ARCH	Age-related clonal hematopoiesis is an accelerated version of CHIP, occurring after the age of 60 years.
ACVR1	Activin A Receptor Type 1, also known as ALK-2, is a member of the BMP/TGF-β receptor family.
CHIP	Clonal hematopoiesis with an indeterminate potential is a syndrome characterized by the acquisition of gene mutations by hematopoietic stem cells (HSCs) as they age, with a MAB of ≥2%. Most of these mutations are not potentially deleterious, but a few are, including DNM3Ta, ASXL1, TP53, TET2, and JAK2 V617F.
Contiguous gene syndrome	Contiguous gene syndrome (CGS) is a de novo or treatment-related genetic disorder in which chromosomal copy number changes involving multiple neighboring genes occur, causing del(5q) or –7/del(7q) or complex karyotypes with an adverse prognosis.
Erythremia	An archaic term for polycythemia vera.
Genotype	The genetic basis for phenotype.
Homologous recombination	A mechanism for exchanging genes between similar DNA molecules.
Latency	The time between a biologic change, such as the acquisition of a gene mutation, and the phenotypic expression of that mutation.
LOH	Loss of heterozygosity occurs when a single allele or a larger segment of DNA is lost from a normal chromosome by one of several mechanisms, including gene mutation, deletion, or mitotic recombination, and most commonly in MPNs by uniparental disomy (UPD).
MAB	Mutation allele burden, also known as the VAF, or variant allele fraction, is the percentage of chromosomes in a cell that carries a particular gene mutation. Either one allele (heterozygosity for the mutation) or both alleles of the gene (homozygosity for the mutation) can be involved.
Newtonian fluid	A fluid whose shear stress from flow is linearly correlated with its rate of change in deformation over time.
Next-generation sequencing	Massive, parallel DNA sequencing, also known as NGS, allows the interrogation of the human genome accurately and rapidly to detect gene mutations.
Nitric oxide scavenging	When nitric oxide in the blood stream is bound by either free hemoglobin or red cells, vasoconstriction and increased platelet adherence to the vascular endothelium occur.
Non-Newtonian fluid	The behavior of a fluid that deviates from Newton’s law of viscosity. As an example, blood is more viscous when flowing slowly than when it is flowing rapidly.
Pagophagia	A form of Pica in which disordered gustatory behavior focuses on eating ice.
Phenotype	The observable features of an individual.
Penetration	The extent to which a genetic change is expressed.
Phenotypic mimicry	When appearance is clinically deceiving, which is a particular problem with MPNs, where the same mutation causes two or three different disease phenotypes.
Reactive oxygen species	Reactive oxygen species, such as superoxide, singlet oxygen, hydroperoxide, or hydroxyl radicals, are unstable and can damage DNA, RNA, or proteins.
Ribonucleotide reductase	This enzyme catalyzes the reduction in ribonucleotides to deoxyribonucleotides for use in DNA synthesis. It is a target for hydroxyurea, which destroys its tyrosyl free radical.
JAK2 pseudokinase domain	This is a region of the JAK2 protein that lacks the necessary residues to be a kinase, but can act as an inhibitor of the protein’s tyrosine kinase domain.
Uniparental disomy	Acquired uniparental disomy (UPD), a common feature of PV, is a mitotic recombination resulting in an exchange of genes inherited from one parent on the same segment of one of two homologous chromosomes, causing the copy neutral loss of heterozygosity that is undetectable by cytogenetics.