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 6 (ALS6) is one of many subtypes of familial ALS. It has been related to mutations in the FUS gene, a protein-coding gene whose product is part of the heterogeneous nuclear ribonucleoprotein complex, which, in turn, regulates gene expression and RNA processing. ALS6 patients suffer from typical ALS, with first symptoms manifesting in adulthood. An association with other neurodegenerative diseases has been reported in isolated cases.
Presentation
ALS6 is clinically indistinguishable from other types of sporadic or familial ALS. First symptoms manifest in adulthood, at a mean age of 44 years [1] [2]. Affected individuals claim muscle weakness, most commonly in the upper limbs and neck, or in the legs. Muscle weakness subsequently spreads to the other limbs and bulbar muscles may become involved. Bulbar palsy preceding limb muscle weakness has repeatedly been described and may be observed in up to one third of ALS6 patients [2], but bulbar involvement doesn't seem to be a constant feature in ALS6: Some patients don't develop dysarthria or dysphagia at any point in time [3].
Vance and colleagues haven't observed any cognitive deficits in ALS6 patients [1], suggesting ALS6 not to be associated with frontotemporal dementia, parkinsonism, or other neurodegenerative disorders. By contrast, Yan et al. reported ALS6 in patients suffering from such diseases [2].
Entire Body System
- Weakness
[…] hand muscles Wasting of hand muscles Weak forearm muscles Wasting of forearm muscles Weak leg muscles Wasting of leg muscles Weak body muscles Wasting of body muscles Weak face muscles Wasting of face muscles Progressive muscle weakness Progressive muscle [checkorphan.org]
Affected individuals claim muscle weakness, most commonly in the upper limbs and neck, or in the legs. Muscle weakness subsequently spreads to the other limbs and bulbar muscles may become involved. [symptoma.com]
Over time, muscle weakness causes affected individuals to lose the use of their hands and arms. Breathing becomes difficult because the muscles of the respiratory system weaken. [ncbi.nlm.nih.gov]
In pedigree 3, all 3 patients had symmetrical, proximal weakness of the upper limbs, followed by symmetrical, proximal weakness of the lower limbs and early respiratory failure. [jamanetwork.com]
- Pain
Please note that severe pain is not a typical symptom of ALS. Who is affected by ALS? Throughout the world, an average of 1 to 2 per 100,000 people are diagnosed with ALS every year. Men are affected more frequently than women. [my.clevelandclinic.org]
There's generally no pain in the early stages of ALS, and pain is uncommon in the later stages. ALS doesn't usually affect your bladder control or your senses. [mayoclinic.org]
Drugs are available to help individuals with pain, panic attacks, and depression Patients with ALS tend to lose weight. The illness itself increases the need for food and calories. [checkorphan.org]
Besides muscle cramps that may cause discomfort, some individuals with ALS may develop painful neuropathy (nerve disease or damage). top How is ALS diagnosed? No one test can provide a definitive diagnosis of ALS. [ninds.nih.gov]
Pain in amyotrophic lateral sclerosis. The Lancet Neurology (2017). doi:10.1016/S1474-4422(16)30358-1 Hardiman, O., Van Den Berg, L. H. & Kiernan, M. C. Clinical diagnosis and management of amyotrophic lateral sclerosis. [mda.org]
- Malnutrition
Many people with ALS experience malnutrition because of reduced food intake due to dysphagia and an increase in their body's energy demands (metabolism) due to prolonged illness. [ncbi.nlm.nih.gov]
Eating problems People with ALS can develop malnutrition and dehydration from damage to the muscles that control swallowing. They are also at higher risk of getting food, liquids or saliva into the lungs, which can cause pneumonia. [mayoclinic.org]
Enteral feeding Enteral feeding prevents the effects of malnutrition, improves patient comfort and may prolong survival. It should be given via a percutaneous endoscopic gastrostomy tube. [anmjournal.com]
- Disability
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As these motor neurons are lost, the muscles they control become weak and then nonfunctional, thus leading to muscle weakness, disability, and eventually death. ALS is the most common form of motor neuron disease. [mda.org]
The disease affected Charles' legs and eventually left him completely disabled. A fund raiser was held to assist Charles and many of his former opponents spoke on his behalf. [en.wikipedia.org]
Disability: ALS Functional Rating Scale (ALSFRS-R), [functional independence measure (FIM), Barthel index] Walking range, pain Manual muscle testing Speech therapy assessment: Dysarthria, swallowing, communication Psychological assessment Nutritional [anmjournal.com]
- Inflammation
Increasing evidence also suggests that various types of glial support cells and inflammation cells of the nervous system may play an important role in the disease. [medicinenet.com]
People with amyotrophic lateral sclerosis are also at increased risk for acute inflammation of the lungs, caused by the inhalation of food or stomach contents (aspiration pneumonia). [rarediseases.org]
Respiratoric
- Pneumonia
They are also at higher risk of getting food, liquids or saliva into the lungs, which can cause pneumonia. A feeding tube can reduce these risks and ensure proper hydration and nutrition. [mayoclinic.org]
Affected individuals also face an increased risk of pneumonia during later stages of the disease. [ninds.nih.gov]
People with amyotrophic lateral sclerosis are also at increased risk for acute inflammation of the lungs, caused by the inhalation of food or stomach contents (aspiration pneumonia). [rarediseases.org]
- Aspiration
People with amyotrophic lateral sclerosis are also at increased risk for acute inflammation of the lungs, caused by the inhalation of food or stomach contents (aspiration pneumonia). [rarediseases.org]
Gastrointestinal
- Dysphagia
Affected individuals may develop slurred speech (dysarthria) and, later, difficulty chewing or swallowing (dysphagia). [ncbi.nlm.nih.gov]
Over the course of the disease, they develop muscle weakness and atrophy in all four limbs, and possibly bulbar palsy associated with dysarthria and dysphagia. [symptoma.com]
Affected individuals may have difficulty swallowing (dysphagia), and speech may be slowed. [rarediseases.org]
- Constipation
Each team member helps the patient cope as much as possible with their handicap under the conditions of greatest comfort. [33] Symptomatic drug therapies Non-specific symptoms: Fatigue, depression and anxiety, constipation, pain, cramp. [anmjournal.com]
Drugs also are available to help individuals with pain, depression, sleep disturbances, and constipation. Pharmacists can give advice on the proper use of medications and monitor a person’s prescriptions to avoid risks of drug interactions. [ninds.nih.gov]
In addition, several patients showed autonomic abnormalities, including chronic intestinal constipation, and sexual dysfunction [33]. [translationalneurodegeneration.biomedcentral.com]
Musculoskeletal
- Muscle Weakness
[…] hand muscles Wasting of hand muscles Weak forearm muscles Wasting of forearm muscles Weak leg muscles Wasting of leg muscles Weak body muscles Wasting of body muscles Weak face muscles Wasting of face muscles Progressive muscle weakness Progressive muscle [checkorphan.org]
Affected individuals claim muscle weakness, most commonly in the upper limbs and neck, or in the legs. Muscle weakness subsequently spreads to the other limbs and bulbar muscles may become involved. [symptoma.com]
Over time, muscle weakness causes affected individuals to lose the use of their hands and arms. Breathing becomes difficult because the muscles of the respiratory system weaken. [ncbi.nlm.nih.gov]
- Muscular Atrophy
Kennedy Syndrome Kennedy's Disease Muscular Atrophy, Spinobulbar Spinal and Bulbar Muscular Atrophy Spinal And Bulbar Muscular Atrophy, X Linked 1 Spinal And Bulbar Muscular Atrophy, X-Linked 1 Spinobulbar Muscular Atrophies Spinobulbar Muscular Atrophy [finto.fi]
Study of 962 patients indicates progressive muscular atrophy is a form of ALS. Neurology (2009). doi:10.1212/WNL.0b013e3181c1dea3 Visser, J. et al. Disease course and prognostic factors of progressive muscular atrophy. Arch. [mda.org]
Lateral Sclerosis Benign Focal Amyotrophy of ALS Infantile Spinal Muscular Atrophy, ALS Juvenile Spinal Muscular Atrophy, Included Kugelberg-Welander Disease Primary Lateral Sclerosis Progressive Bulbar Palsy, Included Spinal Muscular Atrophy, Type ALS [rarediseases.org]
Progressive Muscular Atrophy (PMA) A progressive neurological disease in which the lower motor neurons deteriorate. If the upper motor neurons are not affected within two years, the disease usually remains a pure lower motor neuron disease. [my.clevelandclinic.org]
Very early-onset (generally before 6 years up to adolescence) with prominent distal muscular atrophy and eventually cerebellar ataxia are clues to diagnosis, mimicking spinal muscular atrophy with pyramidal signs and some forms of hereditary distal motor [scielo.br]
- Muscle Twitch
The earliest symptoms include muscle twitching, cramping, stiffness, or weakness. Affected individuals may develop slurred speech (dysarthria) and, later, difficulty chewing or swallowing (dysphagia). [ncbi.nlm.nih.gov]
Symptoms include: Muscle weakness Tripping Falling Loss of motor control in hands and arms Difficulty speaking Difficulty swallowing Difficulty breathing Persistent fatigue Twitching Spasticity Muscle twitching Exaggerated reflexes Muscle cramps Weak [checkorphan.org]
Clinical Signs, Symptoms, and Diagnostics Symptoms and signs associated with these pathological changes include: Muscle fasciculation, more commonly known as muscle twitches Difficulty walking, moving your arms, speaking, and swallowing And, eventually [study.com]
ALS often begins with muscle twitching and weakness in a limb, or slurred speech. Eventually, ALS affects control of the muscles needed to move, speak, eat and breathe. There is no cure for this fatal disease. [mayoclinic.org]
- Muscle Cramp
Symptoms include: Muscle weakness Tripping Falling Loss of motor control in hands and arms Difficulty speaking Difficulty swallowing Difficulty breathing Persistent fatigue Twitching Spasticity Muscle twitching Exaggerated reflexes Muscle cramps Weak [checkorphan.org]
Treatment options include: Medications to relieve painful muscle cramps, excessive salivation and other symptoms. Physical therapy to maintain mobility and ease the discomfort of muscle stiffness, cramps and fluid retention. [my.clevelandclinic.org]
Signs and symptoms might include: Difficulty walking or doing normal daily activities Tripping and falling Weakness in your leg, feet or ankles Hand weakness or clumsiness Slurred speech or trouble swallowing Muscle cramps and twitching in your arms, [mayoclinic.org]
Fasciculations and muscle cramps also occur in benign conditions. [ninds.nih.gov]
Spasticity and muscle cramps may be resolved by muscle relaxants like quinine, levetiracetam, baclofen, or dantrolene. Weakness of the respiratory muscles requires ventilatory assistance. [symptoma.com]
- Muscle Spasm
Baclofen may reduce muscle spasms in some patients. Patients troubled by leg cramps may benefit from quinine compounds. [rarediseases.org]
Psychiatrical
- Anger
The frustration and loss of control may lead to anxiety, anger, depression and controlling behavior. [anmjournal.com]
Neurologic
- Dysarthria
Over the course of the disease, they develop muscle weakness and atrophy in all four limbs, and possibly bulbar palsy associated with dysarthria and dysphagia. [symptoma.com]
Affected individuals may develop slurred speech (dysarthria) and, later, difficulty chewing or swallowing (dysphagia). [ncbi.nlm.nih.gov]
Patients then develop motor neuron degeneration leading to facial muscle spasticity, spastic dysarthria, and spastic gait. Some patients are reported to have uncontrolled laughter and weeping (pseudobulbar syndrome). [orpha.net]
[…] perish, the ventral roots thin and the limb, tongue, and oropharynx muscles become amyotrophic.1 However, one-third of patients experience bulbar disease, manifesting as challenges with speaking, chewing, or swallowing.1 Signs of bulbar disease include dysarthria [ajmc.com]
- Paresis
After approximately 3 years, he noticed weakness of the shoulders, and a symmetrical proximal paresis of the upper limbs was found on neurologic examination. [jamanetwork.com]
Spastic paresis could be present at the beginning or in the fully developed stage of the disease. [intechopen.com]
The D90A-homozygous mutation is associated with slowly progressive paresis in the legs that gradually spreads up to the arms, thoracic and bulbar musculature, with atypical non-motor features such as ataxia, neuralgic, aching pain, heat sensations, and [translationalneurodegeneration.biomedcentral.com]
ALS HNRNPA1 (Heterogeneous Nuclear Ribonucleoprotein A1; 12q13.13) – 2013 AD ALS20, IBM with early-onset Paget disease without FTD type 3 DCTN1 (Dynactin 1; 2p13.1) – 2003 AD ALS, Perry syndrome, Distal hereditary motor neuronopathy with vocal paresis [scielo.br]
- Limb Weakness
The beginning of symptoms was weakness in upper limbs, without involvement of lower limbs or bulbar functions. [intechopen.com]
Workup
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 [4] [5] [6]. Currently, revised El Escorial criteria are applied in most clinical trials. Those criteria are as follows [4]:
- Clinical evidence of upper motor neuron degeneration
- Clinical, electrophysiological, or neuropathological evidence of lower motor neuron degeneration
- Disease progression, spread of symptoms and signs
- Absence of electrophysiological or pathological evidence of other diseases that may explain neurological findings
- Absence of imaging evidence of other diseases that may explain neurological findings
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 [4]:
- Clinically definite ALS requires the presence of upper and lower motor neuron signs in at least three out of four regions
- Clinically probable ALS is diagnosed with upper and lower motor neuron signs in at least two out of four regions, and some upper motor neuron signs rostral to lower motor neuron signs
- Clinically probable if laboratory-supported ALS is defined as the presence of upper and lower motor neuron signs in one region only, or the presence of only upper motor neuron signs in one region and lower motor neuron signs in at least two regions, with lower motor signs generally being present on electromyography
- Clinically possibly ALS implies the presence of upper and lower motor neuron signs in one region only, or the presence of only upper motor neuron signs in at least two regions, or the presence of lower motor neuron signs rostral to upper motor neuron signs, if supporting laboratory results cannot be provided
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 [4].
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 [7] [8]. Additionally, ALS patients known to carry mutations that possibly predispose for frontotemporal dementia or parkinsonism - as is the case with FUS mutations - may be referred for neuropsychological tests [9] [10].
Treatment
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 [11]. The application of α-tocopherol has been proposed as a complementary measure to slow down disease progression in milder cases [12]. 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 [12] [13]:
- Bulbar palsy results in speech disturbances and swallowing difficulties and largely affects the patients' quality of life. Therefore, they should be offered support by speech therapists and nutritionists. Modern technical devices enable ALS patients to express their thoughts even if they can only provide minimal input. Also, it may be helpful to mash solid foods to facilitate their intake by dysphagic patients, but most patients eventually require a gastrostomy tube.
- Occupational and physical therapy are required to deal with limited mobility. At the same time, orthopedic devices and wheelchairs should be provided to improve mobility and autonomy.
- Spasticity and muscle cramps may be resolved by muscle relaxants like quinine, levetiracetam, baclofen, or dantrolene.
- Weakness of the respiratory muscles requires ventilatory assistance.
- Finally, ALS patients should be offered psychological support. Some patients develop depressions and have to be treated with antidepressants.
If ALS6 patients suffer from associated neurodegenerative disorders such as dementia or parkinsonism, these should be treated according to the respective guidelines. Unfortunately though, they can neither be cured at this moment.
Prognosis
Progressive muscle weakness and atrophy leads to respiratory paralysis and death within three and a half years of symptom onset [2]. Thus, the mean duration of ALS6 doesn't differ from that of ALS in general: Mean survival times of ALS patients were calculated to be three to four years [14].
Etiology
In 2009, two independent groups of researchers have described familial ALS related to mutations of the FUS gene on chromosome 16 - a total of thirteen mutations have been identified in the respective studies [1] [3]. Other mutations have been identified later on and at this time, 58 ALS-associated mutations of the FUS gene are known [15]. The FUS gene is also referred to as FUS/TLS or fused in sarcoma/translated in liposarcoma gene [3]. Its gene product generally locates to the nucleus and has been identified as part of the heterogeneous nuclear ribonucleoprotein complex. Kwiatkowski and colleagues have shown mutant forms of the protein to accumulate within the cytosol of neurons [3]. Similarly, Vance et al. have observed cytosolic inclusions and postulated that anomalies regarding the regulation of transcription, RNA splicing and transport account for ALS6-related neurodegeneration [1].
Of note, FUS mutations have been detected in patients suffering from apparently sporadic ALS [2] [16]. This fact supports the hypothesis of ALS being a multifactorial disease with mutations of the FUS gene being one of many variables that may predispose an individual for this motor neuron disease. Presumably, additional genetic and environmental factors determine whether someone carrying FUS mutations does develop ALS or not, and whether the course of the disease corresponds to what would be expected for ALS6.
Epidemiology
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 [14]. By contrast, individuals affected by ALS6 were reported to manifest first symptoms at a mean age of 44 years [1] [2]. 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 [14]. About 10% of all those cases are familial. Familial ALS is generally inherited in an autosomal dominant manner, but the mode of inheritance has not yet been definitively clarified for ALS6: Both homozygous mutations and heterozygous mutations have been associated with this form of ALS [3]. Additionally, FUS mutations have reduced penetrance [3]. By now, FUS-related ALS has been described in Caucasian, Asian, and African patients [2].
Pathophysiology
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 misfolded proteins. Sequence anomalies, e.g., of genes like FUS, 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 [17].
As for ALS6 and mutated FUS proteins, their cytosolic accumulation has been shown by different authors [1] [3]. Common FUS mutations affect the protein's C-terminal domain and this domain has been found to be crucial for its nuclear localization. Mutated proteins don't locate to the nucleus, form stress granules in the cytosol, and exert neurotoxic effects [18].
Prevention
No recommendations can be given to prevent the onset of sporadic ALS, other than avoiding certain risk factors [14]. By contrast, genetic analyses may facilitate the identification of carriers and as-of-yet asymptomatic patients in families affected by familial ALS [7]. Prenatal diagnoses may become feasible if the disease can be related to well-defined DNA sequence anomalies, but this does not yet apply to ALS6.
Summary
ALS is the most common motor neuron disease. ALS patients may be genetically predisposed to develop the disease, and distinct genes have been associated with its familial form. One of those genes is the FUS gene, which encodes for a nuclear RNA-binding protein. ALS linked to mutations in the FUS gene has been designated ALS6. Presumably, mutations of the FUS gene result in the accumulation of cytotoxic granules within neurons, but little is actually known about the etiology and pathogenesis of ALS6 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, and this also applies to ALS6. However, the most common clinical presentation of ALS6 is that of "pure ALS", i.e., in early stages of the disease, patients experience muscle weakness, particularly in their arms or legs. Over the course of the disease, they develop muscle weakness and atrophy in all four limbs, and possibly 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 to amyotrophy.
Diagnosis of ALS relies on well-defined diagnostic criteria and is mainly clinical, with the identification of ALS6 requiring additional genetic analyses. Mean survival times are three to four 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.
Patient Information
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 are families whose members present mutations in a gene called FUS. FUS-related ALS has later been designated amyotrophic lateral sclerosis 6 (ALS6).
With regards to clinical presentation, diagnosis, treatment, and prognosis, ALS6 doesn't differ from classical ALS. Similar to other forms of ALS, ALS6 may be associated with neurodegenerative disorders like frontotemporal dementia or parkinsonism, but few such cases have been reported to date.
References
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