Tetrameric hemoglobin consists of two different globin chain pairs, each containing one heme molecule. Balanced expression of a-globin and non-a-globin chains is necessary for normal hemoglobin synthesis and RBC function. During development, three embryonic hemoglobins are produced: Hb Gower-1 (Z2/e2), Hb Gower-2 (a2/e2), and Hb Portland (a2/g2). By week 8, fetal hemoglobin (HbF, a2/g2) comprises at least 50% of the hemoglobin present. A 8- to p-globin chain switch by 12-16 weeks after birth results in a shift to the predominant adult hemoglobin, HbA (a2/p2). This phenomenon of postnatal hemoglobin switching precludes clinical consequences of p-globin chain variants before or at the time of birth. Individuals with clinically significant hemoglobin variants, and those that produce disease when coinherited with a- or p-thalassemias, tend to become symptomatic only after the decline in HbF levels after the first months.

Diagnostic testing for hemoglobinopathies generally is performed for clinical evaluation and population (newborn) screening. In couples considering pregnancy, pregnant women, or conceptuses, laboratory evaluation for hemoglobinopathies can confirm a provisional diagnosis, e.g., SCD, determine the cause(s) of a hematological abnormality, e.g., anemia or microcytosis, permit genetic counseling for prospective parents, or make a fetal diagnosis.

Getting Started With Dumbbells

Getting Started With Dumbbells

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.

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