ttenuating KLF1 activity to raise HbF levels in patients
with β-type hemoglobinopathies remains to be deter-
mined. Related to this, we have only begun to understand
the phenotypes associated with the different KLF1 muta-
tions, and more in-depth analyses might very well reveal
that there is significantly more overlap between these phe-
notypes than currently appreciated (Figure 3). The impact
of missense mutations on the phenotypic outcome also
warrants further investigation. For instance, missense
mutations of critical residues in the zinc finger domains of
KLF1 affect its DNA binding properties and may have a
dominant phenotype, as exemplified by the p.E325K muta-
tion in the CDA patients
and the p.E339D mutation in the
In contrast, the p.K332Q mutation, which
also affects the DNA binding properties of KLF1, does not
have a dominant effect.
Genome-wide assessment of the
in vivo binding sites of these mutant KLF1 proteins may help
to understand the phenotypic variability. In addition, it
appears that some target genes, such as BCL11A, EPB4.9
and CD44, are very sensitive to perturbations in KLF1 activ-
ity, while the effects on others, such as BCAM and γ-globin,
are much more variable. Studies in the Nan mouse indicate
that this might depend on the class of KLF1 binding site
responsible for activation of KLF1 target genes.
tion, modifier genes may affect the expression of the “vari-
able response” genes, as exemplified by the intricate inter-
play of KLF1 and BCL11A on γ-globin expression.
Identifying these modifier genes and characterizing the
molecular properties of KLF1 mutants are important chal-
lenges for further research. In addition, we expect that
many novel cases of individuals with KLF1 mutations will
be discovered in the near future. Novel mutations may pro-
vide insight into the functional domains of KLF1. Most of
the reported mutations affect the DNA binding domain
(Figures 1 and 3). KLF1 is known to interact with co-factors
such as the chromatin remodeling SWI/SNF complex, and
it undergoes post-translational modifications such as phos-
phorylation, acetylation and SUMOylation (M Siatecka
and JJ Bieker, submitted manuscript, 2011). Mutations
affecting these biochemical properties may provide impor-
tant clues to the functional roles of protein-protein interac-
tions and post-translational modifications. Furthermore,
given the broad impact of KLF1 on erythroid-specific gene
expression in the mouse,
the array of human erythroid
phenotypes associated with KLF1 mutations will likely be
expanded as more cases are described in detail. We note
that mutations without an obvious phenotype are equally
important to report, but difficult to publish in the peer-
reviewed literature. To keep track of all KLF1 mutations
and associated phenotypes, we have implemented the
and initiated a collaborative
effort for functional analysis of KLF1 mutants
(http://www.ithanet.eu/eklf-klf1). We strongly call upon
the hematology community to participate in these initia-
tives, to ensure that valuable information on KLF1 muta-
tions is systematically collected and accessible to both clin-
ical and research scientists.
Acknowledgments: this work has been supported by institution-
al funding of the University of Malta, and the Malta Department
of Health (AEF and JB), a fellowship of the Malta Government
Scholarship Scheme (JB), European Commission grants
GEN2PHEN; FP7-200754 and ITHANET; FP6-026539) to
GPP, and the Netherlands Genomics Initiative (NGI), Erasmus
MC (MRace; 296088), the Landsteiner Foundation for Blood
Transfusion Research (LSBR; 1040), and the Dutch organization
for scientific research (NWO; DN 82-301 and 40-00812-98-
08032) to SP. We apologize to our colleagues whose work could
not be cited due to space constraints.
Joseph Borg is an academic staff member of the University of
Malta, Faculty of Health Sciences, Department of Applied
Biomedical Science, and a researcher on the Thalassaemia
Project in the Laboratory of Molecular Genetics. George P.
Patrinos is Assistant Professor of Pharmacogenomics at the
University of Patras, Department of Pharmacy. He has been
involved in globin gene regulation research for over 15 years. His
research interests include pharmacogenomics of fetal hemoglobin
augmenting agents. Alex. E. Felice is the founder of the
Thalassaemia Project at the University of Malta where he is
Professor, and the Malta Department of Health, Mater Dei
Hospital where he is Visiting Consultant. His interests are in
hemoglobin epidemiology and globin gene control. Sjaak
Philipsen is Professor of Genomics of Cell Differentiation at the
Department of Cell Biology in Erasmus University Medical
Center in Rotterdam. His main research interest is how tran-
scription factor networks control erythropoiesis.
Financial and other disclosures provided by the author using the
ICMJE (www.icmje.org) Uniform Format for Disclosure of
Competing Interests are available with the full text of this paper at
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