Survival of motor neuron 1 (''SMN1''), also known as component of gems 1 or ''GEMIN1'', is a gene that encodes the
SMN protein in humans.
Gene
''SMN1'' is the
telomeric
A telomere (; ) is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes. Although there are different architectures, telomeres, in a broad sense, are a widespread genetic feature mos ...
copy of the gene encoding the SMN protein; the
centromeric
The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers ...
copy is termed ''
SMN2
Survival of motor neuron 2 (''SMN2'') is a gene that encodes the SMN protein (full and truncated) in humans.
Gene
The ''SMN2'' gene is part of a 500 kb inverted duplication on chromosome 5q13. This duplicated region contains at least four ge ...
''. ''SMN1'' and ''SMN2'' are part of a 500
kbp inverted duplication on chromosome 5q13. This duplicated region contains at least four genes and
repetitive element
Repeated sequences (also known as repetitive elements, repeating units or repeats) are short or long patterns of nucleic acids (DNA or RNA) that occur in multiple copies throughout the genome
In the fields of molecular biology and geneti ...
s which make it prone to rearrangements and deletions. The repetitiveness and complexity of the sequence have also caused difficulty in determining the organization of this genomic region. ''SMN1'' and ''SMN2'' are nearly identical and encode the same protein.
The critical sequence difference between the two is a single nucleotide in exon 7 which is thought to be an
exon splice enhancer
In molecular biology, an exonic splicing enhancer (ESE) is a DNA sequence motif consisting of 6 bases within an exon that directs, or enhances, accurate splicing of heterogeneous nuclear RNA ( hnRNA) or pre-mRNA into messenger RNA (mRNA). Introd ...
. It is thought that
gene conversion
Gene conversion is the process by which one DNA sequence replaces a homologous sequence such that the sequences become identical after the conversion event. Gene conversion can be either allelic, meaning that one allele of the same gene replaces a ...
events may involve the two genes, leading to varying copy numbers of each gene.
Clinical significance
Mutations in ''SMN1'' are associated with
spinal muscular atrophy
Spinal muscular atrophy (SMA) is a rare neuromuscular disorder that results in the loss of motor neurons and progressive muscle wasting. It is usually diagnosed in infancy or early childhood and if left untreated it is the most common genetic ...
. Mutations in ''SMN2'' alone do not lead to disease, although mutations in both ''SMN1'' and ''SMN2'' result in
embryonic death
Embryo loss (also known as embryo death or embryo resorption) is the death of an embryo at any stage of its development which in humans, is between the second through eighth week after fertilization. Failed development of an embryo often results i ...
.
References
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External links
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{{Chaperones
Spinal muscular atrophy