N-acetyl-beta-hexosaminidase beta locus defect and juvenile motor neuron disease: a case study

A patient with partial deficiency of N-acetyl-beta-hexosaminidase (Hex) developed a progressive motor neuron syndrome beginning at age 7, characterized by dysarthria, muscle wasting, fasciculations, and pyramidal tract dysfunction. Minor clinical features have included tremor and late distal sensory abnormalities. Rectal biopsy at age 24 demonstrated membranous cytoplasmic bodies in submucosal ganglion cells. Biochemical evaluation revealed nearly absent Hex B activity in serum, leukocytes, and fibroblasts, with partial Hex A activity in serum and leukocytes, and low normal Hex A activity in fibroblasts. Motor neuron disease can be a presentation of a Hex beta locus defect, in addition to the previously recognized Hex alpha locus defects.