MCP 5

Question 1

Traits of Prader willi

Answer 1

small, hypotonic at birth, begin to gain weight because they overeat. small hands, small feet, hypogonadisum and bad temper, developmentally delayed and most to well in special education or group homes

Question 2

Traits of Angelman

Answer 2

severely MR, cannot carry on usually conversations but friendly, bursts of inappropriate laughter, hyperacitivty, short stature, microcephaly, seizures, ataxia (happy puppet symdrome)

Question 3

Causes of Prader willi

Answer 3

1. paternal deletion
2. maternal disomy (uniparental disomy)
3. maternal imprinting pattern (inherited from father) -> functionally maternal chromosomes although one from mom one from dad

Question 4

Causes of Angelman

Answer 4

1. maternal deletion
2. paternal disomy
3. paternal imprinting pattern (one from mom one from dad but maternal chromosome has paternal imprinting pattern–> functionally paternal chromosomes)

Question 5

Uniparental disomy

Answer 5

inheritance of a chromosome or chromosomes from 1 parent to the exclusion of the other
-cannot be detected by karyotype analysis must use molecular probe and even then we cannot tell if they are the same copy isodisomy or heterodisomic

Question 6

Uniparental isodisomy

Answer 6

• usually a result of meiotic nondisjunction –> monosomy
• zygote rescue duplicated the lone chromosme leading to the 2 copies of one
• mechanism has been identified in some CF patients

Question 7

Uniparental heterodisomy

Answer 7

• usually a result of meiotic nondisjunction–> trisomy
• zygote rescue randomly inactivates one chromosome (or deletes one) –> 2/3 of the time the desirable biparental heterodisomy is achieved but 1/3 of the time it leads to two different copies from one parent

Question 8

Imprinting

Answer 8

the differential modification of the maternal and paternal genetic contributions to the zygote resulting in the differential expression of parental alleles during development and in the adult
there are male and female differences
-lasts one generation
-change usually occurs at meiosis

Question 9

Methylation

Answer 9

• addition of methyl groups to cytosine residues in the DNA–> essentially turns genes off because there is no transcription (blocks binding of other cofactors and activators)
• can occur within a single gene or a group of adjacent genes
• can occur over a portion of a single chromosome
• can occur over the full length of one or more chromosomes
• the pattern of methylation can be different between males and females

Question 10

PWS and AS genes pattern of disfunction

Answer 10

• three genes SNRPN, necdin and UBE3A
• maternal pattern turns off SNRPN and necidin
• paternal pattern turns off UBE3A
• so patient needs copies of 2 chromosomes with appropriate imprinting pattern to have all genes expressed

Question 11

Are all chromosomes imprinted?

Answer 11

no

• 14 and 15 are
• large number of developmental genes are imprinted important for development of early zygote -> type of mutation is not usually associated with a change in DNA sequence but rather expression

Question 12

Epigentics

Answer 12

• the study of heritable changes in gene function that are NOT caused by a change in the DNA sequence
• modification of transcription that alters gene expression and thus phenotype
• this is a normal process required for “normal” cell function
• change in epigenetic effects can result in up or down regulation of genes and this can result in disease

Question 13

What are the primary categories of epigenetic modifications?

Answer 13

• histone modification
• chromatin remodeling
• DNA methylation

Question 14

Transcription factors

Answer 14

• bind to DNA and alter gene transcription
• act as an activator or repressor
• bind specifically to enhancer or promoter regions of the DNA adjacent to a specific gene

Question 15

MicroRNA (miRNA)

Answer 15

• small non coding RNAs
• miRNA bind to mRNA to regulate gene expression-> this can prevent translation or interfere with the translation process
• down regulation of miRNA caused by hypermethylation at miRNA promoters is reported in a number of tumors
• provide therapy targets and drug development

Question 16

Rett Syndrome

Answer 16

• predominantly in girls
• normal development followed by arrested development
• disruptions in motor function problems with control of hands and feet
• loss of speech, seizures, intellectual disability
• MECP2 -a transcription factor that can activate or repress transcription - normal function required for maturation of neurons and subsequent normal development
• phenotype variable - linked to X inactivation