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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]
Only 12 known human families are described in scientific literature to have SMA-PME. [2] SMA-PME is associated with a missense mutation (c.125C→T) or deletion in exon 2 of the ASAH1 gene and is inherited in an autosomal recessive manner. [3] SMA-PME is closely related to a lysosomal disorder disease called Farber lipogranulomatosis. [4]
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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 ]
Thus, allele R is dominant over allele r, and allele r is recessive to allele R. [4] Dominance is not inherent to an allele or its traits . It is a strictly relative effect between two alleles of a given gene of any function; one allele can be dominant over a second allele of the same gene, recessive to a third, and co-dominant with a fourth.
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.
Distal hereditary motor neuronopathies (distal HMN, dHMN), sometimes also called distal hereditary motor neuropathies, are a genetically and clinically heterogeneous group of motor neuron diseases that result from genetic mutations in various genes and are characterized by degeneration and loss of motor neuron cells in the anterior horn of the spinal cord and subsequent muscle atrophy.