5 missense variants (Y89C, R96W, G134E, C140R, and H155Y) in or near IKZF5 zinc fingers in patients with isolated thrombocytopenia identified by WES (all absent from gnomAD v4) - 0.1*5 = 0.5 pts
PMID: 32419556
Identified c.355T>C (p.Ser119Pro) variant in a proband with with severe bleeding tendency and lifelong thrombocytopenia (absent from gnomAD v4) - 0.1 pt
Identified c.48G>C (p.Gln16His) variant in another proband (from a different family) with thrombocytopenia (absent from gnomAD v4) - 0.1 pt
ClinVar:
c.296_300delinsTGTGGATT (p.Glu99_His100delinsValTrpIle) seen in patient with Thrombocytopenia 7 (submitted by Baylor Genetics, absent from gnomAD v4) - 0.1 pt
Segregation Evidence:
PMID: 31217188
H155Y and C140R were de novo - 1 pt for segregation
G134E seen in 4 affected family members and 1 unaffected family member (LOD score: 1.505) - 0 pts for segregation
R96W segregated in 6 affected family members (LOD score: 1.806) - 0 pts for segregation
Y89C segregated in 2 affected family members (LOD score: 0.602) - 0 pts for segregation
Case/Control Evidence:
Experimental Evidence:
PMID: 31217188
In contrast to WT IKZF5, which enters the nucleus to bind to chromatin, all 5 causal mutants exhibited a strong reduction in chromatin binding, remaining instead in the cytosol and soluble membranes fractions - 0.5 pts (functional data)
Quantified proplatelet formation (PPF) after MK spreading on fibrinogen and staining with VWF and found it to be significantly reduced in 7 cases from 3 pedigrees compared with 6 unrelated healthy controls - 0.5 pts (functional data)
RNA sequencing revealed that platelet transcriptome of members from 3 pedigrees was different from controls. In particular, genes linked to platelet formation and function were deregulated and this explains thrombocytopenia and reduced platelet alpha-granules - 0.5 pts (functional data)
PMID: 32419556
In the proband with the p.Ser119Pro variant, light microscopy demonstrated unusual platelet morphology (platelets were elongated and often presented as proplatelets with 3–5 platelets still aligned connected by a cytoplasmic bridge). Flow cytometry analysis of the proband’s platelets demonstrated reduced size scatter indicating small platelet size - 0.5 pts (functional data)
In the proband with the p.Gln16His variant, light microscopy demonstrated platelets of variable size and shape. Platelets were elongated, sometimes resembling pro-platelets - 0.5 pts (functional data)
PMID: 10978333
IKZF5 is expressed in peripheral blood leukocytes, MEG-01 and M07e cell lines (megakaryocytic cell lines) - 1 pt