Hereditary motor and sensory neuropathies in Swedish children. II. Neuronal-axonal types

Lethal neonatal autosomal recessive axonal sensorimotor polyneuropathy

Peripheral neuropathy is an uncommon cause of generalized hypotonia and weakness in infancy. It occurs as a part of the clinical syndrome in some neurodegenerative disorders of infancy, but seldom causes respiratory failure or swallowing difficulties. We report a lethal autosomal recessive axonal polyneuropathy with neonatal onset in a large kindred from Northern Mississippi. One patient was studied in detail at our medical center and the information on 12 other affected infants in this large family were gathered from medical records and by interviewing the family members. Patients were symptomatic for the polyneuropathy before birth and died in the first year of life from respiratory complications. Thirteen babies were affected by this clinical phenotype in four generations of this family with a high frequency of consanguinity. Affected babies were of both sexes and were born to healthy consanguineous parents. The clinical phenotype of polyneuropathy in our index patient and other affected babies in this family was similar, and represents a unique form of hereditary neonatal polyneuropathy.

Hereditary motor and sensory neuropathy: HMSN type II (neuronal type) and X-linked HMSN

The neuronal forms of hereditary motor and sensory neuropathy (HMSN) are genetically heterogeneous with observed autosomal dominant, autosomal recessive and X-linked dominant inheritance. All three forms are characterized by degeneration of select populations of motor and sensory neurons with accompanying atrophy and degeneration of their axons. Large calibre myelinated fibres are predominantly affected and fibre degeneration and fibre loss progresses from distally to proximally. Attempts of regeneration are noted in all except the severe childhood form. The clinical picture is that of peroneal and distal leg muscle wasting and weakness, distal sensory loss and areflexia. Hand muscles may be severely affected in the autosomal recessive and X-linked dominant forms. Motor and sensory nerve conduction velocities are only moderately slowed and evoked maximum compound motor and sensory amplitudes are reduced according to the degree of fibre loss. The gene locus remains unknown in both the autosomal dominant and autosomal recessive types. For the X-linked dominant HMSN, the gene locus has been mapped closely by linkage analysis to DNA loci in the pericentromeric region of the X-chromosome.

Polyneuropathies in paediatrics

Non-acute polyneuropathies (PNPs) encountered in paediatrics are reviewed. Emphasis is placed on three main groups of conditions: the relatively rare but treatable dysimmune PNP (chronic relapsing dysimmune polyneuropathies, CRDP); the more common hereditary motor/sensory neuropathies (HMSN and HSN); and the often missed symptomatic neuropathies of some heredodegenerative and neurometabolic disorders. Diagnostic procedures are discussed. One conclusion drawn is that so far metabolic screening procedures do not give any diagnostic or aetiological information in HMSN or in HSN, nor in heredoataxias or heredoparaplegias. When a specific neurometabolic disease is suspected from the clinical symptomatology, individually structured investigations are necessary.