Genetic Imprinting Flashcards
What is genetic imprinting?
Genetic Imprinting is causally due to modification of a gene as it is transmitted through the father or the mother. These maternal or paternal “imprints” are erased, and re-established based upon the sex of the offspring
Describe the composition of teratomas and molar pregnancies and how this confirms the existence of genetic imprinting in humans.
Presence of both maternal pronuclei in the same germ cell results in ovarian teratomas or dermoid tumors, results in UNIPARENTAL DIPLOIDY; (ALL CHROMOSOMES ARE DERIVED FROM A SINGLE PARENT).
What is a hydatidiform mole?
Hydatidiform mole occurs when the chromosomes in the fertilized egg are only, or primarily, paternal in origin. The result is abnormal trophoblastic proliferation, and since no, or a decreased proportion of, maternal genes are present, little to no embryonic development occurs.
How does a complete mole occur?
A single sperm fertilizes an empty oocyte, and the sperm derived genome duplicates; Only paternal chromosomes present.
How does a partial mole occur?
A haploid ovum is fertilized, with subsequent duplication of the paternal haploid chromosomes, or via dispermy fertilization of an ovum.
Descibe genetic imprinting through generations.
Methylation pattern changes from generation to generation. The imprinting pattern of an individual is established prior to fertilization, and remains established during life. The imprints are erased in germ cells during gametogenesis, and new patterns are reestablished for the next generation prior to fertilization .
Describe the etiology of Prader-Willi syndrome
Deletions in Chromosome 15q11 inherited from the father.
Describe the symptoms of Prader-Willi syndrome
hypotonia, voracious apetite after age 2, cant regurgitate.
Describe the etiology of Angelman syndrome.
Deletions in Chromosome 15q11 inherited from the mother.
Describe the symptoms of Angelman syndrome.
Progressive microcephaly, happy puppet syndrome, seizures.
Describe uniparental disomy
Deletions in Chromosome 15q11 inherited from the mother (maternally inherited allele) results in Angelman Syndrome
Describe Beckwith-Weidemann Syndrome.
Macrosomia, Visceromegaly; can arise sporadically, inherited or alterations in the 11p15 region.
Describe the clinical risks of Beckwith-Weidemann syndrome.
High risk for embryonal tumors and neonatal hypoglycemia.
Describe the etiology of Russell Silver Syndrome.
Hypomethylation of paternal chromosome 11p15.5 is identified in 35%-50% of individuals with RSS, which results in decreased expression of IGF2 relative to normals.
Describe the clinical risks of Russell Silver Syndrome
Learning disability, neonatal hypoglycemia; No risk for tumors.
