remaining patients. genetic testing is usually carried out using a blood sample, and mlpa is one of more frequently used genetic testing techniques, as it also allows establishing the number of smn2 gene copies, which has clinical importance. symptomatically, sma can be diagnosed with a degree of certainty only in children with the acute form who manifest a progressive illness with paradoxical breathing, bilateral low muscle tone and absent tendon reflexes. early diagnosis early diagnosis of sma, at the asymptomatic stage of the disease, allows to introduce causative therapies early enough to prevent the manifestation of symptoms. preimplantation testing preimplantation genetic diagnosis can be used to screen for sma-affected embryos during in-vitro fertilisation. prenatal testing prenatal testing for sma is possible through chorionic villus sampling, cell-free fetal dna analysis and other methods. newborn screening routine newborn screening for sma is becoming increasingly commonplace in developed countries, given the availability of causative treatments that are most effective at the asymptomatic stage of the disease. in 2018, newborn screening for sma was added to the us list of recommended newborn screening tests and as of april 2020 it has been adopted in 39 us states. as of february 2023, sma screening has been incorporated in national newborn screening programmes in around 15 countries and pilot projects are under way in further countries. carrier testing those at risk of being carriers of smn1 deletion, and thus at risk of having offspring affected by sma, can undergo carrier analysis using a blood or saliva sample. the american college of obstetricians and gynecologists recommends all people thinking of becoming pregnant be tested to see if they are a carrier. the carrier frequency of sma is comparable to other disorders like thalassemia and in a north indian cohort has been found to be 1 in 38. however, genetic testing will not be able to identify all individuals at risk since about 2% of cases are caused by de novo mutations and 5% of the normal population have two copies of smn1 on the same chromosome, which makes it possible to be a carrier by having one chromosome with two copies and a second chromosome with zero copies. this situation will lead to a false negative result, as the carrier status will not be correctly detected by a traditional genetic test. management the management of sma varies based upon the severity and type. in the most severe forms (types 0/1), individuals have the greatest muscle weakness requiring prompt intervention. whereas the least severe form (type 4/adult onset), individuals may not seek the certain aspects of care until later (decades) in life. while types of sma and individuals among each type may differ, therefore specific aspects of an individual's care can differ. medication nusinersen (marketed as spinraza) is used to treat spinal muscular atrophy. it is an antisense nucleotide that modifies the alternative splicing of the smn2 gene. it is given directly to the central nervous system using an intrathecal injection. nusinersen prolongs survival and improves motor function in infants with sma. it was approved for use in the us in 2016, and for use in the eu in 2017. onasemnogene abeparvovec (marketed as zolgensma) is a gene therapy treatment which uses self-complementary adeno-associated virus type 9 (scaav-9) as a vector to deliver the smn1 transgene. the therapy was first approved in the us in may 2019 as an intravenous formulation for children below 24 months of age. approval in the european union, japan and other countries followed, albeit often with different approval scopes. risdiplam (marketed as evrysdi) is a medication taken by mouth in liquid form. it is a pyridazine derivative that works by increasing the amount of functional survivor motor neuron protein produced by the smn2 gene through modifying its splicing pattern. risdiplam was first approved for medical use in the united states in august 2020 and has since been approved in over 30 countries. breathing the respiratory system is the most common system to be affected and the complications are the leading cause of death in sma types 0/1 and 2. sma type 3 can have similar respiratory problems, but it is more rare. complications arise due to weakened intercostal muscles because of the lack of stimulation from the nerve. the diaphragm is less affected than the intercostal muscles. once weakened, the muscles never fully recover the same functional capacity to help in breathing and coughing as well as other functions. therefore, breathing is more difficult and pose a risk of not getting enough oxygen/shallow breathing and insufficient clearance of airway secretions. these issues more commonly occur 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. during an acute illness, especially in children, nutritional problems may first present or can exacerbate an existing problem (example: aspiration) as well as cause other health issues such as electrolyte and blood sugar disturbances. orthopaedics skeletal problems associated with weak muscles in sma include tight joints with limited range of movement, hip dislocations, spinal deformity, osteopenia, an increase risk of fractures and pain. weak muscles that normally stabilize joints such as the vertebral column lead to development of kyphosis and/or scoliosis and joint contracture. spine fusion is sometimes performed in people with sma i/ii once they reach the age of 8–10 to relieve the pressure of a deformed spine on the lungs. furthermore, immobile individuals, posture and position on mobility devices as well as range of motion exercises, and bone strengthening can be important to prevent complications. people with sma might also benefit greatly from various forms of physiotherapy and occupational therapy. orthotic devices can be used to support the body and to aid walking. for example, orthotics such as afos (ankle foot orthoses) are used to stabilise the foot and to aid gait, tlsos (thoracic lumbar sacral orthoses) are used to stabilise the torso. assistive technologies may help in managing movement and daily activity and greatly increase the quality of life. other although the heart is not a matter of routine concern, a link between sma and certain heart conditions has been suggested. children with sma do not differ from the general population in their behaviour; their cognitive development can be slightly faster, and certain aspects of their intelligence are above the average. despite their disability, sma-affected people report high degree of satisfaction from life. palliative care in sma has been standardised in the consensus statement for standard of care in spinal muscular atrophy which has been recommended for standard adoption worldwide. prognosis in the absence of pharmacological treatment, people with sma tend to deteriorate over time. recently, survival has increased in severe sma patients with aggressive and proactive supportive respiratory and nutritional support. if left untreated, the majority of children diagnosed with sma type 0 and 1 do not reach the age of 4, recurrent respiratory problems being the primary cause of death. with proper care, milder sma type i cases (which account for approx. 10% of all sma1 cases) live into adulthood. long-term survival in sma type i is not sufficiently evidenced; however, as of 2007 advances in respiratory support seem to have brought down mortality. in untreated sma type ii, the course of the disease is slower to progress and life expectancy is less than the healthy population. death before the age of 20 is frequent, although many people with sma live to become parents and grandparents. sma type iii has normal or near-normal life expectancy if standards of care are followed. type iv, adult-onset sma usually means only mobility impairment and does not affect life expectancy. research directions since the underlying genetic cause of sma was identified in 1995, several therapeutic approaches have been proposed and investigated that primarily focus on increasing the availability of smn protein in motor neurons. the main research directions have been as follows: smn1 gene replacement gene therapy in sma aims at restoring the smn1 gene function through inserting specially crafted nucleotide sequence (a smn1 transgene) into the cell nucleus using a viral vector. this approach has been exploited by the first approved gene therapy for sma, scaav-9 based treatment onasemnogene abeparvovec. smn2 alternative splicing modulation this approach aims at modifying the alternative splicing of the smn2 gene to force it to code for higher percentage of full-length smn protein. sometimes it is also called gene conversion, because it attempts to convert the smn2 gene functionally into smn1 gene. it is the therapeutic mechanism of the approved medications nusinersen and risdiplam. branaplam is another smn2 splicing modulator that has reached the clinical stage of development. historically, this research direction investigated also other molecules. rg3039, also known as quinazoline495, was a proprietary quinazoline derivative developed by repligen and licensed to pfizer in march 2014 which was discontinued shortly after, having only completed phase i trials. ptk-sma1 was a proprietary small-molecule splicing modulator of the tetracyclines group developed by paratek pharmaceuticals and about to enter clinical development in 2013 which however never happened due to paratek downsizing at that time. rg7800, developed by hoffmann-la roche, was a molecule akin to risdiplam that has undergone phase i testing but was discontinued due to animal toxicity. early leads also included sodium orthovanadate and aclarubicin. morpholino-type antisense oligonucleotides, with the same cellular target as nusinersen, remain a subject of research in treating sma and other single-gene diseases, including at the university college london and at the university of oxford. smn2 gene activation this approach aims at increasing expression (activity) of the smn2 gene, thus increasing the amount of full-length smn protein available. oral salbutamol (albuterol), a popular asthma medicine, showed therapeutic potential in sma both in vitro and in three small-scale clinical trials involving patients with sma types 2 and 3, besides offering respiratory benefits. a few compounds initially showed promise but failed to demonstrate efficacy in clinical trials. butyrates (sodium butyrate and sodium phenylbutyrate) held some promise in in vitro studies but a clinical trial in symptomatic people did not confirm their efficacy. another clinical trial in pre-symptomatic types 1–2 infants was completed in 2015 but no results have been published. valproic acid (vpa) was used in sma on an experimental basis in the 1990s and 2000s because in vitro research suggested its moderate effectiveness. however, it demonstrated no efficacy in achievable concentrations when subjected to a large clinical trial. it has also been proposed that it may be effective in a subset of people with sma but its action may be suppressed by fatty acid translocase in others. others argue it may actually aggravate sma symptoms. it is currently not used due to the risk of severe side effects related to long-term use. a 2019 meta-analysis suggested that vpa may offer benefits, even without improving functional score. hydroxycarbamide (hydroxyurea) was shown effective in mouse models and subsequently commercially researched by novo nordisk, denmark, but demonstrated no effect on people with sma in subsequent clinical trials. compounds which increased smn2 activity