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Genetic Linkage

Rare Disease Day 2017: Talia's Story

Talia Duff with Cynthia the Hippo
This year for Rare Disease Day – February 28th – DNA Science honors Cure CMT4J: Advancing Gene Therapy for Rare Diseases, run by Jocelyn and John Duff. Their daughter Talia’s “diagnostic odyssey” was unusually long because Down syndrome obscured a second condition, an extremely rare form of Charcot-Marie-Tooth (CMT) disease. Read More 
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Defying Mendelian Genetics and "Embryo Engineering"

(credit: Children's Mercy Kansas City)
Mendel’s laws, like any laws in science, make predictions possible. A woman and man both carry a recessive mutation in the same gene, and each of their children has a 25% chance of inheriting both mutations and the associated health condition.

In contrast to our bizarre new world of “alternate facts,” science is both logical and rational. If an observation seems to counter dogma, then we investigate and get to the truth. That’s what happened for Millie and Hannah, whose stories illustrate two ways that genetic disease can seem to veer from the predictions of Mendel’s first law: that genes segregate, one copy from each parent into sperm and ova, and reunite at fertilization. (I’ll get to embryo engineering at the end.)

Millie’s situation is increasingly common – exome or genome sequencing of a child-parent “trio” reveals a new (“de novo”), dominant mutation in the child, causing a disease that is genetic but not inherited.

Hannah’s situation is much rarer: inheriting a double dose of a mutation from one parent and no copies of the gene from the other. Read More 
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Pig People?

When Medscape asked me late last week to cover the making of early embryos that have cells from pigs and humans, I couldn’t help but flash back to the Pigman episode of Seinfeld. "The government's been experimenting with pig-men since the '50s!" warned a terrified Kramer after finding one such creature hidden on the top floor of a hospital.

We didn't see Kramer’s porcine/human chimera of the 1990s, but a 1960 episode of the Twilight Zone, The Eye of the Beholder, provides an earlier illustration of the mixing of the species. Read More 
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