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Genetic Linkage

Roan’s Story and Fragile X Syndrome

For 2019's Rare Disease Day, DNA Science honors those who have fragile X syndrome (FXS). It isn't among the rarest of the rare, yet when health care providers can't assemble the diagnostic puzzle pieces that parents are practically yelling at them, the statistics don't matter and the diagnostic odyssey lengthens. Because fragile X is an "expanding repeat" disorder, it lies beneath the radar of standard chromosome and single-gene tests.

 

The Orphan Drug Act of 1983 in the US defined a rare disease as affecting fewer than 200,000 people. "Orphan" initially referred to pharma's disinterest in developing drugs with minuscule markets, but was deemed non-PC and became "rare" somewhere along the way. In the European Union, the definition is fewer than 1 in 2,000 people, which is pretty close to the US number. The disinterest in seeking treatments for ultrarare conditions has evolved into doing so, but with sky-high price tags.

 

A few weeks ago I heard from Desiree Moffitt, who uses my human genetics textbook to teach an online course. She kindly offered to share her family's story about life with a child who has fragile X syndrome. "Usually the face of disability is a very happy, quirky family. While we are happy and also quirky, our story isn't as fun," she emailed me. First, some background on fragile X.

 

To continue reading go to my DNA Science blog at PLOS, where this post first appeared.

 

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10 Things Exome Sequencing Can't Do -- But Why It's Still Powerful

Clinically relevant information in DNA hides in repeats, controls, and "junk" -- not just the protein-encoding exome.
10 Things Exome Sequencing Can’t Do – But Why It’s Still Powerful

Sequencing of the exome – the protein-encoding parts of all the genes – is beginning to dominate the genetics journals as well as headlines, thanks to its ability to diagnose the formerly undiagnosable.

The 2011
Pulitzer Prize in Explanatory Reporting
honored the Milwaukee-Wisconsin Journal Sentinel’s coverage of a 4-year-old whose intestinal disorder was finally diagnosed after sequencing his exome.  Read More 
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Anticipation

Jordan and Hailey Kohl. Spinocerebellar ataxia type 2 affects several members of their family, including Jordan.
“Anticipation .. is keepin’ me waitin’,” sings Carly Simon in her song made famous in a ketchup commercial. But “anticipation” in the genetic sense is just the opposite of Carly’s croon – it means a disease that begins earlier with each generation.

Doctors once blamed patients for anticipation, as if people with sick older relatives could worry themselves into suffering similarly. Then, in 1991, discovery of a new type of mutation explained the curious worsening of fragile X syndrome: an expanding triplet repeat.  Read More 
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