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19 Cards in this Set
- Front
- Back
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indications for chromosome analysis
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1. 2 or more major malformations
2. 1 major malformation in the presence of mild anomalies 3. specific chromosome syndrome syspected 4. MR and/or dysmorphic features 5. ambiguous or abnml genitalis 6.female w.short stature 7. offspring of a parent w/ a balanced translocation 8. parents of an offspring with a balanced translocation 9.recurrent abnormalities or infertility |
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down syndrome
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-mental retardation
-almond shaped eye -palmar crease -epicanthic fold -congenital heart defects -GERD -results from non-disjunction -trisomy, translocation, mosaicism (2 diff cell lines) |
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maternal age effect seen in down syndrome
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-occurs with a freq of 1/2000 live births b/t 18-24
-1/300 between ages 25-35 -1/100 at age 40 |
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Edward syndrome- trisomy 18
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-1/6000 live births
-rocker-bottom feet -tightly clenched fists -malformations of heart, kidney and digestive systems -mental retardation -10% live beyond 1st yr |
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Triploidy
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-rare
-seen in approx 20% of spontaneous abortions -karyotype has 69 chromosomes -results primarily from dispermy (2 sperms fertilizing 1 egg) -preg: polyhydramnios, hemorrhaging, pre-eclampsia -low set ears, adrenal, heart, kidney abnormalities |
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marker chromosome
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-a marker chromosome (mar) is an unidentifiable structurally abnormal chromosome
ex. 46,X +mar |
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ring chromosome
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-usually formed by a break in the long arm and a short arm of a chromosome
-the ends attach and form a circle ex. 46, X, r (X) |
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XYY males
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-phenotypically nml
-tall than avg -paternal meiotic nondisjunction -fertile and nml intellectually |
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XX males
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-arises by exchange outside the pseudoautosomal region of the X and Y at meiosis
-phenotype is similar to Klinefelter, however, the XX males are shorter than avg males and have nml intelligence -the testis determining factor on the Y (SRY) is translocated to the X -this results in an XX male or XY female |
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Fragile X syndrome
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-most common cause of inherited mental retardation in the pop
-males: large ears, long face, macroorchidism, speech impairment, abnml behavior, 15% autistic -females: mental impairment in 1/3 of cases, mild learning disabilities |
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fragile X syndrome cont.
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-first assoc with a fragil site on the long arm of the X chromosome
-Induction of the Fragile X chromosome was achieved by growth of cells in low folate medium -fragile X gene discovered in 1991 -It is associated with an expansion of the CGG sequence in the 5’ untranslated region of the gene in affected individuals |
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fragile X gene (FMRI)
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-Repeated trinucleotide CGG sequence
-Expansion of this repeat is responsible for the Fragile X syndrome 6-50 repeats: Normal 50-200repeats: Carrier >200 repeats: Affected -diagnose using southern blot and PCR |
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Fragile X syndrome: inheritance
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-nonpenetrant males transmit the fragile X gene to 50% of his daughters
-females carrying the fragile X gene are unaffected in this generation -carrier females transmit the fragile X gene to 50% of their offspring -expression of the syndrome is dependant on the # of repeats inherited (200) |
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genomic imprinting
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-the sex of the transmitting parent determines the phenotype of the offspring
-ex. fragile x syndrome |
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Cri Du Chat
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-results from a deletion of part of the short arm of chromosome %
-high pitched cry of infants -microcephaly, moon-shaped face, microangatia -Severe mental retardation, hypotonia, diverse malformations of the heart, kidney and abdomen |
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Prader-Willie syndrome
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-the deleted chromosome is always on the paternal chromosome
-genomic imprinting |
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Angelman syndrome
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-deletion of the maternal chromosome 15
-"Happy Puppet" -severe postnatal growth retardation, severe mental retardation and absence of language -prominent chin, fair hair, constant dribbling |
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DiGeorge sydrome
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-microdeletion of chromosome 22
-aplasia or hypoplasia of the thymus and parathyroid glands -conotruncal cardiovascular anomalies -die within 1st month of life |
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Velocardiofacial syndrome
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-microdeletion of chromosome 22 in 90% of cases
-prominent forehead -deep-set eyes -straight nose -slender hands |
