Download (STEM CELL FACTOR RECEPTOR) GENE

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2497
CORRESPONDENCE
LACK OF APPARENT HEMATOLOGIC ABNORMALITIES IN HUMAN PATIENTS WITH c-kit (STEM CELL
FACTOR RECEPTOR) GENE MUTATIONS
To the Editor:
Considerable attention has recently been paid to the molecular
biology, cell biology, and mutations of the mouse Steel (SI) and
dominant white spotting (W;c-kit) loci, which respectively encode
stem cell
(SCF; also referred to as mast cell growth
and kit ligand7-9)and its cognate cellular receptor tyrosine
kinase.’O Mice with mutations at either of these loci have similar
developmental defects of the melanocyte, pre-erythroid, and germ
cell lineages. In addition to characteristic pigmentary anomalies
(white spotting), affected mice exhibit a hypoplastic macrocytic
anemia. Ten of 24 murine W mutant c-kit alleles result in anemia
even in the heterozygote, and virtually all W alleles result in
profound (often lethal) anemia in the homozygote.11-12
Recently, we have shown that human c-kit gene mutations result
in piebaldi~m,’~J~
a well-known autosomal dominant genetic disorder characterized only by white spotting. Human piebaldism was
one of the first genetic disorders ever recognized, and has never
been associated with anemia. Specifically, hematologic abnormalities were not described in any of 42 unrelated probands with
heterozygous piebaldism reported since 1950. Table 1 shows
hematologic data of six additional patients with heterozygous
piebaldism in whom we have defined specific c-kit gene mutations;
all values were within the normal ranges for the respective
laboratories. In addition, the hematologic values of a previously
reported patient with apparent homozygous autosomal dominant
piebaldi~m’~
were also entirely normal (M. Hulten, personal
communication, September 1991), although his c-kit genes have
not yet been analyzed.
The c-kit gene is expressed in human erythroleukemia cell
lines,I6and recombinant human SCF enhances the in vitro proliferative response of cultured human marrow cells to other growth
factors, including interleukin-3 (IL-3), granulocyte-macrophage
colony-stimulating factor, and erythropoietin (EPo).’~ Moreover,
c-kit antisense oligonucleotides inhibit both (IL-3 + Epo)- and
(SCF + Epo)-stimulated human erythroid colony proliferation in
vitro.’* All of these data are consistent with a role for c-kit in
human erythropoiesis. How, then, might the lack of apparent
hematologic abnormalities in patients with piebaldism be explained?
One trivial possibility is that many mutant human c-kit alleles do
result in significant anemia in the heterozygote, but these alleles
have just not yet been observed. The two human c-kit frameshifts
that we have described14 result in “null” alleles, and thus are
Table 1. Hematologic Findings in PatientsWith Piebaldism
Patient
RBC
Hb
Hct
MCV
MCH
MCHC
Sex
c-kit Mutation
1
2
3
4
5
6
5.08
4.43
4.46
3.96
3.70
4.92
15.3
13.7
13.3
13.0
12.1
14.6
45.7
40.5
39.8
ND
35.2
42.4
90.0
91.4
89.3
96.0
95.2
86.1
30.1
30.9
29.8
32.6
32.7
29.7
33.5
33.8
33.4
33.3
34.4
34.5
M
F
F
664Gly + Arg
664Gly --* Arg
664Gly + Arg
584Phe -+ Leu
642FS
561FS
F
F
M
~~~~~~~
Patients 1,2. and 3 are all members of one large kindred. Patients 4,5, and 6 are unrelated. All patients were white adult.
Abbreviations: RBC, red blood cells (RBChL); Hb, hemoglobin (g/dL); HCT, hematocrit (%I; MCV, mean corpuscular volume (fL); MCH, mean
corpuscular Hb (pg); MCHC, MCH concentration (g/dL); FS, frameshift.
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2498
CORRESPONDENCE
analogous to the classic murine W allele, which produces no
hematologic phenotype in the heterozygote.11s'2 However, c-kit
mutations apparently account for a very significant fraction of
human piebaldism (we have found pathologic c-kt mutations in
each of the six unrelated probands we have studied) but, as noted
above, anemia has never been described in any of the very large
number of piebald patients reported to date. Furthermore, the one
known patient with homozygous piebaldism exhibited no hematologic abnormalities.
Another possibility may be that most or all mutant c-kit alleles
result in hematologic phenotypes too subtle to be readily detected
on the outbred genetic background of humans. This would be of
considerable interest, as it would suggest that the c-kt-encoded
SCF receptor is not required for normal development and maintenance of the human erythroid cell lineage in vivo. It may be, for
example, that in humans the SCF receptor is functionally redundant in the erythroid lineage.
Alternatively, in humans, in contrast to in mice, most c-kit gene
mutations may result in a relatively severe phenotype that is
incompatible with life, even in the heterozygote, either because of
severe anemia or because of other pleiotropic effects. In this
instance only alleles that have mild effects on erythropoiesis might
be observed. This seems relatively unlikely, as at least some alleles
resulting in intermediate effects might be expected.
Finally, it might also be that in humans some c-kit mutations
result essentially only in pigmentary abnormalities whereas others
result essentially only in hematologic abnormalities, and that these
effects are mutually exclusive. This seems highly improbable, and
runs counter to the aggregate experience with mice carrying
different Walleles, in which c-kit mutations typically exert pleiotropic phenotypic effects.
Whatever the correct explanation, it appears that humans with
piebaldism resulting from c-kit gene mutations do not typically
exhibit the erythropoietic abnormalities often apparent in W
mutant laboratory mice. This difference underscores the need for
caution when predicting the developmental consequences of human genetic disorders based on the analogous animal models.
RICHARD A. SPRITZ
Departments of Medical Genetics and Pediatrics
Laboratoty of Genetics
Universig of Wmconsin
Madison
REFERENCES
1. Martin FH, Suggs SV, Langley KE, Lu HS, Ting J, Okino KH,
Morris CF, McNiece IK, Jacobsen FW, Mendiaz EA, Birkett NC,
Smith KA, Johnson MJ, Parker VP, Flores JC, Pate1 AC, Fisher
EF, Erjavec HO, Herrera CJ, Wypych J, Sachdev RK, Lin C-H,
Cupples RL, Zsebo KM: Primary structure and functional expression of rat and human stem cell factor DNAs. Cell 63:203,1990
2. Zsebo KM, Wypych J, McNiece IK, Lu HS, Smith KA,
Karkare SB, Sachdev RK, Yuschenkoff VN, Birkett NC, Williams
LR, Satyagal VN,Tung W, Bosselman RA, Mendiaz EA, Langley
KE: Identification, purification, and biological characterization of
hematopoietic stem cell factor from Buffalo rat liver-conditioned
medium. Cell 63:195,1990
3. Zsebo KM, Williams DA, Geissler EN, Broudy VC, Martin
FM, Atkins HL, Hsu R-Y, Birkett NC, Okino KH, Murdock DC,
Jacobsen FW,Langley KE, Smith KA, Takeishi T, Cattanach BM,
Galli SJ, Suggs SV: Stem cell factor is encoded at the SI locus of
the mouse and is the ligand for the c-kit tyrosine kinase receptor.
Cell 63:213,1990
4. Anderson DM, Lyman SD, Baird A, Wignall JM, Eisenman J,
Rauch C, March CJ, Boswell HS, Gimpel SD, Cosman D, Williams
DE: Molecular cloning of mast cell growth factor, a hematopietin
that is active in both membrane bound and soluble forms. Cell
63:235,1990
5. Copeland NG, Gilbert DJ, Cho BC, Donovan PJ, Jenkins NA,
Cosman D, Anderson D, Lyman SD, Williams D E Mast cell
growth factor maps near the steel locus of mouse chromosome 10
and is deleted in a number of steel alleles. Cell 63:175,1990
6. Williams DE, Eisenman J, Baird A, Rauch C, Van Ness K,
March CJ, Park LS, Martin U, Mochizuki DY, Boswell HS,
Burgess GS, Cosman D, Lyman SD: Identification of a ligand for
the c-kit proto-oncogene. Cell 63:167,1990
7. Huang E, Nocka K, Beier DR, Chu T-Y, Buck J, Lahm H-W,
Wellner D, Leder P, Besmer P: The hematopoietic growth factor
KL is encoded by the SI locus and is the ligand of the c-kit receptor,
the gene product of the Wlocus. Cell 63:225,1990
8. Flanagan JG, Leder P: The kit ligand: A cell surface molecule
altered in Steel mutant fibroblasts. Cell 63:185,1991
9. Nocka K, Buck J, Levi E, Besmer P: Candidate ligand for the
c-kit transmembrane kinase receptor: KL, a fibroblast derived
growth factor stimulates mast cells and erythroid progenitors.
EMBO J 9:3287,1990
10. Yarden Y, Kuang W, Yang-Feng T, Coussens L, Munemitsu
S, Dull TJ, Chen E, Schlessinger J, Francke U, Ullrich A Human
proto-oncogene c-kit: A new cell surface receptor tyrosine kinase
for an unidentified ligand. EMBO J 6:3341,1987
11. Silvers W K The Coat Colors of Mice. New York, NY,
Springer-Verlag, 1979
12. Lyon MF, Searle AG (eds): Genetic Variants and Strains of
the Laboratory Mouse (ed 2). New York, NY, Oxford University,
1989
13. Giebel LB, Spritz RA.Mutation of the KIT (mast/stem cell
growth factor receptor) protooncogene in human piebaldism. Proc
Natl Acad Sci USA 88:8696,1991
14. Spritz RA, Giebel LB, Holmes SA. Dominant negative and
loss of function mutations of the c-kit (mast/stem cell growth factor
receptor) proto-oncogene in human piebaldism. Am J Hum Genet
50:261,1992
15. Hulttn MA, Honeyman MM, Mayne AJ, Tarlow MJ: Homozygosity in piebald trait. J Med Genet 24568, 1987
16. Andre C, d'Aurio1 L, Lacombe C, Gisselbrecht S, Galibert
F c-kit mRNA expression in human and murine hematopoietic cell
lines. Oncogene 4:1047,1989
17. Migliaccio G, Migliaccio AR, Egrie J, Zsebo K, Adamson
JW: Human stem cell factor (SCF): A hematopoietic growth factor
targeting human multilineage colony-forming cells (CFC) and
capable of generating CFC from pre-CFC. Clin Res 39:190A, 1991
(abstr)
18. Ratajczak M, Luger SM, DeRiel K, Abrahm J, Calabretta B,
YM, Gewirtz A. Role of the c-kit protooncogene in normal and
malignant human hematopoiesis. Proc Natl Acad Sci USA (in
press)
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2499
CORRESPONDENCE
RESPONSE
It is interesting that c-kit mutations in humans cause piebaldism
but no detectable anemia. As Dr Spritz mentions, the humans
characterized thus far are heterozygous for null mutations and, like
the mice with a single copy of the null c-kit, have normal blood
values. Thus, one would not expect the patients to be severely
affected. A cautionary note is that the mice heterozygous for the
null mutant gene are not really normal. Evidence of abnormal
blood formation is the finding that hematopoietic cells from
heterozygotes do not compete well with cells from normal mice
during repopulation.' Thus, piebald patients with no apparent
deleterious effects on hematopoiesis, when stressed by, for example, suppressive anticancer drug treatment, might show severe
abnormalities.
Mice with mutations in c-kit that cause production of a functional but aberrant protein are usually anemic as heterozygotes.
One might expect to find such mutations in the human population.
As Dr Spritz points out, it is surprising that among the many
piebald patients studied to date there is no anemia. However, there
is a major difference between the mice and the humans in that the
mice are highly inbred. Therefore, all the mice are essentially the
same genetically, except at the W locus, whereas the humans are
heterogeneous. How do you evaluate the red blood cell (RBC)
counts between patients and normal sibs when you are looking for
a subtle difference? Even in the mice, it is sometimes difficult to
confirm the anemia in the heterozygote. For example, mice with
the mutation W41Jas heterozygotes have an RBC count of 9.21 2
0.07 (SEM) x 109/mL while the + / + littermates have an RBC
count of 9.84 2 0.04 x 109/mL.ZEven in the affected homozygote,
the RBC count is 8.19 0.09, so there really is not much variation
between normal and mutants. In fact, it required blood tests on
large numbers of mice to prove the difference is statistically
significant.
The information that there is at least one nonanemic homozygous piebald patient from consanguinous parents is not surprising.
There is at least one mouse mutant, Ww/w4,
that is also not
anemic. Again, this mouse has a hematopoietic defect because it
does accept marrow from a normal littermate without prior
irradiation3 and its own marrow cells produce characteristically few
macroscopic spleen colonies in an irradiated +/ host?
Another tissue where there appears to be differences between
human and mouse c-kit mutants is the brain. The mice have no
obvious clinical symptoms of neural insufficiency, despite the fact
that the brain generates more c-kit mRNA than other tissue?
There are, on the other hand, descriptions of piebald patients who
exhibit neurologic problem^.^,^ Given the previous arguments, it is
entirely possible that the mice exhibit subtle differences in brain
physiology that we have not yet discovered (while the piebald
patients actually have aberrant hematopoiesis). If this is the case,
then the piebald patients may, in fact, be excellent models of the
murine disease!
*
+
JANE E. BARKER
The Jackron Laboratory
Bar Harbor ME
REFERENCES
1. Harrison DE: Personal communication, September 1991.
2. Geissler EN, McFarland EC, Russell ES: Analysis of pleiotropism at the dominant spotting (W) locus of the mouse: A
description of ten new alleles. Genetics 97336, 1981
3. Geissler EN, Russell ES: Analysis of the hematopoietic
effects of new dominant spotting (W) mutation of the mouse. I.
Influence upon hematopoietic stam cells. Exp Hematol 11:452,
1983
4. Barker JE, McFarland EC: Hemopoietic precursor cell defects in nonanemic but stem cell-deficient W44/W44mice. J Cell
Physiol135:533, 1988
5. Orr-Urtreger A, Avivi A, Zimmer Y, Givol D, Yarden Y,
Lonai P: Developmental expression of c-kit, a proto-oncogene
encoded by the Wlocus. Develop 109:911,1990
6. Telfer MA, Sugar M, Jaeger AE, Mulcahy J: Dominant
piebald trait (white forelock and leukoderma) with neurological
impairment. Am J Hum Genet 23:383,1971
7. Hoo JJ, Haslam RHA, van Orman C Tentative assignment of
piebald trait gene to chromosome band 4q12. Hum Genet 73:230,
1986
From www.bloodjournal.org by guest on June 17, 2017. For personal use only.
1992 79: 2497-2499
Lack of apparent hematologic abnormalities in human patients with
c-kit (stem cell factor receptor) gene mutations [letter]
RA Spritz
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