M

Manifesting carrier

A female carrier of an X-linked condition who exhibits symptoms such as muscle weakness.

Membrane

The barrier between the inside and outside of a cell or between two compartments of a cell. Membranes protect cells and control which substances leave or enter them.

Merosin (laminin alpha 2)

The protein absent in Congenital muscular dystrophy type 1A.

Mitochondria

The ‘energy factories’ of cells. They have their own DNA, inherited from the mother.

Mitochondrial myopathies

Genetic disorders of muscle which affect the mitochondria, caused by either a fault in the DNA of the mitochondria or the nucleus. Without a sufficient supply of energy the cells fail to function properly, causing disease.

Molecule

Two or more atoms (the basic building block of elements) chemically bonded together.

Mouse model

Is a strain or breed of mouse which has a disease that is similar to a human disorder. For example the MDX mouse model of Duchenne muscular dystrophy has a mutation in the dystrophin gene and the muscles of these mice have many features in common with the muscles of boys with Duchenne muscular dystrophy.

Muscle cell

The basic unit of muscle fibre.

Muscle fibre

The basic unit of muscle tissue, formed by the fusion of groups of muscle cells.

Mutation

The alteration of a gene. Mutations can be passed on from generation to generation.

Myasthenia Gravis

A chronic, autoimmune disorder which causes muscle weakness and excessive muscle fatigue, thought to be caused by a faulty immune system.

Myelin

The insulating material that surrounds nerves and allows the quick conduction of nerve impulses.

Myoblast transfer

A potential method of treatment for some forms of muscular dystrophy, which involves transplanting billions of healthy donor cells into dystrophic muscle. Sometimes referred to as cell therapy.

Myopathy

Muscle weakness.

Myositis

Muscle inflammation.

Myotonia

A condition in which muscles are slow to relax after contracting (muscle stiffness).

Myotonic dystrophy

A genetic disorder with symptoms of myotonia, progressive muscle wasting and weakness, usually affecting the face, jaw and neck muscles. Caused by an increased number of repeated units of genetic material (called triplet repeats) within a gene. Exactly how this causes symptoms is not fully understood.

Myotonin protein kinase

In some patients with myotonic dystrophy the increased number of repeated units of genetic material occurs within the gene for the protein – myotonic dystrophy protein kinase.

Myotubularin

The protein absent in individuals with myotubular (centronuclear) myopathy.