These issues more commonly occurs while asleep, when muscles are more relaxed. Swallowing muscles in the pharynx can be affected, leading to aspiration coupled with a poor coughing mechanism increases the likelihood of infection/pneumonia. Mobilizing and clearing secretions involve manual or mechanical chest physiotherapy with postural drainage, and manual or mechanical cough assistance device. To assist in breathing, Non-invasive ventilation (BiPAP) is frequently used and tracheostomy may be sometimes performed in more severe cases; both methods of ventilation prolong survival to a comparable degree, although tracheostomy prevents speech development. Nutrition
The more severe the type of SMA, the more likely to have nutrition related health issues. Health issues can include difficulty in feeding, jaw opening, chewing and swallowing. Individuals with such difficulties can be at increase risk of over or undernutrition, failure to thrive and aspiration. Other nutritional issues, especially in individuals that are non-ambulatory (more severe types of SMA), include food not passing through the stomach quickly enough, gastric reflux, constipation, vomiting and bloating. Therein, it could be necessary in SMA type I and people with more severe type II to have a feeding tube or gastrostomy. Additionally, metabolic abnormalities resulting from SMA impair β-oxidation of fatty acids in muscles and can lead to organic acidemia and consequent muscle damage, especially when fasting. It is suggested that people with SMA, especially those with more severe forms of the disease, reduce intake of fat and avoid prolonged fasting (i.e., eat more frequently than healthy people) as well as choosing softer foods to avoid aspiration.
Consequently, denervated muscles undergo progressive atrophy (waste away).Muscles of lower extremities are usually affected first, followed by muscles of upper extremities, spine and neck and, in more severe cases, pulmonary and mastication muscles. Proximal muscles are always affected earlier and to a greater degree than distal muscles.The severity of SMA symptoms is broadly related to how well the remaining SMN2 genes can make up for the loss of function of SMN1. This partly depends on the number of copies of the SMN2 gene present on the chromosome. Whilst healthy individuals usually carry two SMN2 gene copies, people with SMA can have anything between 1 and 5 (or more) of them; the greater the number of SMN2 copies, the milder the disease severity. Thus, most SMA type I babies have one or two SMN2 copies; people with SMA II and III usually have at least three SMN2 copies; and people with SMA IV normally have at least four of them. However, the correlation between symptom severity and SMN2 copy number is not absolute and there seem to exist other factors affecting the disease phenotype.Spinal muscular atrophy is inherited in an autosomal recessive pattern, which means that the defective gene is located on an autosome. Two copies of the defective gene – one from each parent – are required to inherit the disorder: the parents may be carriers and not personally affected.