angelman syndrome
Nondisjunction is an error or failure of a pair of chromosomes to separate adequately during the process of cell division. Any cells that are not related to those cells of sexual reproduction such as blood cells, muscle cells, etc divided by mitosis. Nondisjunction literally means not coming apart, during a nondisjunction error the chromosomal segregation results in an uncharacteristic result of chromosomes.
There are two types of nondisjunction’s that can occur, Meiosis I and Meiosis II.
Any nondisjunction event that occurs during Meiosis I are extremely important due to the most clinical relevant aneuploidies in our human body result during this type of segregation error. During the first step of Meiosis I, bivalents assemble and hten follow homologous recombination.
During Meiosis II Ovulated eggs become halted in the second phase until fertilization helps trigger the division of the second meiotic. Very similar to the segregation events that occur in Mitosis, the sister chromatids consequentially separate in anaphase during meiosis II.
The syndrome that I chose to discuss is Angelman Syndrome, I never knew what Angelman’s was until the physicians at CHOP wanted to test my 9 month old for the choromosonal defect. My daughter at 9 months, was still not sitting up unassisted. She wasn’t making the typical baby noises and sounds that most babies make. She wasn’t reaching all of the milestones her peers her age were. She seemed to posses typical symptoms of Angelmans and we wanted to be sure that we ruled it out. Proximal markers showed reduction to homozygosity of paternal alleles, intermediate markers showed nonreduction, and distal markers reduction, thus suggesting a meiosis II nondisjunction event in the father with two crossovers. This is, to our knowledge, the first reported case of AS due to meiosis II nondisjunction. (http://www.ncbi.nlm.nih.gov/pubmed/10450868)
There are two types of nondisjunction’s that can occur, Meiosis I and Meiosis II.
Any nondisjunction event that occurs during Meiosis I are extremely important due to the most clinical relevant aneuploidies in our human body result during this type of segregation error. During the first step of Meiosis I, bivalents assemble and hten follow homologous recombination.
During Meiosis II Ovulated eggs become halted in the second phase until fertilization helps trigger the division of the second meiotic. Very similar to the segregation events that occur in Mitosis, the sister chromatids consequentially separate in anaphase during meiosis II.
The syndrome that I chose to discuss is Angelman Syndrome, I never knew what Angelman’s was until the physicians at CHOP wanted to test my 9 month old for the choromosonal defect. My daughter at 9 months, was still not sitting up unassisted. She wasn’t making the typical baby noises and sounds that most babies make. She wasn’t reaching all of the milestones her peers her age were. She seemed to posses typical symptoms of Angelmans and we wanted to be sure that we ruled it out. Proximal markers showed reduction to homozygosity of paternal alleles, intermediate markers showed nonreduction, and distal markers reduction, thus suggesting a meiosis II nondisjunction event in the father with two crossovers. This is, to our knowledge, the first reported case of AS due to meiosis II nondisjunction. (http://www.ncbi.nlm.nih.gov/pubmed/10450868)