The reduction of androgen receptor mRNA in motoneurons of X-linked spinal and bulbar muscular atrophy

[Molecular and genetic analysis of spinocerebellar ataxia type 10 (SCA10)]

Spinocerebellar ataxia type 10 (SCA10) is a dominantly inherited neurodegenerative disease caused by expansion of the ATTCT pentanucleotide repeat in intron 9 of a novel gene, ATXN10, on chromosome 22q13.3. It is clinically characterized by progressive ataxia, seizures, and anticipation, which can vary within and between families. The length of the expanded ATTCT repeats is highly unstable on paternal transmission and shows a variable degree of somatic and germline instabilty, revealing complex SCA10 genetic mechanisms. Moreover, the purity of the expanded repeat element may be a disease modifier. ATTCT repeats have been recently shown to form unpaired DNA structure and may serve as an aberrant DNA replication origin, potentially contributing to repeat instability and cell death. How this untranslated ATTCT expansion leads to neurodegeneration has been still controversial. We discuss several possible pathogenic mechanisms for SCA10, and growing number of evidence indicates a gain-of-function RNA mechanism, similar to the myotonic dystrophies caused by non-coding CTG or CCTG repeat expansions.

Kennedy's disease: pathogenesis and clinical approaches

Kennedy's disease, also known as spinal and bulbar muscular atrophy, is a progressive degenerative condition affecting lower motor neurons. It is one of nine neurodegenerative disorders caused by a polyglutamine repeat expansion. Affecting only men, Kennedy's disease is the only one of these conditions that follows an X-linked mode of inheritance. The causative protein in Kennedy's disease, with a polyglutamine expansion residing in the first N-terminal domain, is the androgen receptor. Research in this field has made significant advances in recent years, and with the increased understanding of pathogenic mechanisms, feasible approaches to treatments are being investigated. In Kennedy's disease research, the most significant issue to emerge recently is the role of androgens in exacerbating the disease process. On the basis of animal experiments, a viable hypothesis is that higher circulating levels of androgens in men could trigger the degeneration of motor neurons causing this disease, and that lower levels in heterozygous and homozygous women are protective. This is a major issue, as treatment of individuals affected by Kennedy's disease with testosterone has been considered a reasonable therapy by some neurologists. The rationale behind this approach relates to the fact that Kennedy's disease is accompanied by mild androgen insensitivity. It was therefore believed that treatment with high doses of testosterone might compensate for this loss of androgen action, with the added benefit of preventing muscle wasting. The current review provides an overview of recent advances in the field of Kennedy's disease research, including approaches to treatment.

X-linked spinal and bulbar muscular atrophy without proximal atrophy

We report on a case of genetically proven X-linked spinal and bulbar muscular atrophy (X-SBMA) with prominent distal muscle atrophy and without proximal muscle involvement. The patient was a 35-year-old man who had a history of slow progressive hand and distal leg muscle weakness and wasting for 10 years. Motor nerve conduction velocities were normal with reduced compound muscle action potential amplitudes of hand and foot muscles. Sensory action potential amplitudes were small. Needle EMG revealed a chronic partial denervation with reduced interference in hand and distal leg muscles but with normal heading in all tested proximal muscles. Genetic studied showed an expansion of CAG repeat in the first exon of the androgen receptor gene, which suggests diagnosis of X-SBMA. The importance of genetic studies in this patient with unusual clinical presentation is emphasized.

Epidemiological survey of X-linked bulbar and spinal muscular atrophy, or Kennedy disease, in the province of Reggio Emilia, Italy

Commencing with the work carried out during the epidemiological survey of amyotrophic lateral sclerosis in the period 1980-1992 and the pathology follow-up, we carried out a perspective incidence, prevalence and mortality survey of X-linked bulbar and spinal muscular atrophy (X-BSMA) in the province of Reggio Emilia in Northern Italy. Based on 11 patients (eight familial and three sporadic cases), the mean incidence per year for the period 1980 through 1997, as evaluated at the onset of symptoms, was 0.09 cases/100,000 for the total population and 0.19 cases/100,000 for the male population. On December 31, 1997, the prevalence rate was 1.6/100,000 for the total population and 3.3/100,000 for the male population. In the 18-year period of 1980-1997, the average yearly mortality rate was: 0.03 cases/100,000 per year for the total population and 0.06 cases/ 100,000 for the male population. The average age at onset was 44.8 +/- 10.1, and the average survival period was 27.3 +/- 2.3 years. The average age of the prevalence day was 58.9 +/- 14.9, and the average age at death was 71.3 +/- 4.7 years. Whereas the incidence rate of X-BSMA in the province of Reggio Emilia is 16 times lower that of amyotrophic lateral sclerosis (ALS), the incidence rate of progressive bulbar palsy in the male population is only slightly higher than X-BSMA; and the prevalence rate of ALS for males is two times the prevalence rate for X-BSMA, with overlapping of confidence intervals. X-BSMA is a rare disease, which is probably under-diagnosed, but due to the long survival period of this disease its frequency is not negligible. Because of the presence of sporadic cases or non-evident familial cases, it is appropriate to consider this diagnostic possibility in making a diagnosis of ALS in patients in whom lower motor neuron dysfunction or bulbar onset predominates.