Aplastic Anaemia, PNH and Myeloid Neoplasms with Germline Predisposition Flashcards
Discuss the pathogenesis of acquired/ autoimmune aplastic anaemia
- Cytotoxic T lymphocytes are central to the pathogenesis of AAA.
- These are activated in AAA and produce type 1 cytokines, induce apoptosis and circulate as oligoclones.
- They cause bone marrow aplasia through cytotoxicity/ apoptosis and cytokine mediated bone marrow suppression.
- While AA is primarily a immune mediated disorder, it is linked to clonal haematopoiesis with the majority of AA patients having detectable somatic mutations/ chromosomal abnormalities.
- Mutated clones are not necessarily malignant but confer a survival advantage as the CTLS are usually directed against normal HSCTs.
Discuss the types of mutations seen in acquired aplastic anaemia
1) Chromosomal abnormalities
- Del(7q), trisomy 8, del(13q) most common
2) Copy number neutral LOH in the MHC genes (6p)
3) PHN clones
- Seen in ~50% of AAA
- Correlates with the presence of PIGA mutations
4) Age related/ CHIP mutations
- ASXL1 and DNMT3A most common
5) Other mutations
- BCOR, BCORL1
- STAT3
What mutations are associated with a response to IST in acquired aplastic anaemia?
1) Chromosomal abnormalities
- trisomy 8, del(13q)
2) Presence of a PNH clone
3) Other mutations
- PIGA, BCOR, BCORL1
What mutations are associated with a poorer response to IST in acquired aplastic anaemia?
Del(7q)
ASXL1
(Both also associated with an increased risk of progression to MDS)
How can you distinguish between hypoplastic MDS and acquired aplastic anaemia
Difficult. Likely represent spectrums of same disease process with T cell mediated myelosuppression implicated in hypoplastic MDS and response to IST seen in up to 30% with hypoplastic MDS
- Dysplastic morphological features favour MDS
- Increased CD34 cells on IHC or flow favours MDS (should be low in AAA)
- Abnormal differentiation of CD34/ CD117 pos cells on flow cytometry
- Presence of MDS defining chromosomal abnormalities (with exception of del(7q))
- Complex karyotype favours MDS
- Presence of spliceosome mutations or multiple somatic mutations favours MDS
- Presence of CHIP mutations does not distinguish
What is the Camitta criteria for severe and very severe aplastic anaemia
Severe AA
1) Bone marrow cellularity <25% (or 25-50% with <30% residual haematopoietic cells)
2) 2/3 of the following
- Reticulocyte count <20
- Platelet count <20
- ANC <0.5
Very severe AA
As above although ANC <0.2
List the causes/ syndromes associated with inherited bone marrow failure
1) Disorders of telomere biology
- Dyskeratosis congenita
2) Disorders of DNA repair
- Fanconi anaemia
3) Disorders of ribosomal biosynthesis
- Diamond Blackfan Anaemia
- Shwachman Diamond Syndrome
4) Severe congenital neutropenia
5) Congenital amegakaryocytic thrombocytopenia
What is dyskeratosis congenita?
- Disorder of telomere maintenance and repair resulting in shortened telomere length
- X linked recessive disorder
- Classic clinical triad of abnormal skin pigmentation, nail dystrophy and leukoplakia of the oral mucosa
- Also have premature greying, testicular atrophy and increased risk of liver cirrhosis
- Bone marrow failure occurs in >80%
- Diagnosed with telomere length assessment: DKC patients will be <1st centile (Flow FISH assay)
- Confirmed with genetic testing (DKC1 in 40%, TERT, TERC). 40% have no identifiable genetic lesion.
What is Fanconi anaemia?
- Caused by mutations that result in an impaired ability to repair DNA damage via homologous recombination
- Short stature, cafe au lait spot, skeletal and urogenital abnormalities
- 30% do not have the characteristic physical features
- 80% develop BM failure by age 20
- Increased risk of AML and MDS
- Diagnosed using the chromosomal fragility test (PB lymphocytes or skin, cultured with a T cell mitogen to stimulate division, DNA cross linking agent added (mitomycin C), look for breakage and rearrangement.
- Mutational analysis (FANCA, FANCC and FANCG is >80%)
- SNP microarray
What are the three subcategories of the diagnosis of “myeloid malignancies with germline predisposition” and give examples of each
1) Myeloid malignancy with germline predisposition without pre-existing disorder or organ dysfunction
- CEPBA, DDX41
2) Myeloid malignancy with germline predisposition with-existing platelet disorder
- RUNX1, ANKRD2, ETV6
3) Myeloid malignancy with germline predisposition with other organ dysfunction
- IBMFS, telomere disorders, GATA2, JMML with NF1 or Noonans, Noonan syndrome-like disorders, Down Syndrome
Discuss DDX41
- On Chr5
- Involved in RNA metabolism
- Can be sporadic somatic or germline
- Mean age of MDS/AML in those with germline mutation: 62
- Progression to malignancy usually associated with an acquired/ somatic DDX41 mutation on the other allele
- Prognosis depends upon associated chromosomal abnormalities- poor with del(5q)
- Likely under-recognised. Important as can influence donor selection
Discuss GATA2
- On Chr3
- Transcription factor
- Autosomal dominant inheritance
- Broad phenotype (familial AML/ MDS, infection, MonoMac syndrome, Embergers syndrome, B and NK lymphopenia, warts, pulmonary alveolar proteinosis)
- FBC shows cytopenias, including monocytopenia and lymphopenia
- Hypocellularity and abnormal megakaryocytes of BMAT
- Acquired monosomy 7 and trisomy 8 on cytogenetics
- Acquired ASXL1
- Confirmed with genetic sequencing (be aware of false negatives)
Discuss RUNX1
- On chromosome 21
- Transcription factor (subunit of the core binding factor complex)
- Autosomal dominant inheritance
- Lifelong mild to moderate thrombocytopenia with mild bleeding tendency
- Mild platelet agg defect with collagen and epinephrine
- Lifetime risk of MDS/AML 35-40%
- Average age of diagnosis 33
How is PNH diagnosed
1) Evidence of non-immune mediated haemolysis
2) Evidence of a population of peripheral blood cells deficient in GPI-anchored proteins by routine flow cytometry analysis
(At least two different GPI linked proteins in two different cell lines needed to make diagnosis)
- Red cells identified by CD45 and CD235a characteristics. GPI linked proteins used: CD55 and/ or CD59
- Neutrophils identified by CD15 and side scatter characteristics. GPI linked proteins used: FLAER and CD66b
- Monocytes identified by CD33 and side scatter characteristics. GPI linked proteins used: FLAER and CD14
3) Bone marrow biopsy to determine if there is an underlying associated haematological disorder
What are the three different types of PNH
1) Classic PNH (Red cell haemolysis with release of free haemoglobin, NO depletion and thrombosis due to complement activation)
2) PNH associated with a haematological disorder (AA, MDS, PMF)
3) Subclinical PNH (clone present, no evidence of haemolysis)
