Rare diseases · Sign or symptom

Increased micromegakaryocyte count

HP:0031386

What it means

The presence of abnormally high numbers of micromegakaryocytes in the bone marrow. Micromegakaryocytes are mononuclear diploid cells, with a nucleus similar in size to that of a myeloblast or promyelocyte with the cell being less than 30 micrometers in diameter.

Micromegakaryocytes are characteristic of myelodysplastic syndromebut may be seen in other conditions.

Rare diseases that can present with this1

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category

Increased micromegakaryocyte count

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This page uses the Human Phenotype Ontology (2026-06-23) — Human Phenotype Ontology Consortium, hpo.jax.org. Disease associations from Orphanet (INSERM), CC BY 4.0. Content is educational and is not medical advice.