Small supernumerary marker chromosome
Encyclopedia
Humans typically have 22 pairs of autosomal chromosome
s in our cells
, and a pair of sex chromosomes. About 2.7 million individuals have an extra, 47th autosomal chromosome called a small supernumerary marker chromosome (sSMC). These small supernumerary marker chromosomes can originate from any of the 24 different human chromosomes. About 70% of the cases with sSMC are de novo (new mutation
s), 30% are inherited within a family.
About 30% of the carriers of a sSMC are clinically abnormal. The main problem in connection with a sSMC appears when the diagnosis of the presence of a sSMC is made prenatally. Until recently there was no possibility to make clear predictions about the outcome of the pregnancy. However, research is being carried out into the link between the presence of a sSMC in individuals and any consequent symptoms.
Chromosome
A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...
s in our cells
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....
, and a pair of sex chromosomes. About 2.7 million individuals have an extra, 47th autosomal chromosome called a small supernumerary marker chromosome (sSMC). These small supernumerary marker chromosomes can originate from any of the 24 different human chromosomes. About 70% of the cases with sSMC are de novo (new mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
s), 30% are inherited within a family.
About 30% of the carriers of a sSMC are clinically abnormal. The main problem in connection with a sSMC appears when the diagnosis of the presence of a sSMC is made prenatally. Until recently there was no possibility to make clear predictions about the outcome of the pregnancy. However, research is being carried out into the link between the presence of a sSMC in individuals and any consequent symptoms.