As a true recessive trait, CFTR mutations in heterozygos-ity are silent and asymptomatic, and because even their sweat chlorides are entirely normal, CF carriers are unidentifiable unless they have produced an affected child or have undergone mutation testing. Obviously, anyone of reproductive age who has a positive family history of the disease is considered a candidate for carrier testing. But because most CF carriers have negative family histories and only find out they are carriers after the birth of their first affected child, screening of the entire reproductive population has long been discussed as a preventative, public health measure. This is justified because of the high carrier frequency in the general populations of North America and northern Europe. Under current recommendations,1-5-1 couples who are pregnant or contemplating pregnancy are offered DNA-based carrier screening with a standard panel of the 25 most prevalent CFTR mutations. If both members are found to be carriers of identifiable CFTR mutations, they are referred for genetic counseling to inform them of their 25% risk of producing an affected child and to discuss the options for pregnancy termination. Naturally, such discussions are conducted in a nondirec-tive and noncoercive manner, with full disclosure about the variability of CF symptoms and the uncertain geno-type-phenotype correlations.
Couples with a positive family history should ideally first seek mutation testing of the affected index case. If one or both CFTR mutations are not detected with the core 25-mutation panel, the case may be referred for extended panel testing or even complete CFTR gene sequencing.
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The use of dumbbells gives you a much more comprehensive strengthening effect because the workout engages your stabilizer muscles, in addition to the muscle you may be pin-pointing. Without all of the belts and artificial stabilizers of a machine, you also engage your core muscles, which are your body's natural stabilizers.