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Ricki Lewis

Genetic Linkage

Autism Gene Discovery Recalls Alzheimer’s and BRCA1 Stories

March 26, 2015
Tags: Autism, Alzheimer's disease, BRCA1 breast cancer
Discovery of a new gene behind autism cleverly combines genetic techniques new and classic.

Autism has been difficult to characterize genetically. It is probably a common endpoint for many genotypes, and is a multifactorial (“complex”) trait. That is, hundreds of genes contribute risk to different degrees, as do environmental factors. Research reports implicate either dozens of genes in genomewide sweeps, or focus on a few genes that encode proteins that act at synapses, such as the < href="https://www.autismspeaks.org/science/grants/neuroligins-and-neurexins-autism-candidate-genes-study-their-association-synaptic-con">neuroligins and neurexins. Read More 
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CRISPR Meets iPS: Technologies Converge to Tackle Sickle Cell Disease

March 15, 2015
Tags: CRISPR, iPS, sickle cell disease, genome editing
Researchers from Johns Hopkins University have teamed two powerful technologies to correct sickle cell disease in a lab dish. Linzhao Cheng and colleagues have deployed CRISPR/Cas-9 on iPS cells to replace the mutant beta globin gene, published in Stem Cells.

ACRONYMS AND ABBREVIATIONS

CRISPR conjures up images of fried chicken, but it stands for “clustered regularly interspaced short palindromic repeats” – short repeated DNA sequences interspersed with areas called spacers, like stutters. The pattern of repeats and spaces attracts an enzyme, Cas9, which is like a molecular scissors that cuts wherever short RNA molecules called “guide RNAs” take it. Here’s a fuller description. Read More 
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The Man Who Ate 25 Eggs a Day

March 6, 2015
Tags: cholesterol, statin, triglyceride, South Beach Diet, genetic testing
Cholesterol isn't the enemy -- triglycerides are.
Each morning at the retirement community, the healthy 88-year-old man received a delivery of 25 soft-boiled eggs, which he would consume during his day. This had been his way for many years. He’d had one experience of chest pain that might have been angina, but aside from that, he had a healthy cardiovascular system. He recognized that his only problem was psychological: “Eating these eggs ruins my life, but I can’t help it.”

I think of the Eggman, a brief case report from 1991 in the New England Journal of Medicine, whenever "news" of cholesterol’s unsuitability as a one-size-fits-all biomarker resurfaces, as it does every few years and did again a few weeks ago. Read More 
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Using the Genetic Code for Passwords

December 7, 2014
Tags: genetic code, DNA, RNA, amino acids
Many years ago, a friend was helping me set up a desktop computer. When the time came to choose a password, he said it should be:

• Alphanumeric
• More than 7 numbers or letters
• Obvious to me, but not to anyone else

The genetic code popped into my mind, and has remained an endless source of diverse passwords, valuable because they may seem nonsensical to non-biologists.  Read More 
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When Mutation Counters Infection: From Sickle Cell to Ebola

November 19, 2014
Tags: balanced polymorphism, Ebola, sickle cell, cystic fibrosis, natural selection, Niemann-Pick C1, PKU, genetic disease, prions, mad cow disease
Balanced polymorphism retains mutant genes in populations when they protect against other conditions.
While pharmaceutical companies focus on drug discovery for Ebola virus disease, a powerful clue is coming from a rare “Jewish genetic disease” that destroys the brain. People with Niemann-Pick C1 disease can’t get Ebola, adding to the list of disease pairs that arise from a fascinating form of natural selection.

Balanced polymorphism, aka heterozygote advantage, is a terrific illustration of ongoing evolution. And it pits the human body against all sorts of invaders – prions, viruses, bacteria, protozoa, and fungi. Read More 
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Eman Reports from Ebola Ground Zero

November 19, 2014
Tags: Ebola, Liberia, Emmanuel Gokpolu, Ricki Lewis
Eman (arrow) at an Ebola awareness workshop a few weeks ago. He is in the hospital now, with a fever, but has tested negative for Ebola.
My last post continued Emmanuel Gokpolu’s reporting from Ebola ground zero in Liberia. Ebola interrupted Eman’s medical education, so now he is educating his people about strategies to minimize risk of infection.

Eman and I began a very special friendship when he first contacted me when using my human genetics textbook in college. Right now he is in a hospital with a fever, after finally convincing the staff to admit him. It might be a flare-up of his malaria, we don't yet know.

This post picks up in early October, when Ebola suddenly jumped from a topic rarely reported in the U.S. ,to major news when it arrived here.  Read More 
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Eman’s Emails from Liberia: Through September

October 24, 2014
Tags: Ebola, Liberia, virus, epidemiology, Monrovia
Emmanuel Gokpolu with his son, little Larry
Emmanuel Gokpolu, who lives in Liberia, calls me Mom, although he has a wonderful real mother. In Africa, family isn’t only about DNA.

Eman contacted me in 2007, after using my human genetics textbook in college. My husband Larry and I had been putting him through medical school in Monrovia -- until Ebola happened. Now the funds go for gloves, long sleeve shirts, detergents, food and medicine, to keep Eman and his family, including his almost-one-year-old son, Larry, safe.

This week Eman asked me to share his emails, which began arriving before many people here had heard of Ebola virus disease, or cared much about it if they had. The disease seemed, and was, half a world away.

The world is a small place. Read More 
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SCID-X1 Gene Therapy, Take 2

October 12, 2014
Tags: gene therapy, bubble boy, SCID-X1, ADA deficiency, forever fix
David Vetter had SCID-X1 and became known as the bubble boy. (NASA)
Beneath all the bad news about viruses this week lies a good virus: the one that underlies gene therapy for X-linked severe combined immunodeficiency (SCID-X1),

Altered viruses are the vehicles that transfer healthy human genes into the cells of people in whom the genes aren’t working, providing a slew of new “forever fixes.” Nearly 100 gene transfer protocols are now in late-stage clinical trials. Read More 
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No Ice Buckets or Pink Ribbons for Very Rare Genetic Diseases

October 10, 2014
Tags: rare diseases, ice bucket challenge, Leber congenital amaurosis, Batten disease, giant axonal neuropathy, juvenile Huntington disease, ALS, breast cancer
As enthusiasm for dumping ice on one another fades with autumn and October brings pervasive pink, I wish that attention would turn to families confronting diseases not as well known as ALS and breast cancer.

HOW RARE IS RARE?
According to the National Organization for Rare Disorders, “rare disease” in the U.S. means affecting fewer than 200,000 people. These conditions number about 6,800, collectively affecting nearly 30 million Americans or 1 in 10 people.

Many are single-gene diseases. That means that the chance of more than one family member being affected is quite high (see Mendel's first law). Unlike those, most (>90%) cases of ALS and breast cancer aren’t inherited as single-gene traits, but are sporadic. Mutations happen during a person’s lifetime in somatic cells, perhaps due to an environmental trigger. A family with one member who has ALS wouldn't have as great a chance as it affecting another as a family with Huntington disease, for example.

With so many causes of rare diseases, comparing statistics is an apples-and-oranges exercise. But I collected a few anyway, for prevalence (the percentage of a population with a particular disease at a given time). Read More 
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DNA and Dating: Buyer Beware

September 28, 2014
Tags: DNA, genetic testing, DNA and dating
Is DNA dating destiny?
Last week’s post dealth with three very serious applications of DNA testing. But not all DNA testing is to detect health-threatening conditions.

“Born to Run? Little Ones Get Test for Sports Gene,” ran the headline on the front page of the New York Times, above an arresting image of a preschooler having his mouth swabbed for DNA. It’s from 2008, but remains a classic: I still assign it.

The sports gene company is apparently still around and still testing for variants in just one gene: ACTN3. Two copies of the R577X variant indicate inborn skill at endurance events, and no copies suggest a child stick to sprints. The lucky heterozygotes might excel at both! Never mind that a child has some 20,000 or so other genes affecting physiology.

DISSECTING A DNA DATING WEBSITE
The most damage a sports gene test can do is to keep a child from doing something she loves because of a DNA-obsessed parent. A more questionable application of DNA testing is as part of “relationship science,” something I learned about a few weeks ago when a reporter from healthline.com asked me about it. Read More 
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