Tests in analytical validation
| Test | Condition | Repeat measured | Status |
|---|---|---|---|
| DMPK repeat expansion | Myotonic dystrophy type 1 (DM1) | CTG repeat in the 3′ untranslated region of DMPK | Analytical validation |
| TCF4 repeat expansion | Fuchs endothelial corneal dystrophy (FECD) | CTG18.1 repeat in intron 3 of TCF4 | Analytical validation |
Report contents and size bands
Each report will give both allele sizes and classify each allele against these size bands.
| Gene | Normal | Premutation | Expanded |
|---|---|---|---|
| DMPK | 34 repeats or fewer | 35 to 49 | 50 or more |
| TCF4 | 39 repeats or fewer | None | 40 or more |
An extended report adds the single-molecule profile of the expanded allele: its median length with a confidence interval, an estimate of the length inherited at conception (the progenitor allele), the full somatic distribution and any interruptions in the repeat.
In DM1 the expanded DMPK repeat keeps lengthening in blood cells over a lifetime, so the length a standard test reports from blood rises with age at sampling. The estimated length inherited at conception predicts age at onset better than that blood length.
Clinical inquiries
Physicians and genetic counselors who want to discuss the assays can write to Steven Oldenburg, PhD, at [email protected].
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