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Disease Profile

Congenital amegakaryocytic thrombocytopenia

Prevalence
Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.

Unknown

Age of onset

Neonatal

ICD-10

D61.0

Inheritance

Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease

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Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype

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X-linked
dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.

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X-linked
recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder

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Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.

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Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.

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Not applicable

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Other names (AKA)

Thrombocytopenia congenital amegakaryocytic; CAMT

Categories

Blood Diseases; Congenital and Genetic Diseases

Summary

The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.
orphanet

Orpha Number: 3319

Definition
An isolated constitutional thrombocytopenia characterized by an isolated and severe decrease in the number of platelets and megakaryocytes during the first years of life that develops into bone marrow failure with pancytopenia later in childhood.

Epidemiology
Congenital amegakaryocytic thrombocytopenia (CAMT) prevalence is unknown and less than 100 cases have been reported in the literature. In addition, the incidence may be underestimated due to difficult and inconsistent diagnosis of the disease.

Clinical description
CAMT manifests since birth, often in the first day or at least within the first month of life, with petechiae, purpura, and gastrointestinal, pulmonary or intracranial hemorrhage due to isolated thrombocytopenia and a near absence of megakaryocytes in the bone marrow. Two types of CAMT have been identified. Type I-CAMT is the severe form of the disease and is characterized by persistently low platelet counts and early progression (usually by the age of 2 years) to bone marrow aplasia associated with pancytopenia. Type II-CAMT is a milder form which presents with transient increase of platelet counts over 50x109/L during the first year of life and late (by the age of 3-6 years) or no development of pancytopenia. Cardiac defects (atrial and ventricular septal defects), abnormalities of the central nervous system (cerebral and cerebellar hypoplasia), and retardation of psychomotor development have occasionally been reported.

Etiology
CAMT is due to mutations in the MPL gene (1p34) coding for Thrombopoietin (TPO) receptor (c-MPL), expressed in pluripotent hematopoietic stem cells and cells of the megakaryocyte lineage. The binding of TPO to c-MPL stimulates platelet and megakaryocyte production. Different types of mutations have been associated with different phenotypes. Nonsense mutations predicted to result in a complete loss of function of the TPO receptor lead to type I-CAMT, whereas missense mutations predicted to lead to a residual function of the receptor are associated with type II-CAMT. Cases with no defects in the MPL gene are referred to as type III-CAMT. Recently, a 21q22 deletion resulting in RUNX1 haploinsufficiency has been reported in a case of CAMT associated with various anomalies (growth retardation, hearing deficits, hernias, poor feeding).

Diagnostic methods
Diagnosis is based on clinical signs, on the evidence by blood tests of thrombocytopenia (platelet count below 50x109/L) with a normal mean platelet volume and of highly elevated serum levels of TPO, and on the observation in a bone marrow aspirate of absent or very few megakaryocytes. Genetic testing can confirm the diagnosis.

Differential diagnosis
The initial presentation of CAMT with isolated thrombocytopenia can be misdiagnosed as idiopathic thrombocytopenic purpura (ITP), while the late pancytopenic phase is indistinguishable from aplastic anemia. Fanconi anemia, thrombocytopenia-absent radius (TAR), syndrome and Wiscott-Aldrich syndrome (WAS) should be also ruled out.

Antenatal diagnosis
Prenatal diagnosis is possible for families in which the disease-causing mutation has been identified.

Genetic counseling
The inheritance pattern is autosomal recessive. Genetic counseling should be proposed to individuals having the disease-causing mutation informing them that there is 25% risk of passing the mutation to offspring.

Management and treatment
Management is supportive, mainly consisting of multiple platelet transfusions. At present, hematopoietic stem cell transplantation (HSCT) is the only curative therapy.

Prognosis
Prognosis is poor and with supportive therapy, progression to full marrow failure (tri-linear marrow aplasia) occurs during the first years of life. 30% of patients with CAMT die due to bleeding complications before the HSCT and 20% due to the HSCT.

Visit the Orphanet disease page for more resources.

Symptoms

This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
HPO ID
80%-99% of people have these symptoms
Abnormal hemoglobin
0011902
Thrombocytopenia
Low platelet count
0001873
30%-79% of people have these symptoms
Abnormal form of the vertebral bodies
0003312
Anemia
Low number of red blood cells or hemoglobin
0001903
Coarse facial features
Coarse facial appearance
0000280
Melanocytic nevus
Beauty mark
0000995
Scoliosis
0002650
Short neck
Decreased length of neck
0000470
Short stature
Decreased body height
Small stature

[ more ]

0004322
5%-29% of people have these symptoms
Abnormal cardiac septum morphology
0001671
Decreased skull ossification
Decreased bone formation of skull
0004331
Percent of people who have these symptoms is not available through HPO
Amegakaryocytic thrombocytopenia
0004859
Autosomal recessive inheritance
0000007
Cerebellar vermis hypoplasia
0001320
Megakaryocytopenia
0005548
Pancytopenia
Low blood cell count
0001876

Diagnosis

Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.

    Organizations

    Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

    Organizations Supporting this Disease

      Learn more

      These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

      Where to Start

      • The National Cancer Institute provides the most current information on cancer for patients, health professionals, and the general public.

        In-Depth Information

        • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
        • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
        • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
        • PubMed is a searchable database of medical literature and lists journal articles that discuss Congenital amegakaryocytic thrombocytopenia. Click on the link to view a sample search on this topic.