Definition

The PMP22 gene encodes peripheral myelin protein 22, produced by Schwann cells in peripheral nerves, which plays a role in the structural integrity of the myelin sheath. The most common cause of CMT1A is not a point mutation but duplication of the region on chromosome 17, meaning the presence of an extra copy of the gene; this accounts for approximately 70 to 80% of all CMT1 cases. For this reason, the first step in diagnosis is MLPA/deletion-duplication analysis, which detects this duplication that standard sequence analysis cannot capture.

Gene/region examined

PMP22 - .Exon 2, PMP22 - Exon 3, PMP22 - .Exon 4, PMP22 - .Exon 5

Method

Sequence analysis

Accepted sample types

EDTA blood, AF, CVS

Inheritance

Autosomal dominant, approximately 70 to 80% of cases are inherited from an affected parent, the remainder are new (de novo) duplications.

Related Tests

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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