Better, Cheaper Assay for Fragile X Syndrome Detection

MedicalResearch.com Interview with:

Karen Usdin, Ph. D. Senior Investigator Chief, Gene Structure and Disease Section Laboratory of Cell and Molecular Biology National Institute of Diabetes, Digestive and Kidney Diseases National Institutes of Health Bethesda MD 20892

Dr. Karen Usdin

Karen Usdin, Ph. D.
Senior Investigator
Chief, Gene Structure and Disease Section
Laboratory of Cell and Molecular Biology
National Institute of Diabetes, Digestive and Kidney Diseases
National Institutes of Health
Bethesda MD 20892

MedicalResearch.com: What is the background for this study? What are the main findings?

Response: Our laboratory is interested in the causes and consequences of the unusual repeat expansion mutation that causes the Fragile X-related disorders. However these disorders are challenging to study, in part because the repeat tract is difficult to amplify by PCR. This makes monitoring of repeat length, as well as other factors we are interested in such as methylation status and the presence of AGG interruptions, quite difficult.

In our experience, both repeat number and methylation status are very variable in patient stem cells and in disease-relevant cell types derived from them. This variability arises because the repeat is prone to both expansion and contraction and because at different times there can be selection for smaller alleles or against unmethylated ones. Thus the frequent monitoring of repeat length and methylation status is critical for work with patient cells, particularly when those cells are to be used for drug screening or to examine the consequences of expansion.

While other assays are available to determine one or more of these parameters, some are cumbersome to use or lack the necessary robustness and sensitivity, whilst others are prohibitively expensive for routine laboratory work. We thus saw a need for assays that are robust, sensitive and cost-effective for preclinical studies.

MedicalResearch.com: What should readers take away from your report?

Response: We have developed a relatively inexpensive set of assays that can be used to monitor, on a routine basis, the repeat length, AGG interruption status and the extent of DNA methylation in patient-derived cells. While primarily intended as a tool for preclinical studies, in principle, these assays could also be developed for use in a diagnostic setting perhaps as a prelude or adjunct to the more expensive commercially available assays or ultimately as part of a new born screening panel. Of particular interest for diagnostics may be our assay for the number of uninterrupted repeats at the 3’ end of the repeat tract. Our assay allows this important determinant of expansion risk to be readily assessed even in women with large premutation alleles. This information is sometimes difficult to obtain with existing assays, but is particularly important for these women since it affects their risk of having a child with Fragile X syndrome.

MedicalResearch.com: What recommendations do you have for future research as a result of this study?

Response: Since patient-derived stem cells and cells derived from them are prone to selection for different allele sizes and methylation states, it is critical to monitor these parameters frequently. Our assays mean that there should no longer be either a technical or financial barrier to doing this. Our recommendation is that these parameters be monitored on an ongoing basis to avoid experimental artifacts and misinterpretation of data.

MedicalResearch.com: Thank you for your contribution to the MedicalResearch.com community.

Citation:

A Set of Assays for the Comprehensive Analysis of FMR1 Alleles in the Fragile X-Related Disorders, by Bruce E. Hayward, Yifan Zhou, Daman Kumari and Karen Usdin (doi:10.1016/j.jmoldx.2016.06.001). It appears in The Journal of Molecular Diagnostics, volume 18, issue 5 (2016),

Note: Content is Not intended as medical advice. Please consult your health care provider regarding your specific medical condition and questions.

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