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GeneticDisorders-III

lecture 27 wilson

QuestionAnswer
multifactorial inheritance determined by 2 or more genes, conditioned by non-genetic influences; examples: cleft lip or palate, congenital heart dz, CAD, HTN, gout, DM, pyloric stenosis
advantages of FISH over cytogenetics able to detect submicroscopic aberrations, can use non-dividing (in interphase) cells for analysis
Down syndrome trisomy 21, most common constitutional chr abnormality, 1/700 births, associated with advanced maternal age
physical features of Down syndrom prominent epicanthal folds, low-set ears, macroglossia, MR, abundant neck skin, duodenal atresia ("double bubble"), congenital heart defects, HYPOtonicity, predisposition to leukemia
del(22q11.2) or DiGeorge/velocardiofacial syndrome microdeletion syndrome causing nasal-sounding speech, congenital heart defects, hypocalcemia and T-cell immunodeficiency b/c 4th pharyngeal pouch is absent = thymic and parathyroid a/hypoplasia
trisomy 18 (Edwards syndrome) lethal trisomy, 1/8000 births, clenched fists/HYPERtonicity can be seen on son, clinodactyly, intrauterine growth defects, congenital heart problems
trisomy 13 (Patau syndrome) lethal trisomy, midline defects = cleft lip and palate, holoprosencephaly, fusion of frontal lobes, agenesis of cerebellar vermis
term for inactivation of one X chr lyonization
heteropyknosis of one X chr results in? Barr body, occurs after 16th day of life
higher # of X chr can be associated with greater likelihood of phenotypic effect and MR XXY, XXXY
Turner syndrome 45XO, 1/2-3,000 births; phenotype: short stature, coarctation of aorta, webbed neck, streak ovaries = menopause before menarche, widely-spaced nipples. usually short females without mental compromise
Klinefelter syndrome XXY or XXXY, 1/500 births, more common than Down syndrome, phenotype: hypogonadism, pear-shaped figure due to overproduction of androgens that are converted peripherally to estrogen, long legs, infertility, no MR
genetic sex determined by presence/absence of sex-determining region of the Y chr (SRY gene)
gonadal sex histological appearance of gonads
ductal sex presence of Mullerian or Wolffian ducts
genital or phenotypic sex appearance of external genitalia
true hemaphrodite have both ovarian and testicular tissue, XX- or XY- cell lines
female hemaphrodite XX with ovaries but male external genitalia b/c they weren't able to respond to estrogens in utero. CAH - defect in enzyme resulting in overproduction of androgens
male hemaphrodite Y chr and testes but external genitalia are ambiguous or overtly female, results from androgen insensitivity, AR is defective so not able to respond even to nl levels of testosterone/DHT
Fragile X syndrome X-linked disorder, 200 or more CGG repeats in noncoding region of FMR-1 gene; phenotype: long face and mandible, large and everted ears, macro-orchidism, 2nd most common cause of MR
inheritance pattern of fragile X syndrome X-linked with differences; female carriers show manifestation usually, worsens with each generation (Sherman paradox) so grandfather was prob not affected, mother was mildly, grandson has full blown dz
example of trinucleotide repeat disorder affects coding region - Huntington dz
mitochondrial disorder COMPLETE maternal transmission; organs that use oxidative phosphorylation are affected, heteroplasmy, threshold effect. ex: Leber hereditary optic neuropathy
heteroplasmy tissues or entire organism harbor both mutant and WT-mitochondrial DNA
Prader-Willi disorder of genomic imprinting & microdeletion syndrome; mother has imprinted (silenced by methylation) chr 15 so when dad passes down chr 15 with microdeletion in that region + mom's silenced chr 15, dz develops
Angelman syndrome disorder of genomic imprinting & microdeletion syndrome; father has imprinted (silenced by methylation) chr 15 so when mom passes down chr 15 with microdeletion in that region + dad's silenced chr 15, dz develops
indications for prenatal genetic testing advanced maternal age, parent has chr aberration, prev child with one, sono-detected abnormalities, parent is carrier of an X-linked disorder
indications for postnatal genetic testing multiple congenital anomalies, MR/developmental delay, suspected autosomal numerical or structural or sex chr aberration, suspected fragile X, infertility, multiple spontaneous ab or FMHx of miscarriages
Created by: sirprakes on 2011-10-02



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