The Bones of Harry Eastlack

While playing with his sister, 5-year-old Harry Eastlack broke his leg.  He was taken to the hospital to set the fracture, but it never healed properly.  Then, at age 10, Harry’s knee and hip joints stiffened. Strange lumps formed in his thigh muscle – lumps of bone.  When surgeons removed these lumps, new bone growths appeared in their place, larger and more extensive than before.  By age 20, all of the vertebrae in Harry’s spine had fused into one piece and his most of his back muscles had ossified into boney plates.  Harry’s muscles, tendons, and ligaments were slowly turning into bone [1].  He suffered from an extremely rare disorder, called fibrodysplasia ossificans progressiva or FOP, caused by a mutation in this week’s gene of interest: activin receptor-like kinase-2 or ALK-2.

FOP is the body’s repair mechanism gone awry.  Normally injuries are repaired by regenerating wounded tissue. Tear a muscle, new muscle regrows in its place.  But people with FOP ‘heal’ connective tissue (muscle, tendons, and ligaments) by converting the wounded tissue into bone, spontaneously or upon injury [2].  Even small wounds, like a needle prick from an injection, can form tiny bone spurs under the skin.  FOP sufferers dread bumps or falls – a car crash would be a nightmare – because any injury might be ‘healed’ by bone growth that permanently locks the affected joints in place.  Even without injury, the disease progresses through the body from top to bottom, starting at the neck, then shoulders, arms, around the ribs, and finally the legs and feet [3].  Over time, each joint turns to bone, locking limbs at awkward angles and slowly converting a person into a living statue.

Again, bone formed in FOP isn’t new bone growth, but conversion of normal tissue into bone.  While that sounds pretty disturbing, it’s not a completely abnormal process, but takes its roots in normal bone development.

As I mentioned in an earlier post, bone is a living tissue, with the potential to grow, adapt, and heal itself.  There are two ways bones form [4].  One, intramembranous ossification, forms thin plates of bone like those found in the skull.  The other, endochondral ossification, starts with a template of cartilage that’s converted into bone.  This is how most of the bones in the skeleton are formed.  A temporary cartilage skeleton develops and is replaced with bone, converting one type of tissue into another.  Exactly like FOP.

1) A cartilage template forms.  Chondrocytes (cartilage-forming cells) in the center start to die off leaving small cavities.  2) Cells around the shaft of the cartilage template convert into osteoblasts (bone-forming cells).  The osteoblasts create a sheath of bone around the template.  3) Blood vessels invade the center of the template.  Fibroblasts (wound healing cells) migrate in through the blood vessels and convert into osteoblasts.  These newly-converted osteoblasts produce bone, forming the primary ossification center.  4) The marrow cavity forms in the center.  Secondary ossification centers develop at each end.  5) The left over cartilage between ossification centers forms the growth plate, allowing the bone to grow and lengthen through adolescence.  6) The growth plate is replaced with bone in adulthood.  Cartilage remains only at the joints.

Bone growth in controlled by a set of growth factors called bone morphogenic proteins or BMPs [5].  Similar to the receptor Her2, BMP signals its bone-growth message through a set of cellular receptors that sit on the outside of the cell.  One of those receptors is ALK-2.  When BMPs interact with ALK-2, it sends pro-bone signals into the cell.

Harry Eastlack’s Skeleton on display at the Mutter Museum.  Source: Joh-co / Wikimedia Commons

In FOP, a single amino acid in ALK-2 is switched with another [6].  This mutation leaves ALK-2 in the ‘on’ position, allowing it to send pro-bone signals even without the presence of BMP growth hormones.  With this signal always on, it takes very little for cells in the body to undergo the transition similar to that found in endochondral ossification – and convert normal tissues into bone.

Much of what we know about FOP is thanks to Harry Eastlack and his skeleton, on display at The Mütter Museum of The College of Physicians in Philadelphia [1].  By the end of his life, Harry’s skeleton had fused into one solid piece.  He could only move his lips.  On his death bed, just a few days shy of his 40th birthday, he asked to donate his body to science, hoping it would help scientists understand this horrifying disorder.  The bridges and plates wrapping his skeleton like papier-mâché pointed to uncontrolled endochondral ossification.  This valuable hint helped identify the ALK-2 mutation which might eventually lead to a cure.

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References
[1] “Bone, A Masterpiece of Elastic Strength”. New York Times. 27 April 2009. 
[2] van Dinther, M.; Visser, N.; de Gorter, D.J.; Doorn, J.; Goumans, M.J.; de Boer, J.; ten Dijke, P. (2011) “ALK2 R206H mutation linked to fibrodysplasia ossificans progressiva confers constitutive activity to the BMP type I receptor and sensitizes mesenchymal cells to BMP-induced osteoblast differentiation and bone formation”. J Bone Mineral Res. 25 (6): 1208-15. PMID 19929436.
[3] “FOP Symptoms”. IFOPA. 2009.
[4] Gilbert SF (2000) “Osteogenesis: The Development of Bones”. Developmental Biology. 6th edition. Sunderland (MA): Sinauer Associates.
[5] Chen, D.; Zhao, M.; Mundy, G.R. (2004) “Bone morphogenetic proteins”. Growth Factors 22(4): 233-41. PMID 15621726
[6] Shore, E.M.; Xu, M.; Feldman, G.J.; et al. (2006). “A recurrent mutation in the BMP type I receptor ACVR1 causes inherited and sporadic fibrodysplasia ossificans progressiva”. Nat. Genet. 38(5): 525–27. PMID 16642017.

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If You Believe in Medicine

Ever heard of a snake oil salesman?  Back in the old west, doctors would drift into town peddling miracle tinctures purported to cure anything from rheumatism to deafness.  Greatest pain remedy on earth!  Money back if it fails!  The doc would sell his elixirs and mosey out of town before anyone realized his “medicines” were worthless.

As part of a suit in 1917, the US government tested the snake oil made by Clark ‘the Rattlesnake King’ Stanley (pictured here) [1]. It contained mineral oil, fatty oil, red pepper, turpentine, camphor, and not one iota of snake!  Clark Stanley was fined $20 for misbranding and the term “snake oil salesman” has been synonymous with charlatan ever since.

But you’d never fall for the medicine man’s miracle cure, right?  Maybe, maybe not. As with everything on my blog, that might depend on your genes, particularly your copy of this week’s gene of interest:  Catechol-O-methyltransferase or COMT.

Snake oil is an example of a placebo, and if it cured what ailed ya, it was probably due to the placebo effect.  Just the act of taking medicine can make someone feel better.  Fake injections, sham surgeries, really any active medical intervention can elicit a placebo effect that results in real measurable changes in physiology [2].  Placebos can affect heart rate, blood pressure, brain chemistry and patients’ reported severity of pain, depression, anxiety, and fatigue [3].

While these improvements aren’t just in your head, the success of a placebo is all in the way you sell it.  If a placebo is presented as a stimulant it can increase heart rate and blood pressure, but if presented as a depressive, the same pill will have the opposite effect [4].  Even the color of the pill is important, red is better for uppers, blue for downers [5].  And without salesmanship, sometimes the effects of actual drugs can be deadened entirely.  If patients are unaware they’re receiving pain medication, it is much less effective.  They’ll still report pain despite unknowingly being treated.  So, while duping a patient into believing in a treatment sounds ethically dubious, it might be an important part of medicine.

All of this points to the brain’s powerful ability to control our health.  One theory suggests that the body will hold off on its own self-preservation measures (like fever in response to infection) if the brain believes it’s being cared for by someone else – if it believes the medical treatment being administered will work [6].

But this effect can complicate the development of new therapies.  In clinical trials, patients treated with new drugs have to be compared to a control group to determine if the drug has any benefit at all.  Often studies will be double-blinded, meaning neither the patient nor the doctor has any idea which treatment (placebo or the real deal) is being administered.  That’s because any new treatment could act like a placebo with patients reporting benefits when actually the drug does nothing at all.

But not all trial subjects are created equal.  A study was recently published that identified a certain variant of the COMT gene linked with the placebo effect [7].

COMT is one of several genes that encode an enzyme responsible for breaking down neurotransmitters like dopamine [8].  This enzyme therefore has powerful effects on your perception of well-being.  People with one variant of the COMT gene are more likely to fall for the placebo effect.  When given fake acupuncture treatment for irritable bowel syndrome, people with this variant were more likely to believe in the acupuncture treatment and report a reduction in pain.

COMT may be the first gene linked with the placebo effect, but there are likely others – different genes may be associated with different health markers.  In the future, scientists may sequence your genetics to determine whether you’re a good candidate for a clinical trial or someone easily duped by the snake oil salesmen.

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References
[1] Nickell, J (1998) “Peddling Snake Oil; Investigative Files“. Skeptical Inquirer (Commitee for Skeptical Inquiry) 8(4). 
[2] Wechsler, M.E.; Kelly, J.M.; Boyd, I.O.; Dutile, S.; Marigowda, G.; Kirsh, I.; Israel, E.; Kaptchuk, T.J. (2011) “Active albuterol or placebo, sham acupuncture, or no intervention in asthma”. New England Journal of Medicine. 365 (2): 119-126. PMID 21751905.
[3] “The Placebo Phenomenon”. Harvard Magazine. February 2013.
[4] Kirsh, I. (1997) “Specifying non- specifics: Psychological mechanism of the placebo effect.” In Harrington, A. The Placebo Effect: An Interdisciplinary Exploration. Cambridge: Harvard University Press. pp. 166-86.  ISBN 978-0-674-66986-4.
[5] de Craen, A.J.; Roos, P.J.; Leonard de Vries, A.; Kleijnen, J. (1996) “Effect of colour of drugs: systematic review of perceived effect of drugs and of their effectiveness”. BMJ 313(7072): 1624-6. PMID 8991013
[6] Humphery, N. (2002) “Great Expectations: The Evolutionary Psychology of Faith-Healing and the Placebo Effect”. The Mind Made Flesh: Essays from the Frontiers of Psychology and Evolution. Oxford University Press. pp. 255-85. ISBN 978-0-19-280227-9.
[7] “Is the Placebo Effect in Some People’s Genes?”.  Reuters. 16 April 2015.
[8] Grossman, M.H.; Emanuel, B.S.; Budarf, M.L.; (1992) “Chromosomal mapping of the human catechol-O-methyltransferase gene to 22q11.1-q11.2”. Genomics 12(4): 822-5. PMID 1572656.

Cancer: Mutiny Inside the Body

Why is there no cure for cancer?  For a simple reason: cancer is complex.  The complexity stems from the genetics of cancer – genetics distinct from the rest of the body [1].  Because of this complexity, scientists have learned to be creative in the search for treatments, and the story of this search includes this week’s gene of interest: human epidermal growth factor receptor 2 or HER2.

Ever since multicellular organisms evolved, it’s been a challenge to get every cell to work together for the good of the group.  That’s weird, right?  You think of yourself as an individual, but you are composed of trillions of cells – trillions of individual living things.  Before multicellular organisms evolved, each cell was independent.  When groups of cells started working together for survival, it required a monumental amount of control.  A large portion of your genome exists to maintain that control.  Layer upon layer of checks and balances to keep everyone on the same page.

 

 

Many of these checks and balances control when a cell should divide and when it should die, especially if there’s DNA damage.  Cells regularly check themselves for DNA damage and commit suicide before it becomes a problem.  If you’ve ever had a sunburn, you’ve seen this effect in action [2].  After prolonged exposure to the sun, skin cell DNA suffers damage from UV radiation.  Detecting this damage, skin cells begin to destroy themselves.  After their death, the immune system increases blood flow and inflammation to the area to help with healing.  That’s why sunburns don’t appear right away.  Sometimes it’s not until after the sun sets that you notice you should have probably worn sunscreen that day.

Cells with DNA damage try to destroy themselves before they develop too many harmful mutations (oncogenes) that might allow the cell to divide and ignore the control of the genome [3].  One such mutation can occur in HER2, an oncogene associated with aggressive breast cancer.

HER2 is a cellular receptor, which means it located on the outside of the cell [4].  Receptors are used in cell communication, waiting for signals from molecules outside of the cell, and then transmitting that signal to the inside of the cell.  The HER2 receptor is responsible for relaying growth signals.  In breast cancer, a mutation can occur resulting in too many copies of the HER2 gene.  The cell then produces too many HER2 receptors (called overexpression) making it oversensitive to growth signals.

Cancer cells divide rapidly, so many cancer therapies (specifically chemotherapy) work by attacking any cell that’s dividing, including healthy cells like hair follicles and cells that line the digestive track.  This results in awful side effects like hair loss, mouth sores, nausea, and other digestive issues [5].

Chemotherapy works as a cancer treatment, but it’s not very specific, hence all the side effects.  To improve cancer treatment, scientists look for specific markers.  The HER2 receptor sits on the outside of the cell, making a great marker.  A drug called Herceptin hones in and binds to HER2, blocking it’s growth signal and slowing this type of cancer [6].

Herceptin has dramatically improved the survival rate of people with this aggressive form of breast cancer.  But it only works if the cancer cells overexpress HER2.  Overexpression is rare, found in just 20 – 25% of breast cancer cases, and Herceptin has its own set of dangerous side effects.  HER2 overexpression has to be verified before treatment begins, usually by staining a section of the tumor as seen below [6].

Human breast tissue stained for HER2 expression. A biopsy is taken from a tumor, sectioned, and stained for HER2 in brown. Cell nuclei are stained in blue. The dark brown stain indicates that this tissue is HER2 positive. Source: KGH / Wikimedia Commons

And that’s why we haven’t found a cure for cancer: each cancer is different.  Confusingly, we name cancer by its source tissue (e.g. breast cancer), but there are several different types of breast cancer, each with its own unique genetic profile.  Many, many genes have to mutate before a cell becomes cancerous, so a cancer cell’s genetic profile is unique, even from the surrounding healthy tissue.  Treatments are much more successful if they are personalized to the genetics of the disease.

Testing for HER2 overexpression and treating with Herceptin is a great example of personalized medicine, an approach that’s becoming more and more common for cancer treatment [7].  Personalized treatments for breast cancer have been around for a while.  Simple stains (like the one pictured above) identify the type of cancer and the best treatment options.  With the development of genetic testing, we’re even able to predict chemotherapy effectiveness and the chance for recurrence based on a cancer cell’s genetic profile.

Cancer is complex, but maybe if we embrace this complexity, personalizing treatments to genetics of the disease, we’ll find our way to a cure.

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References
[1] “The Genetics of Cancer”.  National Cancer Institute. 22 April 2015.
[2] “The Science of Summer: What Causes Sunburns?”. Live Science. 9 July 2013.
[3] Norbury, C.J.; Zhivotovsky, B. (2004). “DNA-damage induced apoptosis”. Oncogene. 23(16): 2797-808. PMID 15077143.
[4] “Her2 Status”. BreastCancer.org. 23 October 2015.
[5] “Chemotherapy Drugs: How They Work”. American Cancer Society. 6 February 2015.
[6] “Herceptin”. BreastCancer.org. 5 November 2015.
[7] “How Personalized Medicine is Changing Breast Cancer”.  Genome.

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Edited 1/12/2016:

The Washington Post recently posted this article about the rise of multicellular life.  Ken Prehoda at University of Oregon believes he’s discovered the mutation that allowed cells to cooperate by studying the DNA of choanoflagellates – our closets living unicellular cousins.  Although usually independent, occasionally these choanoflagellates cooperate by clumping together with their flagella (tails) pointed outward.  This makes my cartoon look more like a well researched diagram and less like a pile of hairy olives!  (high fives self)

This “cooperation gene” might even be linked to development of cancer.  Read more at the link above.

The Fantastical Tardigrade

Image by Bob Goldstein and Vicky Madden Via Wikimedia Commons

There are adorable super beings hiding in the dirt.  Nearly indestructible tardigrades (Latin for “slow stepper”, pronounced TAR-dee-grade) commonly known as water bears [1].  Less than a millimeter long, their pudgy bodies are made up of only 40,000 cells.  They have 4 pairs of legs each ending in tiny claws and a pronged sucker for a mouth [2].  Isn’t it cute?

These little guys can thrive anywhere: hot springs, deep water trenches, even the Antarctic [1].  Their ability to adapt to any environment has made scientists curious.  How much can water bears handle?  What are their limits?

So far we know that water bears can survive in sub-freezing and boiling temperatures (from -272°C (-458°F) to 149°C (300°F))[3].  They can also survive for years without water and they’re also resistant to radiation, surviving levels 100 times the lethal dose for humans [4].

They can even survive in the vacuum of space.  In 2007, thousands of water bears were launched into orbit and exposed to the vacuum of space for 10 days.  After returning to Earth, researchers found that 68% of the water bears survived [4].  Some of the females had even laid eggs while in space and the space-laid young hatched perfectly healthy.  This makes tardigrades the only animal to have ever survived the vacuum of space.

We’re still not sure how water bears manage to be so indestructible, but a recent study points to a sort of natural genetic engineering.

In an earlier post, I described how genetic engineering lets scientists insert a gene from one organism (like the gene for human insulin) into another organism (like bacteria).  Scientists thought they were clever trading genes between different species, but apparently this has been happening naturally for millions of years, in a process called horizontal gene transfer.

The most well-known example of horizontal gene transfer is antibiotic resistance in bacteria.  Different species of bacteria regularly trade small bits of DNA.  If one strain of bacteria develops resistance to an antibiotic, it can transfer that gene to a completely different species.  This transfer of useful genes can happen between almost any species.  Even humans have even collected a few genes from simpler organisms like bacteria [5].

A genomics lab at the University of North Carolina sequenced the water bear genome and found that 17.5 percent its DNA had come from horizontal gene transfer, higher than any known organism [2].  This DNA was foreign – it didn’t fit the pattern of the rest of the water bear’s genome.  Instead they matched genes found in bacteria, plants, and fungi [6}.  The lab guessed that this might explain the water bear’s extreme adaptability.  It was stealing genes from other organisms in the environment, organisms that had already developed genes to adapt to extreme conditions.

Water bears engineering themselves to be indestructible would be pretty amazing, but the story doesn’t end there.  Another lab in Edinburgh has called the study from UNC into question [7].  The Edinburgh lab also sequenced the water bear’s genome, but found that foreign DNA accounted for only 2% of the water bear’s genome, a percentage common among many other less impressive organisms (humans have less than 1%) [5, 8].

The Edinburgh lab argues that the UNC study may have accidentally counted contaminating DNA as part of the water bear’s genome.  Water bears live in dirt, so bacteria, bits of plants, and fungi were probably collected along with the water bears and combined into one DNA sample.  Because DNA from a water bear or a plant all looks alike, it’s hard to identify its source.  The Edinburgh lab used a technique that identified rare genes and eliminated them as probable contamination [8].  They identified far fewer transferred genes, which means water bears may not adapt to their environment by stealing genes from other organisms.

This back and forth in science is common.  Many independent labs working on the same problem cross-check each other’s results to eliminate errors.   Science is constantly checking and rechecking itself.   It’s only after years of independent studies that a consensus is finally reached, but at any time new research can up-end even established scientific principles.

It also means the indestructible water bear is still an adorable little mystery.

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References
[1] “The Tardigrade: Practically Invisible, Indestructible ‘Water Bears'”.  The NY Times. 7 September 2015.
[2]  “Water Bears: Genome Sequence Says It Has Most Foreign DNA Of Any Animal”. Nature World News. 26 November 2015.
[3] “Absurd Creature of the Week: The Incredible Critter That’s Tough Enough to Survive in Space”. Wired. 21 March 2014.
[4] “Tardigrades Return from the Dead”. BBC. 13 March 2015.
[5] “Humans may harbor more than 100 genes from other organisms”. Sciencemag. 12 March 2015.
[6] Boothby, T.; Tenlen, J.; Smith, F.; Wang, J.; Patanella, K.; Osborne Nishimura, E.; Tintori, S.; Li, Q.; Jones, C.; Yandell, M.; Messina, D.; Glasscock, J.; Goldstein, B. (2015). “Evidence for extensive horizontal gene transfer from the draft genome of a tardigrade”. Proc Natl Acad Sci Nov 23: pii: 201510461. PMID 26598659.
[7] “Rival Scientists Cast Doubt Upon Recent Discovery About Invincible Animals”.  The Atlantic.  4 December 2015.
[8] Koutsovoulos, G.; Kumar, S.; Laetsch, D.; Stevens, L.; Daub, J.; Conlon, C.; Maroon, H.; Thomas, F.; Aboobaker, A.; Blaxter, M. (2015). “The genome of the tardigrade Hypsibius dujardini”. bioRxiv: 033464.