Clinicopathological phenotype of ALS with a novel G72C SOD1 gene mutation mimicking a myopathy.

A 71-year-old woman with a family history of amyotrophic lateral sclerosis (ALS) was investigated for symmetrical, proximal limb and abdominal muscle weakness. Initial examination showed mild proximal muscle weakness in the arms and legs, slightly elevated serum creatine kinase (CK) level, and normal electromyographic (EMG) findings. A myopathy was the presumed diagnosis. Over the next year, weakness became severe and tendon reflexes became unelicitable; no upper motor signs were present. EMG then showed acute and chronic denervation and a muscle biopsy showed target fibers and grouped atrophy. DNA analysis revealed a G72C CuZn-superoxide dismutase (SOD1) mutation. Fasciculations were absent throughout the disease. The patient died 53 months after symptom onset and autopsy revealed loss of lower motor neurons (LMN) and SOD1-positive inclusions. This case expands the phenotypic spectrum of ALS associated with SOD1 mutations to include presenting features that mimic a myopathy.

The physiological basis of conduction slowing in ALS patients homozygous for the D90A CuZn-SOD mutation.

Familial amyotrophic lateral sclerosis (ALS) with the autosomal-recessively inherited D90A CuZn-superoxide dismutase (CuZn-SOD) mutation is characterized by a stereotypic slowly progressive, distinctive phenotype and very slow central motor conduction. To determine the basis of this slowing, we assessed corticomotoneuronal function using peristimulus time histograms (PSTHs) in 8 ALS patients homozygous for the D90A CuZn-SOD mutation. The results were compared with findings in 10 patients with multiple sclerosis (MS), in which slowing of central motor conduction is common, and 11 healthy subjects. PSTHs were constructed from 3-7 different, voluntarily recruited motor units recorded in each patient from the extensor digitorum communis muscle (EDC). In D90A and MS patients, the stimulus threshold, onset latency, number of excess bins, duration, amplitude, and synchrony of the primary peak differed significantly from controls (P < 0.0004). The mean onset latency of the primary peak in D90A patients was 35.3 ms, compared to 23.6 ms for MS patients and 19.3 ms for normal subjects (P < 0.0001). In the D90A patients, the onset latencies of the primary peak had a bimodal distribution, whereas in MS the distribution showed a continuum. Loss of synchrony was similar in D90A and MS patients, but the threshold, number of excess bins, and duration differed significantly (P < 0.0057), which suggests that either axonal loss or demyelination can result in delayed and desynchronized primary peaks. We propose that conduction slowing in the D90A homozygotes results from selective loss of fast-conducting large pyramidal cells with preservation of slow-conducting mono- or polysynaptic corticomotoneuronal connections.

Preserved slow conducting corticomotoneuronal projections in amyotrophic lateral sclerosis with autosomal recessive D90A CuZn-superoxide dismutase mutation.

Recently, a subgroup of the amyotrophic lateral sclerosis (ALS) syndrome associated with mutations in the gene encoding the free radical scavenging enzyme CuZn-superoxide dismutase (CuZn-SOD, SOD1) has been identified. Some 67 different mutations have been reported worldwide to date, comprising about one-fifth of familial ALS cases in the populations studied. The autosomal recessively inherited D90A CuZn-SOD mutation has been associated with a very slowly progressive, clinically distinct phenotype, and is neurophysiologically characterized by very slow central motor conduction. It is not known which physiological and/or biochemical mechanisms are responsible for the different clinical course. To delineate ALS associated with this particular CuZn-SOD mutation from ALS without mutations, we performed a detailed neurophysiological study of the corticomotoneuronal function using peristimulus time histograms (PSTHs) in eight ALS patients homozygous for the D90A CuZn-SOD mutation. The results were compared with those obtained in 12 non-hereditary ALS patients and 11 healthy subjects. PSTHs were constructed from three to seven different, voluntarily recruited motor units of the extensor digitorum communis muscle (EDC) in each patient. The onset latency, number of excess bins, duration and synchrony of the primary peak were analysed. All measurements differed significantly between healthy controls and the D90A patients (P < 0.0007). The mean onset latency of the primary peak in D90A patients was 35.3 ms, compared with 24.2 ms for non-hereditary ALS patients and 19.3 ms for normal subjects (P < 0.0000). Delayed primary peaks in the D90A patients were desynchronized and characteristically preceded by a marked suppression phase. This suppression phase was not seen in non-hereditary ALS patients. We conclude that the mainly slow conducting and/or polysynaptic corticomotoneuronal connections are preserved in the D90A homozygous cases, and that the cortical and possibly spinal inhibitory circuitry is preserved. These events may partially protect the motor neurons, slowing down the degenerative process.