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Genetic Linkage

Rare Diseases: Unicorns, Not Zebras

The past and future of gene therapy: Corey Haas and Hannah Sames autograph books at the Schenectady Library.
“When you hear hoofbeats, think horses, not zebras.”

Every doctor-to-be hears this mantra. Rare Disease Day, February 28, celebrates the 7,000 or so diseases that are zebras, each affecting fewer than 200,000 people.

Giant axonal neuropathy (GAN) isn’t a zebra, but a unicorn. Eight-year-old Hannah Sames inherited one mutation from each of her parents in a gene that encodes a protein called gigaxonin. As a result, the axons of her motor neurons are slowly filling up with haphazardly-arrayed intermediate filaments. The cells bulge, blocking the messages to her muscles. She’s one of only 50 in the world known to have GAN. But if all goes according to schedule, Hannah and several other youngsters are going to have gene therapy to correct the disease. Read about it at Hannah’s Hope Fund.

Two years ago, at the annual meeting of the American Society of Gene and Cell Therapy in Washington, I had the honor of watching Hannah’s marvelous mom Lori as she watched a child helped by gene therapy – Corey Haas, whose story bookends a brief history of the technology in "The Forever Fix: Gene Therapy and the Boy Who Saved It".

Here’s an excerpt, for Rare Disease Day. Read More 
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New Guidelines on Testing Kids’ DNA – the Cliff’s Notes Version

Should kids have genetic tests? It depends. (NHGRI)
Exomes are big news. Sequencing of the protein-encoding part of the genome is increasingly solving medical mysteries in children. It began with Nicholas Volker and his recovery from a devastating gastrointestinal disease with a stem cell transplant once his exome sequence revealed his problem. And recent Medscape assignments reveal the trend: 7 of 12 kids’ exomes leading to diagnosis at
Duke University
from May 10, 2012; whole genomes of 5 infants from the neonatal intensive care unit at Children’s Mercy Hospital and Clinics in Kansas City, Missouri from October 3, in under 2 days each, focusing on 600 single-gene diseases; and 300 patients at the Whole Genome Laboratory at the Baylor College of Medicine, with 300 more waiting -- 85% of them kids, from November 9, 2012. (You have to sign in to Medscape; it’s free.)

But wait.

Before we all run out to get our exomes and/or genomes sequenced, Read More 
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Genetic Testing: Carrier Confusion & Generation Reversal

A breast cancer cell. (Natl Cancer Inst)
In the usual trajectory of passing on genetic information, the older tell the younger, when the time is right. Typically, a patient has a genetic test because family history, ethnic group, or some other clue suggests to an astute practitioner an increased risk of something specific.

If a test reveals a mutation that could cause a disease, then the patient and perhaps her partner discuss how, when and what to tell their children – in the best of circumstances, with the help of a genetic counselor. Read More 
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Another Bump in the Road for Gene Therapy?

Mercury can see, thanks to gene therapy. (Foundation for Retinal Research)
I am astonished, once again, by the complexity and unpredictability of science.

Last week, a paper in the Proceedings of the National Academy of Sciences (PNAS) reported that gene therapy to treat a form of blindness called Leber congenital amaurosis type 2 (LCA2) doesn’t stop degeneration of the rods and cones – the photoreceptor cells that provide vision. Gene therapy sends the genetic instructions for a protein called RPE65 into a layer of cells that supports the rods and cones – the retinal pigment epithelium, or RPE. The protein is essential for the eye to use vitamin A. And the gene therapy works, so far.  Read More 
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