The Polyneuropathies Specific Types Inherited Neuropathies

HEREDITARY MOTOR SENSORY NEUROPATHY (HMSN) (Charcot - Marie - Tooth)

A heterogeneous group of disorders with a prevalence of 1:2500 - the largest category of genetic neurological disease. The characteristic appearancc is that of distal wasting. The lower limbs having an 'inverted wine bottle' appearance.

Classification

Clinical

Pathology

Neuro

Inheritance

features

physiology

HMSN

Age of onset < 30 yrs.

Dcmyclination

Motor

Autosomal

type I

Wasting and weakness of

with thickened

conduction

dominant

intrinsic foot muscles,

'onion bulb'

velocities slowed

duplication or

peroneal and tibial groups.

areas of

< 38 m/sec in

point mutation

Distal upper limb

remyelination.

common

chromosome 1

involvement. Pes cavus/

peroneal nerve.

or chromosome

hammer toes - 75%.

17 or X linked -

Palpable peripheral

Point mutation

nerves - 25%.

proximal long

Associated ataxia and

arm of X

tremor - 10%.

chromosome.

HMSN

Age of onset > 30 yrs.

Axonal loss.

Motor

Autosomal

type II

Wasting and weakness as

conduction

dominant -

type I. Foot deformities

velocities normal

mechanism and

absent. Peripheral

or marginally

gene locus

nerves not palpable.

slowed.

unknown.

HMSN type

Age of onset: childhood.

Demyelination

Motor

Autosomal

III (Dejerine

Wasting and weakness may

with 'onion

conduction

recessive - point

- Sottas

be proximal. Peripheral

bulb' formation.

velocities

mutation

disease)

nerves and spinal roots

profoundly

chromosome 1

thickened. CSF

slowed - 5-10

or 17 or sporadic

protein elevated.

m/sec.

Complex forms of HMSN occur. Several pedigrees show additional features such as - optic atrophy, retinopathy, deafness, ataxia, spasticity and cardiomyopathy. Such 'extra' features complicate a simple classification. Treatment is symptomatic with provision of appropriate footwear, splints or orthopaedic procedures to maintain mobility. In adult onset disease, the rate of progression is exceedingly slow. The demonstration of genetic markers and the application of nerve conduction studies allows early and correct diagnosis in those at risk. Nerve biopsy is of no diagnostic value.

Other rare forms of hereditary neuropathy

- Hereditary sensory and autonomic neuropathies - Autosomal recessive

Childhood onset

Characterised by insensitivity to pain and disordered sweating - Autosomal dominant Adult onset

Characterised by recurrent entrapment neuropathies e.g. carpal tunnel syndrome

- Hereditary liability to pressure palsies

- Hereditary neuropathy with spinocerebellar degeneration

- Hereditary neuropathy with metabolic defect e.g. Friedrich's ataxia (pages 532-533) e.g. Familial amyloid neuropathy - mutation of transthyretin gene

Porphyria - abnormality of hepatic haem biosynthesis

Refsums disease - abnormality of phytanic acid metabolism.

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