[advance online publication in the journal Brain, 6/2015]
Mutations in more than 70 distinct loci and more than 50 mutated gene products have been identified in patients with hereditary spastic paraplegias, a diverse group of neurological disorders characterized predominantly, but not exclusively, by progressive lower limb spasticity and weakness resulting from distal degeneration of corticospinal tract axons. Mutations in the SPAST (previously known as SPG4) gene that encodes the microtubule-severing protein called spastin, are the most common cause of the disease. The aetiology of the disease is poorly understood, but partial loss of microtubule-severing activity resulting from inactivating mutations in one SPAST allele is the most postulated explanation. Microtubule severing is important for regulating various aspects of the micro- tubule array, including microtubule number, length, and mobility. In addition, higher numbers of dynamic plus-ends of microtubules, resulting from microtubule-severing events, may play a role in endosomal tubulation and fission. Even so, there is growing evidence that decreased severing of microtubules does not fully explain HSP-SPG4. The presence of two translation initiation codons in SPAST allows synthesis of two spastin isoforms: a full-length isoform called M1 and a slightly shorter isoform called M87. M87 is more abundant in both neuronal and non-neuronal tissues. Studies on rodents suggest that M1 is only readily detected in adult spinal cord, which is where nerve degeneration mainly occurs in humans with HSP-SPG4. M1, due to its hydrophobic N-terminal domain not shared by M87, may insert into endoplasmic reticulum membrane, and together with reticulons, atlastin and REEP1, may play a role in the morphogenesis of this organelle. Some mutated spastins may act in dominant-negative fashion to lower microtubule-severing activity, but others have detrimental effects on neurons without further lowering microtubule severing. The observed adverse effects on microtubule dynamics, axonal transport, endoplasmic reticulum, and endosomal trafficking are likely caused not only by diminished severing of microtubules, but also by neurotoxicity of mutant spastin proteins, chiefly M1. Some large deletions in SPAST might also affect the function of adjacent genes, further complicating the aetiology of the disease.
We are excited that Giving Tuesday is coming up soon. It is a once a year event and is a perfect accent to the holiday season. Unbeknownst to the commercial world, the holiday season is not about who gets more for me, me, me. It is about that special feeling you get when you know you have really helped out someone you care about or love. It is knowing that the dollar you give today is going to blossom into a million dollars worth of relief from suffering for the people with HSP and PLS. Welcome to Giving Tuesday and we Thank You for your consideration.
When Clinical Trials begin in 2017 it may require as many people as possible for the Clinical Trial to be effective. If you have HSP or PLS, please add your information to our data base so we can keep you informed. We are missing a lot people's email address, so if you just want to add your email address. just enter your name, address and email and we'll add it. That way, we will be able to reach you quickly at a lower cost. Your privacy is very important to us. We will never share any of your information with any individual or company without your permission.
We operate out of the strength of our community, caring friends and sponsors. Your help makes a difference! Our volunteers give many hours of their time annually, and the opportunities to help are as varied as our helpers. Read more.