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Autosomal recessive proximal spinal muscular atrophy, responsible for 90-95% of cases and usually called simply spinal muscular atrophy (SMA) – a disorder associated with a genetic mutation on the SMN1 gene on chromosome 5q (locus 5q13), diagnosed predominantly in young children and in its most severe form being the most common genetic cause ...
Spinal muscular atrophy (SMA) is a rare neuromuscular disorder that results in the loss of motor neurons and progressive muscle wasting. [3] [4] [5] It is usually diagnosed in infancy or early childhood and if left untreated it is the most common genetic cause of infant death. [6]
XL-SMA is characterized by severe hypotonia and areflexia with loss of anterior horn cells in the spinal cord (i.e., lower motor neurons). [4] The disease course is similar to that in the most severe forms of classic autosomal recessive SMA caused by mutation of SMN1: SMA type 0 (SMA0) and SMA type I (SMA1). [ 4 ]
The terms autosomal dominant or autosomal recessive are used to describe gene variants on non-sex chromosomes and their associated traits, while variants on sex chromosomes (allosomes) are termed X-linked dominant, X-linked recessive or Y-linked; these have an inheritance and presentation pattern that depends on the sex of both the parent and ...
Spinal and bulbar muscular atrophy (SBMA), popularly known as Kennedy's disease, is a rare, adult-onset, X-linked recessive lower motor neuron disease caused by trinucleotide CAG repeat expansions in exon 1 of the androgen receptor (AR) gene, which results in both loss of AR function and toxic gain of function.
Normally, two recessive alleles need to be inherited (one from each parent) for the recessive trait to be expressed but recessive merely means that the trait is only expressed in the absence of the dominant alleles. The pattern of inheritance in which a single recessive allele is inherited but is still expressed is known as pseudodominance.
According to the model of Mendelian inheritance, alleles may be dominant or recessive, one allele is inherited from each parent, and only those who inherit a recessive allele from each parent exhibit the recessive phenotype. Offspring with either one or two copies of the dominant allele will display the dominant phenotype.
The disease has only been identified as distinct from SMA recently, so research is still experimental, taking place mostly in animal models. Several therapy pathways have been devised which include gene therapy , whereby an IGHMBP2 transgene is delivered to the cell using a viral vector , [ 7 ] and small-molecule drugs like growth factors (e.g ...