5q<unk>  is a single disease that manifests over a wide range of severity, affecting infants through adults. Before its genetics was understood, its varying manifestations were thought to be different diseases – Werdnig–Hoffmann disease when young children were affected and Kugelberg–Welander disease for late-onset cases. In 1990, it was realised that these separate diseases formed a spectrum of the same disorder.<unk>  was then classified into 3–5 clinical types based either on the age of symptom onset or on the maximum motor function achieved. Currently, the consensus is that the phenotype of<unk>  spans a continuum of symptoms without clear delineation of subtypes. However, the traditional classification, outlined in the table below, is still used today both in clinical research and sometimes, controversially, as a criterion of access to therapies. Type Eponym Usual age of onset Natural history (without pharmacological treatment) OMIM<unk>  0 Prenatal Symptoms are observed at birth and often become apparent in the prenatal period as reduced foetal movement. Affected children typically have only a single copy of the SMN2 gene and usually survive only a few weeks even with 24/7 respiratory support. This form is very rare – accounts for approx. 2% of cases.<unk>  1(Infantile) Werdnig–Hoffmann disease 0–6 months This form is diagnosed in around 50% of patients, in whom the disease manifests in the first few weeks or months of life.<unk>  then has a quick and unexpected onset, with various muscle groups failing progressively. Infants never learn to sit unsupported and most gradually lose most of their muscle function. Death is usually caused by the failure of the respiratory muscles induced by pneumonia (frequently, aspiration pneumonia). Unless offered respiratory support and/or pharmacological treatment early, babies diagnosed with<unk>  type 1 do not generally survive past two years of age. With proper respiratory support, those with milder<unk>  type 1 phenotypes, which account for around 10% of<unk>  1 cases, are known to survive into adolescence and adulthood even without pharmacological treatment, although they always require round-the-clock care.<unk>  2(Intermediate) Dubowitz disease 6–18 months The intermediate form, diagnosed in around 20% of patients, denotes people who were able to maintain a sitting position at least some time in their life but never learned to walk unsupported. The onset of weakness is usually noticed some time between 6 and 18 months of life. The progress is known to vary greatly, some people gradually grow weaker over time while others through careful maintenance remain relatively stable. Body muscles are weakened, and the respiratory system is a major concern as are muscle contractures and spinal curvature. Life expectancy is reduced, even as most people with<unk>  2 live well into adulthood even without treatment.<unk>  3(Juvenile) Kugelberg–Welander disease >12 months The juvenile form, diagnosed in around 30% of patients, manifests after 12 months of age, or after the children have already learned to make at least a few independent steps. The disease progresses slowly, and most people with<unk>  3 lose walking ability sometime in their lives, requiring mobility support. Respiratory involvement is rare and life expectancy is normal or near-normal.<unk>  4(Adult onset) Adulthood This denotes the adult-onset form, sometimes also classified as a late-onset<unk>  type 3. It occurs in approx. 5% of patients and usually manifests in the third or fourth decade of life. The symptoms consist of gradual weakening of leg muscles, which frequently makes it necessary for the patient to use walking aids. Other complications are rare and life expectancy is unaffected. For convenience, care-focused publications classify patients into "non-sitters", "sitters" and "walkers" based on their actual functional status. Motor development and disease progression in people with<unk>  is usually assessed using validated functional scales – CHOP-INTEND (The Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders) or HINE (Hammersmith Infant Neurological Examination) in infants; and either the MFM (Motor Function Measure) or one of several variants of the HFMS (Hammersmith Functional Motor Scale) in older patients. The eponymous label Werdnig–Hoffmann disease (sometimes misspelled with a single n) refers to the earliest clinical descriptions of childhood<unk>  by Johann Hoffmann and Guido Werdnig. The eponymous term Kugelberg–Welander disease named after Erik Klas Hendrik Kugelberg (1913–1983) and Lisa Welander (1909–2001), who first documented the late-onset form and distinguished it from<unk>  dystrophy. Very rarely used Dubowitz disease (not to be confused with Dubowitz syndrome) is named after Victor Dubowitz, an English neurologist who authored several studies on the intermediate<unk>  phenotype.
Spinal muscular atrophy
Prader–Willi syndrome
Spinal and bulbar muscular atrophy
Duchenne muscular dystrophy
Madras motor neuron disease
Congenital muscular dystrophy
Muscular dystrophy
Distal spinal muscular atrophy type 1