Genomics in general practice

Haemoglobinopathies

Genomics in general practice
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  1. Summary of genetic testing
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Last revised: 30 Nov 2018

Practice point

General practitioners (GPs) play an important role in identifying potential carriers of haemoglobinopathy. They also play an important role in identifying couples who are at risk of having a child with a haemoglobinopathy.

Carrier screening should be discussed with couples who are potential carriers of haemoglobinopathy because of their ethnicity, and are planning pregnancy or in the first trimester of pregnancy.1

To enable timely reproductive choices during early pregnancy, carrier screening should be offered to couples at the same time (ie both partners should be tested as early as possible).
 

The term ‘haemoglobinopathies’ covers a range of conditions with an autosomal recessive inheritance pattern that affect haemoglobin, including α-thalassaemia and β-thalassaemia, sickle cell disease and other abnormal haemoglobins, such as haemoglobin E (HbE).

Individuals with thalassaemia produce insufficient haemoglobin, while those with sickle cell disease produce structurally abnormal haemoglobin. The clinical implications range from mild through to death in utero.

Collectively, haemoglobinopathies are the most common single gene disorders in humans, and around 7% of the world’s population are carriers.1 Haemoglobinopathies are becoming more prevalent in Australia given immigration from endemic regions.2

While carriers are often asymptomatic, carrier status becomes clinically significant in women who are carriers and planning a pregnancy, where the biological male partner is also a carrier.1 Screening for haemoglobinopathies is not part of the newborn screening program in Australia.

Carrier screening should be discussed as part of pre-pregnancy and prenatal care in the following individuals:1–4

  • Those with family history of anaemia or haemoglobinopathy.
  • Those from the following ethnic backgrounds (have increased carrier frequency)
  • southern European
  • African
  • Middle Eastern
  • Chinese
  • Indian subcontinent
  • central and south-east Asian
  • Pacific Islander
  • New Zealand Maori
  • South American
  • Caribbean
  • some northern Western Australian and Northern Territory Aboriginal and Torres Strait Islander communities.
  • Those with a mean corpuscular volume (MCV) <80 fL or mean corpuscular haemoglobin (MCH) <27 pg.
  • Biological male partners of known female carriers.

Order a haemoglobinopathy screen to include:1,2,4

  • full blood examination (FBE) for MCV and MCH
  • ferritin to exclude iron deficiency
  • haemoglobin electrophoresis
  • deoxyribonucleic acid (DNA) testing if indicated (Table 1).

There is an urgency to test the biological male partner concurrently when an at-risk woman who is a carrier is pregnant. DNA testing is required when α-thalassaemia cannot be excluded and the partner is a known carrier of two-gene deletion α-thalassaemia (Table 1).

Table 1. Interpretation of haemoglobinopathy carrier testing results

Table 1

Interpretation of haemoglobinopathy carrier testing results2

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HbA2 , normal variant of haemoglobin with two α-globin and two β-globin chains; HbE, abnormal variant of haemoglobin, due to abnormal β-globin; HbH, abnormal variant of haemoglobin, due to excess β-globin chains relative to β-globin chains, a type of α-thalassaemia; HbS, abnormal variant of haemoglobin, due to abnormal β-globin; MCH, mean corpuscular haemoglobin; MCV, mean corpuscular volume.

Adapted from Metcalfe SA, Barlow-Stewart K, Campbell J, Emery J. Genetics and blood – Haemoglobinopathies and clotting disorders. Aust Fam Physician 2007;36(10):812–19.

Do not assume low MCV or MCH is due to iron deficiency alone, especially in at-risk individuals.1 If the patient is not pregnant, treat for the iron deficiency then retest. If MCV or MCH remain low, the individual is possibly a carrier of a haemoglobinopathy. If the patient is pregnant, DNA testing for α-thalassaemia is indicated.1

A woman only needs to have haemoglobinopathy screening once – if MCV or MCH is low but was previously normal, it is most likely due to iron deficiency.

Bender MA, Douthitt Seibel G, Sickle cell disease
Origa R, Moi P, Alpha-thalassemia
Origa R, Beta-thalassemia

Centre for Genetics Education, Fact sheet 43: Thalassaemia
Centre for Genetics Education, Fact sheet 44: Sickle cell disease
National Library of Medicine (US), Alpha thalassemia
National Library of Medicine (US), Beta thalassemia
National Library of Medicine (US), Sickle cell disease

  1. Tan YL, Kidson-Gerber G. Antenatal haemoglobinopathy screening in Australia. Med J Aust 2016;204(6):226–30.
  2. Metcalfe SA, Barlow-Stewart K, Campbell J, Emery J. Genetics and blood: Haemoglobinopathies and clotting disorders. Aust Fam Physician 2007;36(10):812–19.
  3. The Royal Australian and New Zealand College of Obstetricians and Gynaecologists. Prenatal screening and diagnosis of chromosomal and genetic conditions in the fetus in pregnancy (C-Obs 59). Sydney: RANZCOG, 2015 [Accessed 20 December 2017].
  4. The Royal Australian College of General Practitioners. Guidelines for preventive activities in general practice. 9th edn. Melbourne: RACGP, 2016 [Accessed 20 December 2017].
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