Summary
Clinical characteristics.
GATA1-related cytopenia is characterized by thrombocytopenia and/or anemia ranging from mild to severe. One or more of the following may also be present: platelet dysfunction, mild β-thalassemia, neutropenia, and congenital erythropoietic porphyria (CEP) in males. Thrombocytopenia typically presents in infancy as a bleeding disorder with easy bruising and mucosal bleeding (e.g., epistaxis). Anemia ranges from minimal (mild dyserythropoiesis) to severe (hydrops fetalis requiring in utero transfusion). At the extreme end of the clinical spectrum, severe hemorrhage and/or erythrocyte transfusion dependence are life long; at the milder end, anemia and the risk for bleeding may decrease spontaneously with age. Heterozygous females may have mild-to-moderate symptoms such as menorrhagia.
Diagnosis/testing.
Diagnostic laboratory findings usually include macrothrombocytopenia (low number of platelets that are larger than normal) and/or anemia with red cell indices that may be micro-, normo- or macrocytic. Defects in platelet aggregation in response to agonists may be seen. In some cases electron microscopy reveals reduced numbers of platelet alpha granules and dysplastic features in platelets and megakaryocytes.
Management.
Treatment of manifestations: Platelet transfusions for moderate-to-severe epistaxis, gingival bleeding, or gastrointestinal bleeding; no specific treatment for mild symptoms (easy bruisability); erythrocyte transfusions when anemia is symptomatic (fatigue, tachycardia).
Prevention of primary manifestations: For severe cases, bone marrow transplantation (BMT) can be curative.
Surveillance: Monitoring complete blood counts (with frequency depending on disease severity) to inform supportive care; monitoring those undergoing repeated erythrocyte transfusions for iron overload.
Agents/circumstances to avoid: Those with thrombocytopenia should avoid antiplatelet agents including aspirin and nonsteroidal anti-inflammatory agents (e.g., ibuprofen). Those with thrombocytopenia and/or platelet aggregation defects should avoid contact sports or activities with a high risk of trauma.
Evaluation of relatives at risk: If a GATA1 pathogenic variant has been identified in the family, complete blood counts and molecular genetic testing of at-risk relatives can be offered. At-risk relatives who choose not to have molecular genetic testing should have complete blood counts to evaluate for thrombocytopenia, anemia, or neutropenia.
Genetic counseling.
GATA1-related cytopenia is inherited in an X-linked manner. If the mother of an affected male has a GATA1 pathogenic variant, the chance of transmitting it in each pregnancy is 50%. Affected males pass the pathogenic variant to all of their daughters and none of their sons. Testing for at-risk family members and prenatal testing for a pregnancy at increased risk are possible once the pathogenic variant has been identified in the family.
Clinical Characteristics
Clinical Description
Individuals with GATA1-related cytopenia have thrombocytopenia and/or anemia.
Males
Laboratory findings in males
Complete blood count showing the following:
Anemia (hematocrit 16%-35%; normal: 35%-45%) may be present; the severity varies with the specific
pathogenic variant. Red cell indices are normochromic but may be mildly microcytic (75-79 fL) or macrocytic (101-103 fL) (normal: 80-99 fL).
Note: Thrombocytopenia, anemia, and neutropenia are usually defined as two standard deviations below values observed in the normal population.
Peripheral blood smear that may show the following:
Some platelets that are larger and more spherical than the typical discoid morphology. Platelets may be pale, reflecting reduced granularity.
Variation in erythrocyte size and shape and hypochromia, reflecting low hemoglobin content
Bone marrow biopsy that may show the following:
Hyper- or hypocellularity
Increased or decreased numbers of megakaryocytes
Small, dysplastic megakaryocytes with signs of incomplete maturation
Dyserythropoiesis
Hypocellularity of erythroid and granulocytic lineages
Electron microscopy. Findings in some cases include reduced numbers of platelet alpha granules and dysplastic features in megakaryocytes and platelets.
In subtypes associated with globin chain imbalance, findings consistent with mild hemolysis, including mild reticulocytosis, elevated LDH, and low haptoglobin, may be present. In addition, HbA2 and HbF may be elevated.
Terms Used to Describe This Disorder
View in own window
Term | Definition |
---|
Thrombocytopenia
| ↓ platelet count |
Macrothrombocytopenia
| Thrombocytopenia w/large platelets |
Dyserythropoiesis
| Impaired production & maturation of erythrocytes (red blood cells) |
Thalassemia
| An inherited form of anemia assoc w/unbalanced globin chain synthesis |
Hemoglobin
| The oxygen-carrying compound of red blood cells, made up of heme, α-globin, & β-globin. β-thalassemia is assoc w/↓ β-globin synthesis in red blood cells. |
Findings in heterozygous females. Females may manifest platelet abnormalities [White 2007] and mild-to-moderate symptoms such as menorrhagia or easy bruising, presumably related to the proportion of relevant cells that contain the pathogenic GATA1 variant on the active X chromosome [Nichols et al 2000; Raskind et al 2000; Balduini et al 2004; Del Vecchio et al 2005; Raskind, unpublished observations].
Platelet counts may be normal or mildly to moderately decreased [
Nichols et al 2000]; this may depend on the nature of the
pathogenic variant or other (either genetic or environmental) modifiers.
Morphologic abnormalities of platelets can be detected by electron microscopy [
White 2007] and in some instances on peripheral blood smears [
Tubman et al 2007].
Course and prognosis. The long-term course in both males and females depends on disease severity:
At the extreme end of the clinical spectrum, severe hemorrhage and/or erythrocyte transfusion dependence are life long.
Some affected individuals may be recognized only after incidental findings of mild-to-moderate cytopenias on blood count analysis. These individuals have a good prognosis.
Genotype-Phenotype Correlations
outlines the relationship between specific GATA1 pathogenic variants and associated phenotypic features.
Table 2.
Genotype-Phenotype Correlations
View in own window
Pathogenic Variant 1 | Platelet Phenotype 2 | Platelet Aggregation | Red Cell Phenotype | Other Features | References |
---|
| ↓ Large | Not studied | ↓ Dyserythropoietic, fetal hydrops | Cryptorchidism 3 |
Nichols et al [2000]
|
| ↓ Large | Decreased | Normal | | Mehaffey et al [2001] 4, 5 |
| ↓↓ Large | Not studied | ↓ Dyserythropoietic | Cryptorchidism in proband but also in 2 sibs w/wild type GATA1 3 | Del Vecchio et al [2005], Kratz et al [2008] 4, 5 |
| ↓ Large | Normal, but prolonged bleeding time | Mild β-thalassemia, mild anemia | Splenomegaly | Thompson et al [1977], Raskind et al [2000], Yu et al [2002], Balduini et al [2004], Hughan et al [2005], Tubman et al [2007], Campbell et al [2013], Ǻström et al [2015] |
| ↓ | Not reported | Mild β-thalassemia | Congenital erythropoietic porphyria, splenomegaly | Hindmarsh [1986], Phillips et al [2007], Ged et al [2009], Campbell et al [2013] |
| ↓ Large | Decreased | Dyserythropoiesis without anemia | | Freson et al [2001], White [2007], White et al [2007] |
| ↓↓ Large | Not studied | Severe anemia | Platelets in carrier female expressed only wild type allele |
Freson et al [2002]
|
| ↓ Large | Not studied | Normal | Lu(a-b-) red cells |
Singleton et al [2013]
|
| Normal counts, but dysplastic megakaryocytes | Decreased | Macrocytic anemia of variable severity | Neutropenia |
Hollanda et al [2006]
|
| Normal or ↓ | Not studied | Macrocytic anemia of variable severity | |
Sankaran et al [2012]
|
| Normal | Not studied | Anemia | |
Sankaran et al [2012]
|
| Normal | Not studied | Macrocytic anemia | |
Klar et al [2014]
|
| ↓ | Not studied | Anemia | |
Parrella et al [2014]
|
- 1.
- 2.
Decreased platelet alpha granules are observed in all affected males studied.
- 3.
Cryptorchidism has been reported in several males with GATA1 pathogenic variants [Nichols et al 2000, Del Vecchio et al 2005]. Although Gata1 is expressed in mouse testis, knockout of Gata1 in Sertoli cells within the testis had no effect, suggesting that Gata1 is not essential for Sertoli cell function [Lindeboom et al 2003]. The independent segregation of cryptorchidism and GATA1 pathogenic variants in one of the two families [Del Vecchio et al 2005], in conjunction with the mouse data, make the mechanistic relationship between GATA1 pathogenic variants and cryptorchidism unclear at this point.
- 4.
No response to splenectomy and/or steroids
- 5.
Decreased bleeding episodes with age, despite persistence of thrombocytopenia
For further information on murine and in vitro experiments involving GATA-1, see Molecular Genetics, Pathogenic variants.
Nomenclature
Until pathogenic variants in GATA1 were shown to underlie this heterogeneous disorder, a variety of terms were coined for the different clinical presentations. The first term used was X-linked thrombocytopenia with thalassemia (XLTT) [Raskind et al 2000]. Other terms used in the past and still in the current literature are "familial dyserythropoietic anemia and thrombocytopenia" [Nichols et al 2000, Del Vecchio et al 2005] and "X-linked macrothrombocytopenia" [Freson et al 2001].
To describe individuals with a clinical diagnosis of Diamond-Blackfan anemia in whom GATA1 pathogenic variants are identified and ribosomal protein variants are absent, the authors suggest the phrase "variant DBA associated with pathogenic variant of GATA1."
Prevalence
GATA1-related cytopenia is rare; the prevalence is not known. To date, hematopoietic disease caused by inherited pathogenic variants in GATA1 has been reported in 22 families [Nichols et al 2000, Freson et al 2001, Mehaffey et al 2001, Freson et al 2002, Yu et al 2002, Balduini et al 2004, Del Vecchio et al 2005, Hughan et al 2005, Phillips et al 2005, Hollanda et al 2006, Sankaran et al 2012, Singleton et al 2013, Hermans et al 2014, Klar et al 2014, Parrella et al 2014, Åström et al 2015, Di Pierro et al 2015, Zucker et al 2016].
GATA1 pathogenic variants may be more common than previously appreciated, particularly in persons with mild, unexplained thrombocytopenia/"gray platelet syndrome" present since birth [Tubman et al 2007] or individuals with congenital hypoplastic anemia/Diamond-Blackfan anemia with no ribosomal protein pathogenic variants [Sankaran et al 2012].
Differential Diagnosis
GATA1-related cytopenia must be distinguished from other acquired and inherited thrombocytopenias and platelet function abnormalities [Balduini & Savoia 2004, Drachman 2004] (see ). Algorithms exist to help differentiate among these disorders [Drachman 2004, Noris et al 2004].
Because of its X-linked mode of inheritance and association with thrombocytopenia, Wiskott-Aldrich syndrome (WAS) can be confused with GATA1-related cytopenia. Distinguishing features of WAS include small platelets, eczema (~80%), and immunodeficiency, although individuals with milder pathogenic variants may manifest with microthrombocytopenia only.
In GATA1-related cytopenia, platelets are usually large and may be hypogranular. Relatively common congenital causes of macrothrombocytopenia that could potentially be confused with GATA1-related disorders are described in .
Table 3.
Etiology and Characteristics of Other Inherited Syndromes of Macrothrombocytopenia
View in own window
Name | Gene | Mode of Inheritance | Features |
---|
Bernard-Soulier syndrome (OMIM 231200) |
GP1BA
GP1BB
GP9
| AR 1 |
|
MYH9-related syndromes
|
MYH9
| AD |
|
Mediterranean thrombocytopenia (OMIM 153670) |
GP1BA
| AD |
|
Paris-Trousseau thrombocytopenia (OMIM 188025) | See footnote 2. | AD |
|
Jacobsen syndrome (OMIM 147791) |
22q11.2 deletion syndrome
| See footnote 3. | AD |
|
Gray platelet syndrome (OMIM 139090) | NBEAL2 GATA1 4 | See footnote 5. | Pale platelets ↓ or absent α-granules
|
- 1.
Heterozygotes may have mild disease.
- 2.
- 3.
- 4.
- 5.
Management
Evaluations Following Initial Diagnosis
To establish the extent of disease and needs in an individual diagnosed with GATA1-related cytopenia, the following are recommended:
Complete blood count and examination of the peripheral smear to assess the degree of cytopenia(s)
Detailed history of age at which hematologic disease was manifest
Documentation of abnormal/unexpected bleeding episodes and platelet counts obtained at the time of the episodes to help determine whether platelet function is abnormal and whether disease severity has changed over time
Note: Platelet aggregation studies may also be useful to identify functional abnormalities that predict a greater risk of bleeding for any given platelet count, but studies can be difficult to interpret when platelet counts are lower than 100,000/μL.
Consultation with a clinical geneticist and/or genetic counselor
Treatment of Manifestations
Individuals with GATA1-related cytopenia are treated supportively.
Thrombocytopenia. Individuals with moderate-to-severe epistaxis, gingival bleeding, or gastrointestinal bleeding should receive platelet transfusions. Transfusion requirements vary from person to person as bleeding can be related to quantitative and/or qualitative platelet defects.
For individuals with thrombocytopenia and/or platelet aggregation defects, DDAVP treatment may be helpful for short-term management of mild-to-moderate bleeding.
Individuals who are only mildly symptomatic (easy bruisability without mucosal or more severe bleeding) do not require specific treatment.
There is no evidence that splenectomy is beneficial in people with GATA1-related disease, although this treatment may be considered if splenomegaly is severe. Although splenectomy may improve the cytopenias, platelet dysfunction will not be improved.
Anemia. Erythrocyte transfusions are indicated when anemia is symptomatic (fatigue, tachycardia).
Iron overload and the development of alloantibodies may limit chronic transfusion therapy.
Extended pre-transfusion red blood cell phenotyping and matching for minor erythrocyte antigens in individuals receiving frequent transfusions can reduce the risk of alloimmunization.
Neutropenia. Individuals with neutropenia who present with fever should be evaluated promptly with a physical examination, complete blood count, and blood culture and should receive appropriate parenteral antibiotics.
Bone marrow transplantation (BMT). For severe cases, BMT can be curative [Hollanda et al 2006, Phillips et al 2007, Parrella et al 2014].
BMT should be considered in individuals with severe phenotypes of GATA1-related cytopenia, particularly if an HLA-matched donor is available.
While BMT may offer a cure, clinical experience with BMT in this disease is limited and families must be counseled on the significant risks and morbidity associated with BMT.
Prevention of Primary Manifestations
The only definitive cure for GATA1-related cytopenia is bone marrow transplantation.
Prevention of Secondary Complications
Individuals with thrombocytopenia and/or platelet aggregation defects should receive a platelet transfusion prior to surgical or invasive dental procedures.
Individuals with neutropenia should be counseled regarding their increased risk of infection. They should avoid crowds and contact with individuals who have communicable diseases. When febrile, those who are severely neutropenic (absolute neutrophil count <500/µL) should seek medical attention; typically blood cultures are obtained and parenteral antibiotics are administered to avoid the possibility of life-threatening sepsis.
Surveillance
Depending on the phenotype of the disease, complete blood counts should be monitored so that supportive care can be provided as needed. Individuals with mild cytopenias require infrequent monitoring (yearly), while those with severe cytopenias who require transfusions should have complete blood counts monthly or as indicated by clinical signs and symptoms.
Individuals undergoing repeated erythrocyte transfusions should be monitored for iron overload and managed appropriately with iron chelation therapy.
Agents/Circumstances to Avoid
Individuals with thrombocytopenia should avoid antiplatelet agents including aspirin and nonsteroidal anti-inflammatory agents (e.g., ibuprofen).
Individuals with thrombocytopenia and/or platelet aggregation defects should be advised to avoid contact sports or activities with a high risk of trauma.
Individuals with significant neutropenia should avoid crowds and close contact with persons who have a communicable disease to minimize risk of infection.
Individuals with significant splenomegaly should avoid contact sports, which involve increased risk for traumatic splenic rupture.
Evaluation of Relatives at Risk
It is appropriate to evaluate apparently asymptomatic at-risk relatives of an affected individual in order to identify as early as possible those who would benefit from prompt initiation of treatment and preventive measures.
Evaluations can include:
See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.
Therapies Under Investigation
Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.
Other
Unlike immune-mediated platelet disorders such as immune thrombocytopenic purpura, GATA1-related thrombocytopenia does not respond to steroid or immunoglobulin therapy.
Supplemental erythropoietin therapy is unlikely to be effective because the anemia is secondary to ineffective erythropoiesis, not erythropoietin deficiency.
Genetic Counseling
Genetic counseling is the process of providing individuals and families with
information on the nature, mode(s) of inheritance, and implications of genetic disorders to help them
make informed medical and personal decisions. The following section deals with genetic
risk assessment and the use of family history and genetic testing to clarify genetic
status for family members; it is not meant to address all personal, cultural, or
ethical issues that may arise or to substitute for consultation with a genetics
professional. —ED.
Mode of Inheritance
GATA1-related cytopenia is inherited in an X-linked manner.
Risk to Family Members
Parents of a male proband
The father of an affected male will not have the disorder nor will he be
hemizygous for the
GATA1 pathogenic variant; therefore, he does not require further evaluation/testing.
In a family with more than one affected individual, the mother of an affected male is an
obligate heterozygote (
carrier). If a woman has more than one affected son and no other affected relatives and if the
pathogenic variant cannot be detected in her leukocyte DNA, she has
germline mosaicism (evidence of germline mosaicism has not been observed).
If a male is the only affected family member (i.e., a
simplex case), the mother may be a
heterozygote (
carrier) or the affected male may have a
de novo
GATA1 pathogenic variant, in which case the mother is not a carrier. Because very few families with
GATA1 pathogenic variants have been described to date, the frequency of
de novo pathogenic variants is not known.
Sibs of a male proband. The risk to sibs depends on the genetic status of the mother:
Females who inherit the
pathogenic variant will be
heterozygous and will usually not be affected, but may have reduced hematocrits and platelet counts to a variable degree. Large platelets may also be present and those with the globin chain imbalance subtype may have splenomegaly and slightly decreased β-globin synthesis.
If the
proband represents a
simplex case (i.e., a single occurrence in a family) and if the
GATA1 pathogenic variant cannot be detected in the leukocyte DNA of the mother, the risk to sibs is slightly greater than that of the general population (though still <1%) because of the theoretic possibility of maternal
germline mosaicism.
Offspring of a proband. Affected males transmit the GATA1 pathogenic variant to:
All of their daughters, who will be carriers (heterozygotes) and will usually not be affected (see
Clinical Description);
None of their sons.
Other family members. The proband's maternal aunts may be at risk of being heterozygotes (carriers) for the pathogenic variant and the aunts' offspring, depending on their sex, may be at risk of being heterozygotes (carriers) for the pathogenic variant or of being affected.
Heterozygote Detection
Molecular genetic testing of at-risk female relatives to determine their genetic status is most informative if the pathogenic variant has been identified in the proband.
Note: Females who are heterozygotes (carriers) for this X-linked disorder may develop clinical findings related to the disorder (see Clinical Description).
Molecular Genetics
Information in the Molecular Genetics and OMIM tables may differ from that elsewhere in the GeneReview: tables may contain more recent information. —ED.
Table A.
GATA1-Related X-Linked Cytopenia: Genes and Databases
View in own window
Data are compiled from the following standard references: gene from
HGNC;
chromosome locus from
OMIM;
protein from UniProt.
For a description of databases (Locus Specific, HGMD, ClinVar) to which links are provided, click
here.
Table B.
View in own window
300367 | THROMBOCYTOPENIA, X-LINKED, WITH OR WITHOUT DYSERYTHROPOIETIC ANEMIA; XLTDA |
305371 | GATA-BINDING PROTEIN 1; GATA1 |
314050 | THROMBOCYTOPENIA WITH BETA-THALASSEMIA, X-LINKED; XLTT |
Gene structure.
GATA1 has six exons, although the first exon is non-coding and is not counted in some of the literature. For a detailed summary of gene and protein information, see Table A, Gene.
Pathogenic variants. Most germline GATA1 variants associated with cytopenias are missense variants. These variants cluster in exon 4 amino acid residues 205, 208, 216, and 218 within the amino-terminal zinc finger domain. They either affect erythroid transcription factor (GATA-1) binding to DNA or interaction of GATA-1 with its essential cofactor, friend of GATA (FOG)-1 [Nichols et al 2000, Freson et al 2001, Mehaffey et al 2001, Freson et al 2002, Yu et al 2002, Balduini et al 2004, Del Vecchio et al 2005].
A pathogenic variant in exon 2 of GATA1 that alters splicing was found in one family with anemia and neutropenia [Hollanda et al 2006]. Similar variants have been identified in several families with Diamond-Blackfan anemia without pathogenic ribosomal protein variants [Sankaran et al 2012, Parrella et al 2014, Klar et al 2014, Zucker et al 2016] and unpublished studies by several groups. These variants result in the exclusive production of an amino-truncated isoform of GATA-1, termed GATA-1s (for GATA-1 short; also discussed in Genetically Related Disorders). In the context of Down syndrome (DS, trisomy 21), somatic variants resulting in the production of only GATA-1s are associated with leukemia and transient myeloproliferative disorder (TMD) [Wechsler et al 2002]; however, the same GATA1 variants present in the germline of persons who do not have DS cause cytopenia but not leukemia [Hollanda et al 2006]. In mice, analogous variants increase the proliferative capacity of embryonic megakaryocyte precursors but produce a minimal hematopoietic phenotype in adults [Li et al 2005].
Cis element variants affecting GATA-1 binding to target genes have also been implicated in red cell production or function. For example, Africans frequently carry a variant in the Duffy antigen/chemokine receptor (DARC) gene promoter that disrupts GATA-1 binding [Tournamille et al 1995]. This leads to the common African Duffy negative red cell phenotype, which confers resistance to Plasmodium vivax malaria.
Congenital erythropoietic porphyria (CEP) can also be caused by variants in the promoter region of the gene encoding the heme synthetic enzyme uroporphyrinogen III synthase, where GATA-1 normally binds [Solis et al 2001].
X-linked sideroblastic anemia (XLSA) typically results from partial loss-of-function missense variants in the erythroid-specific heme biosynthesis protein 5-aminolevulinate synthase 2 (ALAS2). Variants in the GATA binding site located in a transcriptional enhancer element in ALAS2 have been identified in several pedigrees with XLSA [Campagna et al 2014, Kaneko et al 2014].
As a master regulator of erythrocyte and megakaryocyte/platelet development, GATA1 both activates and represses hundreds of genes in each of these lineages. Presumably, different missense variants in GATA1 cause distinct phenotypes by altering the expression of specific subsets of target genes. These pathogenic variants could affect GATA1 DNA binding, interactions with cofactors, or both. Both of these properties of the GATA zinc fingers have been mapped by structural studies. However, recent analysis of GATA1 pathogenic variants in murine complementation systems showed that structural studies and in vitro examination of purified recombinant proteins did not always accurately elucidate the effects of variants, and in vivo studies are required [Campbell et al 2013]. Specifically, p.Arg216Gln and p.Arg216Trp variants that impaired DNA binding in vitro did not measurably affect in vivo target gene occupancy. Instead, diminished TAL1 complex recruitment to GATA-1 target genes was implicated. Thus, establishing genotype-phenotype relationships in GATA1-associated anemias and thrombocytopenias presents a complex but worthwhile challenge that will likely elucidate general concepts of transcription factor function and human disease.
Table 4.
GATA1 Pathogenic Variants Discussed in This GeneReview
View in own window
DNA Nucleotide Change (Alias 1) | Predicted Protein Change | Reference Sequences |
---|
c.2T>C | p.Met1_Cys83del 2 |
NM_002049.3
NP_002040.1
|
c.220G>C 3 | p.Val74Leu |
c.220+1delG 4 | |
c.613G>A | p.Val205Met |
c.622_623delGGinsTC (622_623GG>TC) | p.Gly208Ser |
c.622G>C | p.Gly208Arg |
c.647G>A | p.Arg216Gln 5 |
c.646C>T | p.Arg216Trp |
(332G>C) 6 | |
c.652G>T | p.Asp218Tyr |
c.653A>G | p.Asp218Gly |
c.1240T>C | p.Ter414ArgextTer42 7 |
Variants listed in the table have been provided by the authors. GeneReviews staff have not independently verified the classification of variants.
GeneReviews follows the standard naming conventions of the Human Genome Variation Society (varnomen.hgvs.org). See Quick Reference for an explanation of nomenclature.
- 1.
Variant designation that does not conform to current naming conventions
- 2.
Obliterates initiation codon; alternative initiation Met84 residue is used, resulting in lack of full length cDNA [Parrella et al 2014].
- 3.
- 4.
- 5.
- 6.
- 7.
Pathogenic variant in stop codon 414 results in addition of 41 amino acids and use of new stop codon at residue 42 [Singleton et al 2013].
Normal gene product.
GATA1 encodes a nuclear protein of 413 amino acid residues that contains two zinc fingers and an acidic amino terminal domain that can function as a transcriptional activator [Ferreira et al 2005, Lowry & Mackay 2006]. The C-terminal zinc finger is responsible for DNA binding activity for most or all target genes and the N-terminal zinc finger plays a role in stabilization of GATA-1 binding to DNA at a subset of target sites containing duplicated or palindromic GATA-1 motifs [Ohneda & Yamamoto 2002]. The N-f is also critical for binding of GATA-1 to numerous partner proteins, including FOG1, an essential factor required for many GATA-1 functions [Tsang et al 1997, Fox et al 1999]. GATA-1 is expressed in hematopoietic lineages and in Sertoli cells of testis. Gene targeting studies in mice indicate that GATA-1 is essential for the development of erythrocyte, megakaryocyte, mast cell, and eosinophil lineages. It is not known whether individuals with inherited GATA1 pathogenic variants have defects in the latter two cell lineages.
Abnormal gene product. All pathogenic variants are missense variants, indels, nonsense variants, or splice site substitutions resulting in the production of an abnormal protein. Missense variants in N-f affect its ability to bind either GATA1 sites in DNA, the cofactor FOG1, or both. Splice site variants result in a short form of the protein, GATA-1s. Mice genetically engineered to express GATA-1s show prenatal anemia and megakaryocyte proliferation, but newborn and adult mice display no hematopoietic abnormalities [Li et al 2005]. The functions of these abnormal proteins and their relationship to disease phenotypes are discussed in Genotype-Phenotype Correlations and in .
Cancer and Benign Tumors
Two hematopoietic disorders in children with Down syndrome (DS) associated with acquired (somatic) pathogenic variants in exon 2 of GATA1 are transient myeloproliferative disorder (TMD) and acute megakaryoblastic leukemia (M7 subtype, DS-AMKL) [Wechsler et al 2002, Elagib et al 2003, Waltzer et al 2003, Ahmed et al 2004, Creutzig et al 2005, Crispino 2005a, Crispino 2005b, Muntean et al 2006, Roy et al 2009, Roberts et al 2013].
TMD, found in up to 10% of infants with DS, usually resolves spontaneously; however, TMD confers a markedly increased risk for DS-AMKL [Wechsler et al 2002, Ahmed et al 2004, Crispino 2005a, Crispino 2005b, Hitzler & Zipursky 2005]. The acquired exon 2 variants lead to premature arrest of translation and reinitiation of protein synthesis at the downstream methionine codon at position 83, and result in the production of GATA-1 short isoform (GATA-1s) that lacks the amino-terminal activation domain. Some splice site variants also result in generation of GATA-1s. Two novel GATA1 variants involving internal deletions of either amino acids 77-199 or 74-88 were identified in six individuals with TMD [Toki et al 2013]. How GATA1 variants synergize with trisomy 21 to promote DS-AMKL is unknown.
One individual with severe anemia and thrombocytopenia caused by a pathogenic missense variant in GATA1 (p.Val205Met) developed myelodysplastic syndrome 18 years after a failed bone marrow transplantation. It is not clear whether the MDS with a clonal deletion of 20q was due to the underlying disease caused by the pathogenic variant of GATA1, bone marrow transplant associated toxicity, or both [Authors, unpublished data].