Clinical implications of a genetic test result showing the Hb C variant

Hb C disease is an autosomal recessive disorder; individuals with biallelic Hb C variants or compound heterozygosity for Hb C and a beta thalassemia variant that reduces production of normal beta chains will have a form of chronic hemolytic anemia. Hb C heterozygotes have an asymptomatic carrier state. Compound heterozygosity for Hb C and Hb S causes Hb SC, a form of sickle cell disease. If any individual has vaso-occlusive pain, they likely carry the Hb S variant. Refer to UpToDate for details.

* The three most common scenarios are listed. If a different HBB variant is present, discussion with hematology is appropriate to determine the implications and appropriate interventions. There are rare variants that have Hb C in their name but have a different genetic change and different significance. Hb C Harlem was initially labeled as a type of Hb C because it migrates in the same position as Hb on alkaline gel electrophoresis. However, it has a distinctly different genetic sequence; it contains the sickle cell mutation (p.glu7val; c.20A>T) plus an additional mutation at amino acid 73 (p.asp73asn; c.220G>A). Hb C Harlem can polymerize in the same fashion as Hb S.

¶ Ideally, reproductive counseling is done prior to conception.

Δ Evaluations and monitoring for individuals with sickle cell disease are extensive. Manifestations in Hb SC disease may be less severe than in Hb SS or Hb S-beta⁰ thalassemia, but there is significant variability. Refer to UpToDate for details.

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Clinical implications of a genetic test result showing the Hb C variant