Genomics in general practice


Haemoglobinopathies
☰ Table of contents


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).



What do I need to know?


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.
 

Genetic testing


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 results2

MCH (pg)/MCV (fL)

Ferritin

Haemoglobin electrophoresis

Interpretation

MCH <27 and/or MCV <80

Normal

HbA2 increased

β-thalassaemia carrier

HbA2 normal
HbH present

α-thalassaemia carrier

HbA2 normal
HbH high

Possible HbH α-thalassaemia

HbA2 normal
HbE present

HbE carrier or homozygote

Normal

Possible α-thalassaemia carrier; DNA testing indicated

Low

Normal

Iron deficiency

Thalassaemia may co-exist (treat iron deficiency then retest)

If woman is pregnant, seek advice about further tests

MCH ≥27 and/or MCV ≥80

Normal

Normal

Thalassaemia unlikely but one-gene deletion α-thalassaemia not excluded; DNA testing indicated only if partner is carrier of α-thalassaemia

Normal

HbS present

Carrier for sickle cell disease

Low

Normal

Reduced iron stores or iron deficiency, thalassaemia unlikely but one-gene deletion α-thalassaemia not excluded. Treat iron deficiency then retest

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.

 


When should I refer?


Urgent referral should be made to genetics or haematology services when carrier couples are identified during pregnancy in order to allow for timely reproductive decisions, or when a pregnant woman is identified as a carrier and of testing the biological male partner has not been done.

Urgent referral should be made to haematology services if a pregnant woman is found to have abnormal variant of haemoglobin (HbH) α-thalassaemia.

 


Other considerations


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.


Resources for general practitioners


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


Resources for patients


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


Genomics in general practice




 

 

  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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