Definition

Biallelic pathogenic variants in the MMAA, MMAB, or MMACHC genes disrupt the adenosylcobalamin synthesis step of cobalamin (B12) metabolism; this cofactor deficiency impairs the function of methylmalonyl-CoA mutase. MMAA variants cause the cblA type, and MMAB variants cause the cblB type; the cblA type, and to a lesser extent the cblB type, respond well to pharmacologic-dose hydroxocobalamin therapy.

Gene/region analyzed

MMAB - Whole Gene

Method

Sequence analysis

Accepted sample types

EDTA blood, AF, CVS

Inheritance

Hereditary, autosomal recessive.

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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