Hemoglobin SC disease

Radiopaedia • CC-by-nc-sa 3.0 • de

Hemoglobin SC (HbSC) disease is a hemoglobinopathy, and a common variant of sickle cell disease (SCD). There is coinheritance of one HbS gene and one HbC gene, resulting in a milder phenotype than full-blown sickle cell disease. It most commonly manifests with a proliferative retinopathy. Painful crises, functional asplenia and osteonecrosis are also frequent sequelae.

Epidemiology

Hemoglobin SC disease makes up almost 30% of cases of sickle cell disease in the United Kingdom and the United States . In some regions of West Africa, where the HbC variant arose, HbSC may form more than half of all cases of sickle cell disease . Globally more than 50,000 babies with HbSC are born each year.

Clinical presentation

In general, hemoglobin SC disease is viewed as a milder variant of sickle cell disease, nevertheless significant morbidity still often results.

  • ocular: proliferative retinopathy commonest complication of HbSC, ~70%
  • painful crises are common, seen in half of patients
  • splenic: functional asplenia in 45% by the age of 12 years
  • bone: osteonecrosis affects almost one quarter of HbSC patients
  • CNS: strokes
  • priapism: ​20% of male patients develop this sequela
  • acute and chronic lung disease
  • thromboembolism: PE and DVT are more common
  • renal
  • gallbladder disease in 20% (cf. sickle cell disease 50%)

Pathology

Genetics

Inheritance of the hemoglobin S (HbS) and hemoglobin C (HbC) beta globin gene (HBB) mutations together (i.e. coinheritance) results in hemoglobin SC (HbSC) disease.