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    The promise and peril of new prenatal diagnostic technologies

     

    Expanded carrier testing

    Similar challenges exist as we begin to grapple with the complexities of expanded parental carrier testing. Traditionally, such testing has been very limited and focused on conditions with a specific ethnic and racial predilection (eg, Tay-Sachs and sickle cell screening). However, the United States is now a multiethnic, multiracial society and increasingly couples have many ethnicities and racial admixtures, often unbeknownst to them.3 For example, my grandson has Swedish, Norwegian, German, Irish, English, Welsh, Scottish, Scotch-Irish, Catalan, Spanish, French, Northern and Southern Italian, and Corsican ancestors!

    Moreover, even among a given ethnic group, the number of diseases that can be tested for has expanded exponentially. Among the conditions that are often recommended to be screened for in couples of Ashkenazi Jewish ancestry are Tay-Sachs, Niemann-Pick A, Bloom syndrome, Canavan disease, familial dysautonomia, Fanconi anemia, Gaucher disease, mucolipidosis type IV, glycogen storage disease type 1a, maple syrup urine disease, nonsyndromic sensorineural hearing loss, and glycogen storage disease type III. However, even though Ashkenazi Jews are the most common carriers of Tay-Sachs disease alleles, because screening of such self-identified couples is so well utilized, most children affected by Tay-Sachs are not born to couples who identify themselves as Jewish.4 Thus, experts increasingly are urging pan-ethnic screening for many such disorders.

    Expanded carrier testing using high-throughput sequencing, similar to that used for cfDNA testing, can simultaneously screen for a large number of parental carrier states at relatively low cost. While traditional carrier testing is focused on relatively common, clearly defined, severe and/or lethal autosomal-recessive and X-linked recessive conditions, expanded carrier testing panels often include conditions with far more variable phenotypes, such as Fragile X and hemochromatosis, or those that are far rarer. Paradoxically, amongst the latter conditions, calculation of residual risk is often impossible.5 The use of high throughput sequencing has the added complexity of identifying both pathological and potentially benign genetic variants, making post-test counseling more difficult. Conversely, such testing may uncover risks for severe or fatal conditions in the parent, including diseases that present later in life and for which there is no current prevention, such as Huntington’s, Parkinson’s, and Alzheimer’s diseases. Finally, while such expanded testing is now widely available, professional society recommendations have generally not kept pace with the proliferation of these tests. Moreover, some still propose limiting carrier testing to certain ethnic groups while others recommend pan-ethnic screening for all the reasons cited above.

     

    Charles J. Lockwood, MD, MHCM
    Dr. Lockwood, Editor-in-Chief, is Dean of the Morsani College of Medicine and Senior Vice President of USF Health, University of South ...

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