Co-morbid Conditions of SMA
Spinal muscular atrophy (SMA) is a rare genetic condition characterized by progressive muscle weakness and atrophy, mainly affecting motor function, but often also causing speaking, swallowing, and breathing problems, along with other symptoms.
SMA has co-morbidities relating to various aspects of the disease itself, from sleeping disorders to cardiac disease. The following are the known co-morbid conditions that can occur with SMA.
Abnormal Fatty Acid Oxidation
Fatty acids are an important source of cellular energy, and deficiencies in fatty acids and their oxidation can lead to a variety of health issues, including liver dysfunction, cardiomyopathy, skeletal myopathy, and hepatic disease. Cancer studies have shown that excessive fatty acid oxidation can induce muscle atrophy, and research has shown that SMA is associated with abnormal fatty acid oxidation.
In patients with SMA, tissue levels of SMN1 protein are reduced in heart tissues, and numerous mouse models of SMA exhibit cardiac developmental abnormalities which together suggest that low SMN1 protein is a possible risk factor and potential cause of heart defects.
Enuresis and Urinary Incontinence
There is evidence to suggest that the rate of enuresis and urinary incontinence in children and adolescents with SMA may be much higher than the average child. Urinary incontinence is the involuntary leakage of urine either continuously or intermittently. It is further divided into daytime incontinence and enuresis, i.e., incontinence that occurs exclusively during periods of sleep. Nocturia is waking at night to urinate.
Eosinophilic oesophagitis (EoE) is a chronic immune/antigen-mediated oesophageal disease that involves oesophageal dysfunction and occurs 3 times more often in men than in women. The main symptoms associated with EoE in children include feeding difficulties, abdominal pain, and vomiting. In adolescents and adults, symptoms include dysphagia and food impaction. The antigens mediating the disease are primarily food-based antigens.
Evidence of a primary chronic pancreatic pathology in patients with SMA is evolving as patients survive to older ages and as researchers expand the scope of SMA beyond neurodegeneration. Pancreatic dysfunction in SMA can manifest acutely. Acute pancreatitis without an obvious etiology occurs rarely in patients with type 1 SMA.
Progressive Myoclonic Epilepsy
SMA that co-occurs with progressive myoclonic epilepsy (PME) is a rare inherited syndrome referred to as SMA-PME. It is caused by a mutation in the ASAH1 gene, which is a gene that encodes acid ceramidase. ASAH1 is located on chromosome 8, and the mutation associated with SMA-PME is a missense mutation in exon 2.
Those with SMA often suffer from sleep disorders, but the specific reasons for sleep disturbances vary. Breathing disorders experienced during sleep, as well as difficulty falling asleep and staying asleep, were the most commonly found sleep issues in those with SMA. Excessive sleepiness and night sweats were other frequently experienced factors disturbing sleep.