Rare Disease Sleuths Uncover New Clues to Stroke

Posted on February 25th, 2014 by Dr. Francis Collins

A medical mystery that began when a 3-year-old girl came to the NIH Clinical Center here in Bethesda, MD, a decade ago has just been solved. The findings not only promise to help children suffering from a devastating rare disease, but to advance our overall understanding of stroke and other blood vessel disorders.

When researchers first met the little girl, they were baffled. She had a most unusual—and unexplained—constellation of symptoms: recurring fevers, rashes, and strokes, which, sadly, had left her severely disabled. Researchers thought the cause probably wasn’t genetic, because none of the girl’s family members were affected, plus they hadn’t seen other children with similar problems. While they searched for clues, they treated the girl with immunosuppressive drugs to reduce blood vessel inflammation and thereby lower the chance of future strokes.

Several years passed, but then two unrelated children with very similar symptoms came to NIH. Like the first little girl, both of these youngsters (a 6-year-old girl and 6-year-old boy) had suffered strokes before the age of 5. The additional patients—along with recent advances in DNA sequencing technology—offered researchers the opportunity to explore more fully whether a gene mutation might be responsible for this puzzling disorder.

So, intramural scientists from seven NIH Institutes and Centers teamed up to sequence and analyze the exomes—the protein-coding part of the genomes—of all three affected children and their unaffected parents. That was no small feat, because although the exome makes up less than 2% of the human genome, it still contains about 30 million DNA letters. Sequencing efforts of this scale have only become feasible in the last few years, thanks to the development of faster, cheaper sequencing technologies.

When the researchers examined the genetic data, they discovered all three children had two mutated copies of the CECR1 gene—one copy from each of their parents. In contrast, their parents each carried one normal copy and one mutated copy of the CECR1 gene.

The CECR1 gene codes for an enzyme called adenosine deaminase 2 (ADA2), which is crucial for blood vessel development and maintaining the balance of key immune cells called monocytes and macrophages. The mutated copies of CECR1 found in the young patients impair their ability to produce the ADA2 enzyme. This ADA2 deficiency, the researchers found, leads to vascular and immune system abnormalities that promote a vicious cycle of inflammation that, in turn, raises the risk of stroke.

The discovery of what underlies this rare blood vessel disease may also benefit efforts to treat and prevent a much more common vascular disorder: stroke. More than 800,000 Americans suffer a stroke each year, and it remains our nation’s fourth leading cause of death. Intriguingly, at least one previous study has found that adults who carry one CERC1 mutation may face an increased risk of late-onset stroke [2]. Building on the new findings, it is now possible to delve further into the role of the ADA2 pathway in stroke and other blood vessel disorders.

To verify their initial findings, the NIH researchers sequenced the CECR1 gene in six more patients with somewhat similar symptoms. Two of those patients were from the NIH Clinical Center, one was from the United Kingdom, and three were from Turkey.

Unlike the other patients, the Turkish patients had no history of stroke, but had a systemic, inflammatory vascular disease called polyarteritis nodosa (PAN).

The sequencing work found that all six additional patients had two mutated copies of CECR1. However, the PAN patients had mutations in a different part of the gene than those who had suffered strokes. Such a finding has lots of precedents: for many genetic diseases, mutations in different parts of the same gene can produce different forms of disease.

The NIH discoveries overlap with those of an Israeli team, which found similar CECR1 mutations among PAN patients of Georgian (as in the nation) Jewish, German, and Turkish ancestry [3]. Preliminary research also shows the same mutation seen among NIH’s Turkish PAN patients and the Georgian Jewish PAN patients exists in some Middle Eastern and Pakistani populations, so it may be more prevalent than originally thought.

To learn more about the function of the CECR1 gene, NIH researchers turned to an animal model: zebrafish. When these tiny, transparent fish were genetically engineered to produce lower amounts of the ADA2 enzyme, they experienced immune cell imbalances and bleeding in the brain, similar to that seen in some of the children with ADA2 deficiency.

The researchers have dubbed the newfound disease “Deficiency of ADA2,” or DADA2.  But identifying the cause of the disorder is just the beginning. Now, the hope is that this information can be used to find better treatments and, hopefully, someday a cure. One possibility is to use drugs that are more specifically aimed at reducing inflammation in the arteries. Another approach is to replace the missing ADA2 enyzme, perhaps using fresh-frozen plasma, an artificial form of the protein, or even a bone marrow transplant.

References:

[1] Early-Onset Stroke and Vasculopathy Associated with Mutations in ADA2. Zhou Q, Yang D, Ombrello AK, Zavialov AV, Toro C, Zavialov AV, Stone DL, Chae JJ, Rosenzweig SD, Bishop K, Barron KS, Kuehn HS, Hoffmann P, Negro A, Tsai WL, Cowen EW, Pei W, Milner JD, Silvin C, Heller T, Chin DT, Patronas NJ, Barber JS, Lee CC, Wood GM, Ling A, Kelly SJ, Kleiner DE, Mullikin JC, Ganson NJ, Kong HH, Hambleton S, Candotti F, Quezado MM, Calvo KR, Alao H, Barham BK, Jones A, Meschia JF, Worrall BB, Kasner SE, Rich SS, Goldbach-Mansky R, Abinun M, Chalom E, Gotte AC, Punaro M, Pascual V, Verbsky JW, Torgerson TR, Singer NG, Gershon TR, Ozen S, Karadag O, Fleisher TA, Remmers EF, Burgess SM, Moir SL, Gadina M, Sood R, Hershfield MS, Boehm M, Kastner DL, Aksentijevich I. N Engl J Med. 2014 Feb 19.

[2] The Siblings With Ischemic Stroke Study (SWISS) protocol. Meschia JF, Brown RD Jr, Brott TG, Chukwudelunzu FE, Hardy J, Rich SS. BMC Med Genet. 2002;3:1.

[3] Mutant Adenosine Deaminase 2 in a Polyarteritis Nodosa Vasculopathy. Elkan PN et al. N Engl J Med. 2014 Feb 19.

Links:

Boy suffering from mystery strokes get diagnosis, TODAY, NBC, 2013 May 9

NIH Undiagnosed Diseases Program

NIH support: Intramural Research Programs; National Human Genome Research Institute; National Heart, Lung, and Blood Institute; National Institute of Allergy and Infectious Diseases; National Institute of Arthritis and Musculoskeletal and Skin Diseases; National Cancer Institute; National Institute of Diabetes and Digestive and Kidney Diseases; Clinical Center