Fast Five Quiz: Inherited Conditions

Germaine L. Defendi, MD

Disclosures

October 29, 2018

The prenatal tests chorionic villus sampling and amniocentesis for SCD are available. Both are sensitive and rapid options. Chorionic villus sampling is performed at 10-13 weeks' gestation to obtain chorionic villi tissue for DNA analysis, whereas amniocentesis obtains a sample of amniotic fluid and is performed later, at 15 to 18 weeks' gestation. Both procedures are safe; however, a low risk for miscarriage and/or infection is noted. Postnatal newborn screening for hemoglobin S (HbS) is currently mandatory in the United States. Typically, newborn screening for HbS and many other diseases is done 24-48 hours after a baby's birth by placing a few drops of blood from a heel stick onto a filter-paper card. Today, newborn screening is standard of care in the United States and allows for implementation of early diagnostic treatment.

Individuals with SCD present with a wide range of clinical problems that result from vascular obstruction and ischemia. Clinical manifestations include recurrent pain crises and progressive incremental infarction. Although SCD can be diagnosed at birth, clinical concerns usually do not arise before age 6 months, when functional asplenia develops. Functional asplenia causes susceptibility to infection by encapsulated bacteria. Subsequently, sepsis can cause additional organ system damage. Treatment for functional asplenia is daily oral penicillin or amoxicillin in children younger than 5 years and for at least 1 year after splenectomy.

Splenic sequestration refers to an acute intrasplenic pooling of large amounts of blood. Children with SCD aged 5 months to 2 years represent most cases, with most incidents occurring within the first 5 years of life. During severe sequestration crisis, the blood-filled spleen may enlarge to fill the abdominal space. Onset of life-threatening anemia occurs. Hypovolemic shock ensues, and death may occur within hours of onset. Prompt treatment with volume expanders and blood transfusion to reverse the hypovolemic shock can help remobilize the blood sequestered in the spleen and lead to regression of the splenomegaly.

Deferoxamine (Desferal) is an efficient iron chelator for the treatment of chronic iron overload from recurrent blood transfusions. This chelator can be administered intramuscularly or as a prolonged infusion, either intravenously or subcutaneously. Deferasirox and deferiprone, both oral iron chelators, are also effective for iron overload treatment. Deferasirox has a capacity similar to deferoxamine in chelating iron but is administered orally. Renal toxicity might be a limiting factor in its use, but it is generally safe. Deferiprone does not seem to be as effective a chelator as these other two medications and is considered a second-line therapy. Unlike deferasirox and deferoxamine, deferiprone selectively removes cardiac iron and is most effective when used in combination with deferoxamine or deferasirox.

For more information on SCD, read here.

 

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