[Does the brain influence the muscular development of the human fetus? Evidence in 21 cases].

The importance of suprasegmental cerebral influence on developing human fetal muscle is less well understood than the control of histochemical differentiation of muscle by the motor neuron. Muscle biopsies of 21 hypotonic infants and children with nonprogressive congenital lesions of the cerebellum and/or brainstem were studied by histochemical methods. Two neonates who died with severely dysplastic brains and no descending motor tracts had normal muscle. The others, particularly those with cerebellar hypoplasia, had delayed muscle maturation, selective predominance of type I or II muscle fibres or disproportion in fibre sizes. It is concluded that the motor unit is capable of developing normally without suprasegmental influence, but that an abnormal balance of descending impulses may alter histochemical differentiation of fetal muscle. The small 'subcorticospinal' pathways arising in the brainstem probably are more influential than the larger corticospinal tract because of later myelination in the latter. The muscle biopsy thus serves to provide evidence of suprasegmental disease in infantile hypotonia.