to work with them to find an effective course of treatment. This is not because I am in cahoots with the insurance companies but because I recognize that health care is tremendously expensive, and resources should be used wisely, where there is likelihood that their use will result in a true benefit to a persons health. To do every test that might be requested of the population for purposes of their peace of mind would clearly add an overwhelming expense to a system that is already tremendously expensive.  

Beyond that, the simple fact remains apparent that if a soul is not comfortable with their diagnosis or is left uncertain of a diagnosis that can be made with certainty (and I understand this to be true of HSP), that soul needs to consider whether they are working with the right doctor and whether they might do better seeking a doctor who is more comfortable with and aware of HSP to make a more definite diagnosis. Unfortunately, such a doctor is not always easy to find,  but when found, their diagnosis will be much more useful than would the limited testing available for specific gene defects causing HSP.

Home