HAEMATOLOGY EQA
Learning from external quality assessment: a case of Hb Knossos
Education is an important aspect of the services provided by UK NEQAS schemes operating across laboratory medicine. Here, Bashori Rahman and Barbara De la Salle provide an example using a rare haemoglobin variant circulated as part of their molecular EQA scheme.
The UK NEQAS Haematology scheme supplies a comprehensive range of external quality assessment (EQA) programmes designed to support the quality assurance needs of participating laboratories.
The DNA Diagnostics for Haemoglobinopathies (DN) EQA programme supports specialist laboratories that offer molecular haemoglobinopathy testing as part of their diagnostic repertoire. It is designed to performance assess how laboratories identify mutations of the alpha- and beta-globin genes, and the interpretation of the results obtained in the context of the patient’s clinical background and other haematology.
Assay material is supplied as DNA in Tris-EDTA (TE) buffer and is suitable for all molecular haemoglobinopathy techniques. Each specimen is supplied with clinical case details, gender and ethnic background, and haematology results.
Structure of human haemoglobin showing alpha- and beta-globin subunits in red and blue, respectively, and the iron-containing heme groups in green.
28 Background
Hb Knossos is a haemoglobin variant caused by a mutation in codon 27 that changes the amino acid alanine to serine. This mutation has been identified in multiple individuals with origins in the Mediterranean basin, including North African countries. In addition to creating an Hb variant protein, this mutation activates a cryptic splice site, resulting in many of the transcripts being degraded; therefore, the variant has a relatively lower
expression than a normal beta-globin chain and acts as a beta+ thalassaemia mutation (the variant is still functional to some degree). Hb Knossos migrates with Hb A using most methods of haemoglobin separation, so the variant peak is not obvious in heterozygotes. This mutation is typically identified in cis with a delta zero thalassaemia mutation (HBD c.179delA), causing the detectable Hb A2 to be reduced by around 50%. This means that in the heterozygous state it is associated with an Hb A2 of 1.8–2.4%, and in the homozygous state there is no Hb A2 present at all.
A DNA specimen from a child with this mutation was used in a UK NEQAS exercise in November 2022 (distribution 2203DN). This particular child was heterozygous for Hb Knossos and the delta zero thalassaemia mutation (HBD c.179delA). They were also compound heterozygous for alpha+ thalassaemia due to the 3.7 kb alpha+ deletion and a non-deletional IVS1(- 5nt) mutation.
The clinical details stated that the child is of Moroccan origin with microcytic anaemia, with normal high-performance liquid chromatography (HPLC), and that his father has beta- thalassaemia intermedia.
Methodology A total of 48 laboratories participated in this survey. Participants were asked to test the specimen as per their usual diagnostic workflow for an ordinary patient specimen for both alpha- and beta-globin genotyping. Gamma
FEBRUARY 2024
WWW.PATHOLOGYINPRACTICE.COM
Zephyris CC BY-SA 3.0 Wikimedia Commons
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56
