Amyotrophic lateral sclerosis (ALS) is a progressive and generally fatal motor neuron disease. Most cases are sporadic, but high familial incidence is observed occasionally. Amyotrophic lateral sclerosis 7 (ALS7) may be one of many subtypes of familial ALS, but it remains a matter of discussion whether or not ALS7 constitutes an individual entity. It has been related to chromosomal locus 20ptel-p13. Those individuals who have been shown to have the respective genotype suffered from typical ALS with first symptoms manifesting in adulthood. ALS7 may be inherited in an autosomal dominant manner.
The study published by Sapp and colleagues doesn't include details regarding the clinical presentation of ALS7 patients. However, the authors mention that all their patients met with generally accepted diagnostic criteria as described in the following section . Accordingly, ALS7 patients are expected to develop limb muscle weakness in adulthood. Muscle weakness may initially be limited to one or two extremities, but subsequently spreads to the other limbs. As the disease progresses, ALS patients often develop bulbar palsy, which manifests as dysarthria and dysphagia, and symptomatic upper motor neuron disease:
ALS diagnosis relies on the identification of upper motor neuron and lower motor neuron signs, to be observed in patients suffering from a progressive neurodegenerative disease that cannot be explained by other conditions. To facilitate ALS diagnosis, diagnostic criteria have been defined on various occasions   . Currently, revised El Escorial criteria are applied in most clinical trials. Those criteria are as follows :
Furthermore, the central nervous system is divided into four regions, namely the bulbar, cervical, thoracic and lumbosacral region as indicated in the previous paragraph. The presence of symptoms related to the function of any of those four regions allows for a more precise diagnosis of clinically definite, clinically probable, clinically probable if laboratory-supported, and clinically possible ALS :
A positive family history of ALS augments the certainty of diagnosis and may even justify the diagnosis of clinically definite ALS if the respective criteria are not completely fulfilled .
Even though molecular biological analyses are not required for the diagnosis of ALS, they are necessary to determine the subtype. In fact, the identification of sequence anomalies may accelerate the diagnostic process. Genetic analyses also provide both physicians and scientists with an appropriate tool to identify carriers and family members at risk, and to promote research  .
There is no cure, and disease progression can hardly be halted. Riluzole is the only pharmacological compound approved for ALS therapy; it is assumed to reduce glutamate toxicity. It has been reported to increase survival times and to delay the onset of life-threatening symptoms such as laryngospasm and respiratory paralysis, but its efficacy is very limited . The application of α-tocopherol has been proposed as a complementary measure to slow down disease progression in milder cases . Otherwise, only palliative treatment can be provided. In this context, ALS patients benefit from a multidisciplinary approach that aims at maintaining their ability to cope with everyday life and to communicate with their fellows for as long as possible  :
In 2003, Sapp and colleagues have studied sixteen pedigrees of US families known to be affected by familial ALS, but without evidence for mutations in the SOD1 gene . Of note, mutations in the SOD1 gene presumably account for 20% of all cases of familial ALS . In one of those families, the disease status of family members has been linked to chromosomal locus 20ptel . In detail, the locus has been found to span the region from the telomere of the short arm of chromosome 20 to marker D20S199 on 20p13, which corresponds to about 1 Mbp . The locus may comprise 20 to 24 genes. Data regarding the role of locus 20ptel-p13 in ALS7 pathogenesis are not available; genes in this locus that may be involved in the development of ALS have not yet been identified. Given the fact that chromosomal locus 20ptel-p13 has never again been related to ALS, doubts may arise as to whether ALS7 should be considered an individual entity or not .
Besides genetic factors, environmental influences are assumed to play a major role in ALS pathogenesis. With regards to such environmental influences, the following have been identified and confirmed as risk factors for ALS :
ALS is the most common motor neuron disease in adults; it affects both men and women. ALS patients' mean age at symptom onset is 60 years . With regards to the ALS7 patients described by Sapp et al., their mean age at the appearance of first symptoms was 56 years . The global incidence of ALS has been estimated to 1-2.6 per 100,000 people per year, and its prevalence amounts to 6 per 100,000 inhabitants . About 10% of all those cases are familial, but ALS7 has only ever been described in two members of the same family .
Familial ALS is generally inherited in an autosomal dominant manner and this mode of inheritance has also been postulated for ALS7: Samples were obtained from 25 members of said family, two of whom were suffering from ALS. They were siblings. They had thirteen more siblings, none of whom showed symptoms of ALS. By contrast, one third-degree relative and one distant relative had developed ALS previously . Because neither of the affected individuals' parents has experienced ALS-related complaints despite one of them being an obligate heterozygote carrier of the ALS7-associated locus, incomplete penetrance may be assumed .
Despite extensive research, the pathophysiology of ALS remains poorly understood. The death of motor neurons is the hallmark of the disease and entails muscle weakness and atrophy, but its causes could not yet be clarified. Neuronal death has been speculated to be due to the accumulation of protein aggregates which, in turn, consist of abnormal proteins. Sequence anomalies, e.g., of regulatory or protein-coding genes on chromosomal locus 20ptel-p13, may be the cause of irregularities in the amino acid sequence, post-translational modification and intracellular transport of any protein, may alter their physical properties, their propensity to bind to specific targets, and their susceptibility to degradation .
No recommendations can be given to prevent the onset of sporadic ALS, other than avoiding the risk factors mentioned above. By contrast, genetic analyses may facilitate the identification of carriers and as-of-yet asymptomatic patients in families affected by familial ALS . Prenatal diagnoses may become feasible if the disease can be related to well-defined DNA sequence anomalies, but this does not yet apply to ALS7. Further research is required to identify those genes on chromosomal locus 20ptel-p13 that predispose for the development of this type of ALS.
ALS is the most common motor neuron disease. ALS patients may be genetically predisposed to develop the disease, and distinct chromosomal loci have been associated with its familial form. While studying the background of ALS in a five-generation family originating from the United States, Sapp et al. found the disease to be linked to chromosomal locus 20ptel-p13 . Although such linkage has never been detected in another family, ALS linked to this locus has later been designated ALS7 . Presumably, mutations of genes in locus 20ptel-p13 confer susceptibility to environmental risk factors that eventually trigger disease onset in adulthood . But even though much has been speculated, very little is actually known about the etiology and pathogenesis of ALS7 and other types of ALS, other than that it is characterized by the death of motor neurons in the cortex, brain stem, and spinal cord. The disease follows a progressive course and ultimately leads to death by respiratory failure.
Familial ALS may be associated with frontotemporal dementia, but this has not yet been described for ALS7. The clinical presentation of ALS7 is that of "pure ALS", i.e., in early stages of the disease, patients experience muscle weakness in any of their extremities. Over the course of the disease, they develop muscle weakness and atrophy in all four limbs, and probably bulbar palsy associated with dysarthria and dysphagia. Besides these lower motor neuron signs, upper motor neuron signs are characteristic of ALS: ALS patients suffer from hyperreflexia and present with an increased muscle tone, and while those complaints are initially limited to certain body regions, they spread in a similar manner as amyotrophy.
Diagnosis of ALS relies on well-defined diagnostic criteria and is mainly clinical, with the identification of ALS7 requiring additional genetic analyses. Mean survival times don't exceed three years and patients should be treated by a multidisciplinary team to preserve life quality for as long as possible, despite the fact that there is no cure for this disease.
Amyotrophic lateral sclerosis (ALS) is a progressive motor neuron disease that typically manifests in adulthood. Little is known about the causes of ALS, but at least a minor proportion of ALS patients seems to be genetically predisposed. This condition is reflected in an increased familial incidence, i.e., relatives of an ALS patient carrying certain gene defects are much more likely to develop the disease than the general population. In this context, ALS has been associated with distinct chromosome and gene anomalies. For instance, there is a US family whose members present sequence anomalies on the short arm of chromosome 20. This particular condition has later been designated amyotrophic lateral sclerosis 7 (ALS7).
With regards to clinical presentation, diagnosis, treatment, and prognosis, ALS7 doesn't differ from classical ALS.