Although significant progress has been made over the last 25 years to identify genetic abnormalities associated with congenital myasthenic syndromes (CMS), many patients remain genetically undiagnosed. A report in the inaugural issue of the Journal of Neuromuscular Diseases identifies a gene defect in mitochondria, specifically the citrate carrier SLC25A1, that may underlie deficits in neuromuscular transmission seen in two siblings.
"While mitochondrial gene defects can cause a myriad of neurological disorders including myopathies and neuropathies, these have not been specifically implicated in defects of the neuromuscular junction," says Hanns Lochmller, MD, Professor of Experimental Myology, Institute of Genetic Medicine, MRC Centre for Neuromuscular Diseases, Newcastle University, Newcastle upon Tyne, UK.
Of the 19 genes that have been implicated in CMS, most express proteins involved in neuromuscular synapse development and function. These mutations usually involve post-synaptic proteins. The current study shifts the area of impairment to the presynaptic region.
Investigators conducted genomic analyses of two patients who are brother and sister. The pair was born to healthy parents who were first cousins. "The family history was highly suggestive of autosomal recessive inheritance," notes Dr. Lochmller. Since childhood, the 33-year-old brother had displayed some speech and motor problems that worsened with exercise and improved with rest. He had mild bilateral ptosis (drooping of the eyelid), speech difficulties, and mild learning disabilities. His 19-year-old sister showed delayed development including recurrent falls, fatigable limb weakness, intermittent double vision, and some drooping of facial muscles.
The investigators performed homozygosity mapping and whole exome sequencing to determine the underlying genetic cause of the siblings' condition and successfully identified a homozygous mutation in the SLC25A1 gene. SLC25A1 is a mitochondrial citrate carrier believed to be a key component in many important biological processes, such as fatty acid and sterol biosynthesis, gluconeogenesis, glycolysis, maintenance of chromosome integrity, and regulation of autophagy.
Using electrophysiologic techniques, researchers were able to show clear abnormalities in the neuromuscular junctions of the patients, as evidenced by increased jitter or jitter with blocking of muscle fibers.
Researchers also found evidence that SLC25A1 may be required for normal neuromuscular junction formation by looking at the effects of reduced expression of SLC25A1 in zebrafish embryos. Anatomically, while the muscle fibers appeared normal, presynaptic motor axon terminals were shortened and grew erratically, with no evidence of complete synapse formation. They also saw structural changes in the brain and heart, which mirrored abnormalities seen in humans.
"It is still not clear how deficits in a mitochondrial citrate carrier result in neuromuscular junction defect," comments Dr. Lochmller. However, while mutations in SLC25A1 may prove to only be a rare cause of CMS, he and his co-investigators advise clinicians that should a patient show fatigable weakness, it may be appropriate to test for SLC25A1 mutations and consider screening for cardiac and metabolic defects should these mutations be found.
"We aimed to identify the underlying molecular defect in this family ever since we met them first in clinic more than 20 years ago," adds co-investigator Kate Bushby, MD, Professor of Neuromuscular Genetics, Institute of Genetic Medicine, MRC Centre for Neuromuscular Diseases, Newcastle University. "We are pleased that latest sequencing technology has resolved this long-standing diagnostic puzzle, which helps us in counseling and treating them more effectively."
Congenital myasthenic syndromes (CMS) are a group of inherited neuromuscular disorders characterized by muscle weakness (myasthenia). Typical symptoms include weakness of muscles controlling limbs, as well those involved with control of the eyes, respiration, and movements of the face, head, and neck (due to involvement of the corticobulbar tract). The symptoms are fatigable, meaning that they worsen with repetition, and severity of the deficits can range from mild to severe.
Read this article:
Mitochondrial Mutation Linked to Congenital Myasthenic Syndrome
- IOM not webcast today. Why Not? - November 8th, 2009 [November 8th, 2009]
- National Academies skeptical at Best. - November 8th, 2009 [November 8th, 2009]
- Some Confusion Exists - November 8th, 2009 [November 8th, 2009]
- Why DTC Genomics IS Medicine. - November 8th, 2009 [November 8th, 2009]
- First Mari, Now Linda. Who's next? - November 8th, 2009 [November 8th, 2009]
- Is it true? - November 8th, 2009 [November 8th, 2009]
- Re-Reviewing the National Academies - November 8th, 2009 [November 8th, 2009]
- The problem with nonclinicians....... - November 8th, 2009 [November 8th, 2009]
- Crazy Night of Emails to Government - November 8th, 2009 [November 8th, 2009]
- Adrienne Carlson's Personalized Medicine. - November 8th, 2009 [November 8th, 2009]
- Tell Me, How do you feel now? Sherpa's RX - November 8th, 2009 [November 8th, 2009]
- This Just In. 23andMe to go to GPs. I love my readers!! - November 8th, 2009 [November 8th, 2009]
- Sorry so long away - November 8th, 2009 [November 8th, 2009]
- 2D6 Rears its ugly head..... - November 8th, 2009 [November 8th, 2009]
- Ok, Fine, Back to Plavix - November 8th, 2009 [November 8th, 2009]
- Kaiser a protoype for Collins' Aim - November 8th, 2009 [November 8th, 2009]
- A few months late to the party.... - November 8th, 2009 [November 8th, 2009]
- Stated Another Way....... - November 8th, 2009 [November 8th, 2009]
- Excuse Me? Harvard and Navigenics? WTF? - November 8th, 2009 [November 8th, 2009]
- Follow up to Yesterday's WTF? Harvard, Navi? and Pfizer??? - November 8th, 2009 [November 8th, 2009]
- Did you get your kit? Thanks Dr. Rob from MedCo - November 8th, 2009 [November 8th, 2009]
- Gluco...Wha? Parkinson's Disease and Glucocerebrosidase mutations. - November 8th, 2009 [November 8th, 2009]
- Away and now back, What did I miss???? 23andme layoffs? Selling Genomes for cheap up next! - November 8th, 2009 [November 8th, 2009]
- Change IS Needed. I agree with William, sometimes. - November 8th, 2009 [November 8th, 2009]
- Good Enough Science? Apparently so at 23andme - November 8th, 2009 [November 8th, 2009]
- Long QT Syndrome, location matters - December 13th, 2009 [December 13th, 2009]
- Congratulations Generation Health. Nice pick up! - December 13th, 2009 [December 13th, 2009]
- An argument 23andSerge can't win...23andme but not medicine - December 13th, 2009 [December 13th, 2009]
- Stop. Breathe. Repeat. An analysis of the direction of DTC Genomics Field. - December 13th, 2009 [December 13th, 2009]
- Hey DTC genomics, Stay Private, Stay Alive, Go Public and Die - December 13th, 2009 [December 13th, 2009]
- You can't have it both way. Either scared your genome is sold off or not. - December 13th, 2009 [December 13th, 2009]
- 15 Days Away Gives Time for Perspective. - December 13th, 2009 [December 13th, 2009]
- What about the SACGHS registry? Another missed opportunity? - December 13th, 2009 [December 13th, 2009]
- AJHG is in and my Favorite Muin is in it! But He Is NOT the Father! - December 13th, 2009 [December 13th, 2009]
- Navigenics for 23andMe prices? - December 18th, 2009 [December 18th, 2009]
- Lp(a) Maybe there's something there that wasn't there before? - December 24th, 2009 [December 24th, 2009]
- Another Year, Another Bankruptcy - December 31st, 2009 [December 31st, 2009]
- 5 Technologies going bye bye in this decade? - January 6th, 2010 [January 6th, 2010]
- Hackers, HITECH and HIPAA in DTC Genomics, Oh My! - January 7th, 2010 [January 7th, 2010]
- Personal Genomics Flop.....big Belly Flop! - January 8th, 2010 [January 8th, 2010]
- Gotta Love It. Even the daycare....... - January 11th, 2010 [January 11th, 2010]
- Congratulations Navigenics. You ARE a clinical lab! Uh-Oh... - January 12th, 2010 [January 12th, 2010]
- CETP, Jewish Centenarians and Alzheimers - January 14th, 2010 [January 14th, 2010]
- Enter the "Not" DTC Genomics Rep - January 17th, 2010 [January 17th, 2010]
- Why Dr. Vanier's Navigenics appointment is good for PM - January 22nd, 2010 [January 22nd, 2010]
- Holy Crap! MedCo Follows in CVS footsteps - February 3rd, 2010 [February 3rd, 2010]
- FDA, Warfarin, still not as sexy to me. - February 5th, 2010 [February 5th, 2010]
- Hype, Hype, Hype from a single study. - February 11th, 2010 [February 11th, 2010]
- I love my readers, even Renata M! - February 17th, 2010 [February 17th, 2010]
- How can insurers use DTC genomics to profile? - February 17th, 2010 [February 17th, 2010]
- 9p21.....ahem. Paynter et.al. Smackdown. Again. - February 18th, 2010 [February 18th, 2010]
- Hey! It's Pete Hulick! Are you Going to GET? - February 19th, 2010 [February 19th, 2010]
- I was wrong......AHEM - February 28th, 2010 [February 28th, 2010]
- G2C2, finally a tool for genomic education! - March 2nd, 2010 [March 2nd, 2010]
- Just 4 million? What 23andMe is worth. - March 5th, 2010 [March 5th, 2010]
- What a difference a year makes - March 9th, 2010 [March 9th, 2010]
- ........DTC Genomic Medicine? - March 12th, 2010 [March 12th, 2010]
- The FDA, 2c19 and the ACC - March 13th, 2010 [March 13th, 2010]
- The problem with Comparative Whole Genomics...... - March 13th, 2010 [March 13th, 2010]
- BRCA testing by 23andME is the same as Myriad Genetics. - March 15th, 2010 [March 15th, 2010]
- The Argument Against DTC Genomics Marketing and such - March 16th, 2010 [March 16th, 2010]
- A moment of Clarity. Some DTCG is not bad. - March 18th, 2010 [March 18th, 2010]
- SNPs for breast cancer risk? It Depends. - March 18th, 2010 [March 18th, 2010]
- How can MDVIP use Navigenics Test for Medicine? - March 18th, 2010 [March 18th, 2010]
- Why did P&G invest in Navigenics? - March 23rd, 2010 [March 23rd, 2010]
- PGx in DTCG? Doesn't stand up to Useful testing. - March 25th, 2010 [March 25th, 2010]
- End of Gene Patents? - March 29th, 2010 [March 29th, 2010]
- Sherpa Accepting Chief Medical Officership - April 3rd, 2010 [April 3rd, 2010]
- The Rumors of My Death........ - April 20th, 2010 [April 20th, 2010]
- Happy DNA Day! - April 25th, 2010 [April 25th, 2010]
- 99 USD, DNA day and patient letters - April 25th, 2010 [April 25th, 2010]
- 2C19, Navigenics and Clinical Reality. - May 1st, 2010 [May 1st, 2010]
- Coriell Personalized Medicine Collaborative rising - May 7th, 2010 [May 7th, 2010]
- Personal Genomes in Clinical Care. Quake paper is a waste! - May 11th, 2010 [May 11th, 2010]
- Personal Genomes in Clinical Care. Quake paper Falls Short! - May 13th, 2010 [May 13th, 2010]
- Last post edited by Drew - May 13th, 2010 [May 13th, 2010]
- GateKeeper? FCUK U! - May 13th, 2010 [May 13th, 2010]
- GateKeeper? F! U! - May 15th, 2010 [May 15th, 2010]
- Potential of genomic medicine, LOST - May 19th, 2010 [May 19th, 2010]
- How Bad Can a House Investigation be for DTC Genomics? - May 20th, 2010 [May 20th, 2010]