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Worldwide Hotspots of Hereditary ATTR Amyloidosis (ATTRv)

Transthyretin Amyloidosis, or ATTR, is considered a single disease, however the diversity in its clinical presentation is staggering. In this blog, we’ll discuss some of the most common hereditary variants and how the disease manifestation differs around the world in documented hotspots.

Source: Epidemiology, Genetics, and Prognostic Factors (1)

There are two distinct forms of Transthyretin Amyloidosis (ATTR), the hereditary form (ATTRv), and the non-hereditary form (ATTR-wt) commonly referred to as wild-type amyloidosis. Disease manifestation is considered a spectrum involving aspects of cardiomyopathy, neuropathy, or more frequently a mixture of both.

Below we’ll discuss the hereditary form and the various genetic variants and how they differ based on geographical location.

  

WHAT IS TRANSTHYRETIN (TTR)

Transthyretin, also known as prealbumin, is a protein produced primarily in the liver that is responsible for the transport of thyroxine and retinol. Interesting enough, this is how it got its name.

In steady state, the protein circulates primarily as a tetramer (i.e., monomeric form), but unfortunately, its monomeric form is inherently amyloidogenic (prone to breakdown and formation of amyloid aggregates). Couple that with mutations that increase the amyloidogenicity of the protein, these tetramers dissociate into monomers that will misfold, aggregate, and form the insoluble fibrils (“amyloid”) that are resistant to the body’s inherent protective mechanisms like proteolysis. 

 

SPECIFIC TTR PATHOGENIC VARIANTS

As of today, there have been over 145 reported variants related to hereditary transthyretin amyloidosis. Interestingly, these genetic variants have a tendency to cluster in both geographic and ethnic groups around the world. We’ll discuss some of the most prevalent mutations below.

Val122Ile

This is the most common TTR mutation in the United States, with a prevalence of roughly 3.4% in the African American community. The disease is primarily cardiac in nature, typically present when patients are in their 60s. It is thought that this mutation arose from the region of West Africa and has worked its way to the United States over time, where it has become the predominant form. 


Val30Met

This is the most commonly recognized TTR mutation worldwide and the first TTR variant discovered. It is most commonly found in the regions of Portugal, Spain, France, Japan, Sweden, and Brazil. Interestingly, between these regions where this mutation dominates, there is variability in age of onset and parent-of-origin. For example, age of onset was found to be earlier in the Swedish population in comparison to Portugal and Japan. As for the parent-of-origin, it was found that the mother was more likely than the father to pass along the mutation (153 vs. 138), whereas in the French population the father was more likely to pass on the mutation (219 vs. 216), although not by much. The one thing these populations do have in common is this form of the disease is almost exclusively neurologic in nature.

Thr60Ala

This variant is most commonly found in the UK and Irish populations, and is also seen in the Appalachian region of the United States. This variant presents as a mixture of both cardiomyopathy and neuropathy symptoms. It seems to be that in early stages of the disease the neurologic symptoms are most prevalent, but cardiac symptoms present at diagnosis seem to indicate poorer patient outcomes.

Thr119Met

This is arguably the most interesting variant that was investigated in a large study of the Danish population. The presence of this mutation actually confers a protective benefit. When this mutation occurs along with the Val30Met mutation, it has the effect of stabilizing and delaying, even preventing transthyretin amyloidosis.

 

PROGNOSIS

While the prognosis is by no means near perfect, it is improving. There is continued advancement in the field of transthyretin amyloidosis, whether it be improving diagnostic methods, drug development, or a potential cure on the horizon with CRISPR gene-editing technology. Having said that, there continue to be significant barriers to diagnosis. The importance of being an astute clinician to suspect and work up for amyloidosis remains at the forefront of the challenge.

 

CONCLUSION

The geographic nature of this disease plays an important role in identifying and diagnosing amyloidosis. Having an understanding of how the presentation of the disease is heavily related to the patient’s ancestry and location around the world. The hardest part is suspecting amyloidosis, from there don’t forget the value of the diagnostic tools at your disposal, including genetic testing. Use this knowledge to strengthen and guide your suspicions of amyloidosis!

 

Over the upcoming months we’ll post blogs delving deeper into some of these variants, so stay tuned.

Thanks for reading,

Mackenzie

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SOURCES

  1. Obi CA, Mostertz WC, Griffin JM, Judge DP. ATTR Epidemiology, Genetics, and Prognostic Factors. Methodist Debakey Cardiovasc J. 2022 Mar 14;18(2):17-26. doi: 10.14797/mdcvj.1066. PMID: 35414855; PMCID: PMC8932385.

  2. Witteles, R. Unraveling the Lineage: The Genetic Basis of Familial ATTR Cardiomyopathy. Presentation to Heart Failure Society of America. 

  3. Hereditary Amyloidosis Among Portuguese Americans

  4. Cardiomyopathy & Amyloidosis

  5. Peripheral Neuropathy & Amyloidosis

  6. Cardiomyopathy vs. Peripheral Neuropathy

FDA Approved AMVUTTRA for hATTR

Alnylam Announces FDA Approval of AMVUTTRA™ (vutrisiran), an RNAi Therapeutic for the Treatment of the Polyneuropathy of Hereditary Transthyretin-Mediated Amyloidosis in Adults

– First and Only FDA-approved Treatment Demonstrating Reversal in Neuropathy Impairment with Subcutaneous Administration Once Every Three Months

– AMVUTTRA Met Primary and All Secondary Endpoints, with Significant Improvement in Polyneuropathy, Quality of Life and Gait Speed Relative to External Placebo 

– Company Expects to Launch in Early July, with Value-Based Agreements to Accelerate Access 

The FDA approval is based on positive 9-month results from the HELIOS-A Phase 3 study, where AMVUTTRA significantly improved the signs and symptoms of polyneuropathy, with more than 50 percent of patients experiencing halting or reversal of their disease manifestations.

Following yesterday’s U.S. FDA approval, people in the U.S. prescribed AMVUTTRA (vutrisiran) and their families can now enroll in Alnylam Assist, our patient support services program, to receive help accessing this new therapy.    https://bit.ly/3HjOg5Q

PRESS RELEASE

Peripheral Neuropathy & Amyloidosis

Neuropathy, also known as peripheral neuropathy, is a broad term that is used to describe damage to the nerves outside of the brain and spinal cord. There are over 100 types of peripheral neuropathy that can be classified into four categories, with each type having their own symptoms and prognosis. In this article, we’ll discuss the types of peripheral neuropathy and its connection to amyloidosis.

 

Symptoms

One of the challenges with neuropathy is the fact that symptoms can vary significantly based on what nerve is damaged. Additionally, symptoms can develop over the course of months to years (chronic neuropathy) or come on suddenly (acute neuropathy). Some of the most commonly seen symptoms are listed below:

  • Muscle weakness
  • Cramps
  • Muscle twitching
  • Loss of muscle and bone
  • Changes in skin, hair, or nails
  • Numbness
  • Loss of sensation or feeling in body parts
  • Loss of balance or other functions as a side effect of the loss of feeling in the legs, arms, or other body parts
  • Emotional disturbances
  • Sleep disruptions
  • Loss of pain or sensation that can put you at risk, such as not feeling an impending heart attack or limb pain
  • Inability to sweat properly, leading to heat intolerance
  • Loss of bladder control, leading to infection or incontinence
  • Dizziness, lightheadedness, or fainting because of a loss of control over blood pressure
  • Diarrhea, constipation, or incontinence related to nerve damage in the intestines or digestive tract
  • Trouble eating or swallowing
  • Life-threatening symptoms, such as difficulty breathing or irregular heartbeat

 

Types of Neuropathy

  1. Motor Neuropathy → Damage to the motor nerves control how you move.
  2. Sensory Neuropathy → Damage to sensory nerves control what you feel.
  3. Autonomic Nerve Neuropathy → Damage to autonomic nerves that control functions that are involuntary (ie. you do not consciously control).
  4. Combination Neuropathies → Damage to a mix of 2 or 3 of these other types of neuropathies. For example, damage to both sensory and motor nerves would result in sensory-motor neuropathy.

 

Amyloidosis

Peripheral Neuropathy is one of the hallmarks of amyloidosis, often seen in the transthyretin form of amyloidosis (ATTR). ATTR-PN, or transthyretin amyloid polyneuropathy, is a disease where the transthyretin protein becomes unstable and misfolds. This unstable protein (“amyloid”) then deposits in the nerve tissue, resulting in damage to these nerves. While amyloid deposits primarily in the peripheral nerves, it is not uncommon for amyloid deposition in the autonomic nerves as well. 

While peripheral neuropathy is most commonly associated with ATTR amyloidosis, it should be noted that peripheral neuropathy is also seen in 15-35% of patients with AL amyloidosis.

Most importantly, these are the most common and important signs and symptoms to be aware of, in order to diagnose ATTR amyloidosis.

Looking to learn more about peripheral neuropathy in amyloidosis? Check out this wonderful video, where the Amyloidosis Support Group hosts Dr. Chafic Karam to discuss the topic in great depth. https://www.youtube.com/watch?v=9PsSST2gOIg

 

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References:

https://my.clevelandclinic.org/health/diseases/14737-neuropathy

https://www.hopkinsmedicine.org/health/conditions-and-diseases/peripheral-neuropathy

https://www.mayoclinic.org/diseases-conditions/peripheral-neuropathy/symptoms-causes/syc-20352061

https://practicalneurology.com/articles/2021-july-aug/neuromuscular-amyloidosis

https://healthjade.net/familial-amyloidosis/

 

Hereditary Amyloidosis Among Portuguese Americans

According to Alnylam Pharmaceuticals, “Americans of Portuguese descent are disproportionately impacted by hereditary ATTR (hATTR) amyloidosis, a rare, rapidly progressive, and debilitating disease affecting multiple organs and tissues. These individuals have a high prevalence of the V30M variant, which is the most common of the more than 120 gene variants known to be associated with hATTR amyloidosis. The V30M variant is associated with nerve symptoms of numbness, tingling, and burning pain in hands and feet. People of Portuguese descent who develop the disease experience earlier onset symptoms, with 87 percent experiencing symptoms before age 40.

 

Watch this informative news segment featuring Dr. Anthony Geraci, a neurologist who specializes in managing hATTR amyloidosis. He is joined by Julio, who was diagnosed with the disease a few years ago, and his daughter and caregiver Renee. Together they explore the experience of living with this rare, genetic disease.”

The good news is there are FDA-approved treatments and clinical trials which may be helpful; however, the key is to get diagnosed as early as possible. 

CRISPR/Cas9 – Editing the Code of Life

AN UPDATE  …..  WOO HOO!!!

Well, the results of the preclinical studies were presented on June 26, 2021 and it is fantastic news for hereditary ATTR amyloidosis patients!!!

Preclinical studies showed durable knockout of TTR after a single dose. Serial assessments of safety during the first 28 days after infusion in patients revealed few adverse events, and those that did occur were mild in grade. Dose-dependent pharmacodynamic effects were observed. At day 28, the mean reduction from baseline in serum TTR protein concentration was 52% (range, 47 to 56) in the group that received a dose of 0.1 mg per kilogram and was 87% (range, 80 to 96) in the group that received a dose of 0.3 mg per kilogram.

CONCLUSIONS
In a small group of patients with hereditary ATTR amyloidosis with polyneuropathy, administration of NTLA-2001 was associated with only mild adverse events and led to decreases in serum TTR protein concentrations through targeted knockout of TTR. (Funded by Intellia Therapeutics and Regeneron Pharmaceuticals; ClinicalTrials.gov number, NCT04601051. opens in new tab.)

The New England Journal of Medicine
https://www.nejm.org/doi/full/10.1056/NEJMoa2107454


Our original blog post ….

 

The scientific world is abuzz … a Nobel Prize-winning technology called CRISPR/Cas9 can now edit our DNA. This programmable gene-editing technology, which is efficient, precise, and scalable, has inspired a gold rush of countless applications in medicine, agriculture and basic science. Early areas of focus include genetic diseases such as sickle cell and hereditary ATTR amyloidosis, offering new and exciting optimism.

Ground-Breaking Science in Gene Editing

“A genome is an organism’s complete set of DNA, including all of its genes. Each genome contains all of the information needed to build and maintain that organism. In humans, a copy of the entire genome – more than three billion DNA base pairs – is contained in all cells that have a nucleus.”  – Intellia Therapeutics

CRISPR, short for Clustered Regularly Interspaced Short Palindromic Repeats, is a microbial ‘immune system’ that prokaryotes — bacteria and archaea — use to prevent infection by viruses called phages. At its core, the CRISPR system gives prokaryotes the ability to recognize precise genetic sequences that match a phage or other invaders and target these sequences for destruction using specialized enzymes.

Previous work had identified these enzymes, known as CRISPR-associated proteins (Cas), including one called Cas9. But scientist Emmanuelle Charpentier, working first at the University of Vienna and later at the Umeå Centre for Microbial Research in Sweden, identified another key component of the CRISPR system, an RNA molecule that is involved in recognizing phage sequences, in the bacterium Streptococcus pyogenes, which can cause disease in humans.

Charpentier reported the discovery in 2011 and that year struck up a collaboration with American biochemist Jennifer Doudna. In a landmark 2012 paper in Science, the duo isolated the components of the CRISPR–Cas9 system, adapted them to function in the test tube and showed that the system could be programmed to cut specific sites in isolated DNA – an incredibly precise set of DNA-editing genetic scissors. In 2020, Doudna and Charpentier won the 2020 Nobel Prize in Chemistry for their gene-editing technology.

“The ability to cut DNA where you want has revolutionized the life sciences,” said Pernilla Wittung Stafshede, a biophysical chemist and member of the Nobel chemistry committee, at the prize announcement. “The ‘genetic scissors’ were discovered just eight years ago, but have already benefitted humankind greatly.”

 

How Does CRISPR/Cas9 Work? (3)

This technology acts as an incredibly precise set of molecular scissors, providing instructions to cut an identified gene in a specific position in the nucleus of DNA. There are two primary components to the CRISPR/Cas9 genome editing system:

  • The Cas9 protein, which initially recognizes the DNA and also acts like a pair of “molecular scissors” that precisely cleaves the targeted DNA sequence.
  • The guide RNA, which guides the Cas9 scissors to the desired target DNA sequence and activates the scissors so they cut.

https://www.intelliatx.com/crisprcas9/how-crisprcas9-works/

Background on Hereditary Transthyretin Amyloidosis (hATTR/ATTRv) (1)

Transthyretin amyloidosis is a slowly progressive condition characterized by the buildup of abnormal deposits of a protein called amyloid (amyloidosis) in the body’s organs and tissues. These protein deposits most frequently occur in the peripheral nervous system, which is made up of nerves connecting the brain and spinal cord to muscles and sensory cells that detect sensations such as touch, pain, heat, and sound. Protein deposits in these nerves result in a loss of sensation in the extremities (peripheral neuropathy). The autonomic nervous system, which controls involuntary body functions such as blood pressure, heart rate, and digestion, may also be affected by amyloidosis. In some cases, the brain and spinal cord (central nervous system) are affected. Other areas of amyloidosis include the heart, kidneys, eyes, and gastrointestinal tract. The age at which symptoms begin to develop varies widely among individuals with this condition, and is typically between ages 20 and 70.

There are three major forms of transthyretin amyloidosis, which are distinguished by their symptoms and the body systems they affect.

  1. The neuropathic form of transthyretin amyloidosis primarily affects the peripheral and autonomic nervous systems, resulting in peripheral neuropathy and difficulty controlling bodily functions.
  2. The leptomeningeal form of transthyretin amyloidosis primarily affects the central nervous system.
  3. The cardiac form of transthyretin amyloidosis affects the heart.

Mutations in the TTR gene causes the liver to product the TTR protein in a misfolded form. This misfolded protein can then build up in the body and lead to disease-causing nerve and other organ damage.

 

Clinical Trial Research (4)

According to CRISPRMedicineNews, one of the early clinical trials within gene editing is focused on hereditary transthyretin amyloidosis. In these trials, CRISPR-Cas is either used directly to treat the condition by editing an individual’s genome in vivo or indirectly through ex vivo engineering of a cell-based therapy. An update published November 17, 2020 discusses the clinical trial, which is now underway in the U.K.

CRISPR-Cas9 Trial For NTLA-2001 to Treat Hereditary Transthyretin Amyloidosis With Polyneuropathy

The second newly-added trial is sponsored by US-based Intellia Therapeutics and seeks to enroll 38 participants who are diagnosed with polyneuropathy (PN) due to transthyretin (TTR) amyloidosis (ATTR).

This open-label Phase 1 two-part trial comprises a dose escalation followed by a safety dose expansion study to evaluate the safety, tolerability, pharmacokinetics and pharmacodynamics of Intellia’s most advanced in vivo CRISPR-based therapy candidate, NTLA-2001.

ATTR is a hereditary progressive condition that is characterized by an accumulation of misfolded transthyretin (TTR) protein. The disease results from mutation(s) in the TTR gene, leading to mutant TRR protein that is unstable and easily forms aggregates that deposit as amyloid in various organs and tissues in the body. Organs or body parts most often affected include the nerves, heart, kidneys and eyes.

Life expectancy is typically 2-15 years from disease onset, and current treatment options include transplantation of affected organs and medications to slow progression of disease symptoms.

NTLA-2001 is the first investigative CRISPR-based therapy to be administered in vivo in humans. The new therapy comprises TTR-targeting gRNA and Cas9 mRNA, both of which are delivered in vivo via Intellia’s proprietary lipid nanoparticle technology. Pre-clinical studies support the notion that NTLA-2001 has potential as a one-time curative treatment. The first patient was dosed with NTLA-2001 last week and the study is expected to be completed in 2024.

Worldwide prevalence of spontaneous and hereditary transthyretin amyloidosis (ATTR). Source: Intellia Therapeutics. https://www.intelliatx.com/in-vivo-therapies/

 

Potential Game-Changer for Hereditary ATTR Amyloidosis

 “Once we’ve assessed safety and established an optimal dose, we intend to rapidly initiate trials for the clinical manifestations of ATTR. NTLA-2001 may halt and reverse ATTR progression by producing a deeper, permanent TTR protein reduction for all patients – regardless of disease type – than the chronically administered treatments currently available.” said Intellia Therapeutics President and CEO, John Leonard, M.D.

 Intellia’s proprietary CRISPR/Cas9 system could potentially address diseases with a single course of treatment because it permanently repairs the defective DNA. This represents a breakthrough improvement over current therapies, most of which require lifelong administration because they cannot correct underlying causes of the disease. However, this technology does not pass the genetic changes made to the patient to his or her offspring … the “fix” will not pass from generation to generation.

 

This is exciting news, giving new hope for families who have been ravaged by disease over generations.

 

 

 

 

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If you’d like to read more about Jennifer Doudna, here’s a book recently released by bestselling author Walter Isaacson, The Code Breaker.

 

Sources:

  1. https://crisprmedicinenews.com/clinical-trial/transthyretin-amyloidosis-attr-nct04601051/
  2. crisprmedicinenews.com
  3. https://www.intelliatx.com
  4. https://crisprmedicinenews.com/news/crispr-cas-clinical-trial-update/
  5. https://www.nature.com/articles/d41586-020-02765-9
  6. Doudna Lab, Berkeley, California
  7. CRISPR Therapeutics, Cambridge, Massachusetts
  8. Innovative Genomics Institute, Berkeley, California

 

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