Definition

The MPL gene encodes the thrombopoietin receptor; the W515L, W515K and S505N mutations in exon 10 are gain-of-function mutations that activate the receptor independent of its ligand. W515L/K mutations are found in 1-10% of JAK2 V617F-negative essential thrombocythemia and primary myelofibrosis cases; S505N has been reported in both familial and, rarely, sporadic cases.

Gene/region examined

MPL Exon 10

Method

DNA analysis

Accepted sample types

Blood (EDTA), Bone marrow (EDTA)

Description

Essential Thrombocythemia (ET), Myeloid Metaplasia with Myelofibrosis.

Inheritance

Both are possible for this group, W515L/W515K are somatic mutations; S505N has been described in both germline (hereditary, a founder mutation in familial thrombocythemia pedigrees) and somatic (sporadic) forms, and this distinction should be evaluated separately in clinical interpretation.

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Inheritance Patterns

Describes how a genetic condition is passed on within a family. There are five main patterns

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Carrier (Heterozygous / Homozygous)

Why it matters: In autosomal recessive inheritance, when each parent is a carrier (while both appear healthy), the chance of their child being born with the disease is 25% in each

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VUS (Variant of Uncertain Significance)

This is the situation where the test has detected a change in the DNA, but the role of this change in the development of disease is unconfirmed.

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How to Read a Genetic Test Result (Positive / Negative / VUS)

A genetic test result falls into three main categories

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Types of Genetic Tests

A genetic test is a type of medical test that detects changes in genes, chromosomes or proteins. Today there are more than 77,000 genetic tests available.

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