Final answer:
SCD symptoms typically manifest at around 6 months of age due to the replacement of fetal hemoglobin with sickle hemoglobin, leading to red blood cells sickling and associated complications like anemia.
Step-by-step explanation:
Patients with Sickle Cell Disease (SCD) usually do not exhibit symptoms until 6 months of age because fetal hemoglobin (HbF) is present in their blood during this time. Newborns have a high concentration of HbF, which does not sickle under low oxygen conditions, in contrast to sickle hemoglobin (HbS) that arises in SCD. Symptoms begin to appear as the level of fetal hemoglobin decreases and is replaced by HbS, leading to sickling of red blood cells and the associated complications of SCD such as anemia and other physiological changes. These complications include symptoms such as physical exertion, weakness, shortness of breath, and potential heart murmurs.