Embryo Ch. 20

Front 1

What is a malformation?

Back 1

a morphologic defect that results from an intrinsically abnormal developmental process; thought to be error in morphogenetic/ developmental field (i.e. chromosome abnormality)

Front 2

What is a disruption?

Back 2

results from the extrinsic breakdown of, or an interference with, an originally normal developmental process; not inherited (i.e. teratogen- drug or virus)

Front 3

What is deformation?

Back 3

an abnormal shape or part that results from mechanical forces (i.e. intrauterine compression due to oligohydramnios- causes club foot due to low amounts of amniotic fluid)

Front 4

Spina bifida cystica is an example of...

Back 4

deformation- meningomyelocele produces intrinsic functional disturbances that may lead to fetal deformation

Front 5

What is dysplasia?

Back 5

abnormal organization of cells into tissues (dyshistogenesis- abnormal tissue formation); often nonspecific, affecting several organs (i.e. ectodermal dysplasia)

Front 6

What is a polytopic field defect?

Back 6

pattern of anomalies derived from a single developmental field

Front 7

What is a sequence?

Back 7

pattern of multiple anomalies derived from a single known structural defect/mechanical factor

Front 8

What is a syndrome?

Back 8

pattern of multiple anomalies thought to be pathogenetically related and not known to represent a single sequence or a polytopic field defect (i.e. trisomy 21)

Front 9

What is an association?

Back 9

a nonrandom occurrence in two or more individuals of multiple anomalies not known to be a polytopic field defect, sequence, or syndrome (statistically related defects)

Front 10

What is the inactivation of the X gene?

Back 10

in autosomal cells (of a female), one X chromosome is inactivated and turned into sex chromatin, while the other remains activated; this occurs during implantation.

important because carriers of an X-linked disease have the mutant gene causing the disease- may see discordance in monozygotic twins if one twin has the paternal X activated and the other has the maternal X activated

Front 11

Which X in Turner Syndrome is missing?

Back 11

paternal X in 75% of the cases

Front 12

What is mosaicism?

Back 12

when two or more cell types contain different numbers of chromosomes (some normal, some abnormal)-> leads to a milder phenotype and IQ may be normal

Front 13

How many masses of sex chromatin are present in Klinefelter syndrome?

Back 13

XXY= 1 mass of sex chromatin (males usually don't have sex chromatin)

Front 14

What causes mosaicism?

Back 14

nondisjunction & anaphase lagging (normal chromosome separation but delayed migration- chromosome lost as a result)

Front 15

What is a hygroma (lymphangioma) and in what disease is it seen in?

Back 15

excessive accumulation of watery fluid (hydrops) in the posterior head and cervical region, causes the loose neck skin and webbing seen in Turner syndrome

Front 16

What are the phenotypic characteristics of Edward's syndrome (trisomy 18)?

Back 16

MR, growth retardation, ventricular septal defect, clenched fists with characteristic positioning of the fingers (second and fifth ones overlapping the third and fourth), short sternum, narrow pelvis

Front 17

What are the phenotypic characteristics of Patau's syndrome (trisomy 13)?

Back 17

MR & other CNS deformations, bilateral cleft lip, low-set malformed ear, polydactyly (extra digits), microophthalmia

Front 18

What are 2 causes of triploidy?

Back 18

failure of the polar body to separate from the oocyte during meiosis II or dispermy

Front 19

What is a "blighted embryo?"

Back 19

when a tetraploid embryo aborts very early and all that is recovered is an empty chorionic sac (usually occurs during the first cleavage division)

Front 20

What is cri du chat syndrome? What is the characteristic phenotype?

Back 20

a partial terminal deletion from the short arm of chromosome 5

phenotype: weak catlike cry, microencephaly, MR, congenital heart disease, hypertelorism (space between orbits)

Front 21

What is a contiguous gene syndrome? What are two examples? What are the characteristic phenotypes of each?

Back 21

abnormality of 2 or more genes located next to each other on a chromosome

Prader- Willi syndrome- del 15q12, paternal chromosome is lost and only maternal chrom. is expressed-- short stature, mild MR, obesity, hyperphagia (overeating), hypogonadism

Angelman syndrome- del 15q12, maternal chrom. is lost and only paternal chrom. is expressed-- severe MR, microcephaly, brachycephaly (shortness of head), seizures, ataxic (jerky) movements of limbs and trunks

Front 22

What is paracentric vs. pericentric inversion?

Back 22

paracentric inversion- single arm of a chromosome

pericentric- inversion involves both arms and includes the centromere (carriers- offspring may have unequal crossing over and malsegregation at meiosis)

Front 23

What is the most common structural abnormality of the X chromosome? What is it? In what syndrome is this normally seen?

Back 23

isochromosome- centromere divides transversely instead of longitudinally- one arm is missing and the other is duplicated- have short stature and other stigmata of Turner's

Front 24

What is acondroplasia?

Back 24

a dominantly inherited congenital anomaly that results from a G-to-A transition mutation at nucleotide 1138 of the cDNA in the FGF receptor 3 gene on 4p

phenotype: short stature, short limbs & fingers, normal length of trunk, bowed legs, relatively large head, depressed nasal bridge

Front 25

What is Fragile X syndrome?

Back 25

most commonly inherited cause of moderate MR, found in males, fragil
e X chromosome at Xq27.3 or an expansion of CGG nucleotides in a certain region of the FMRI gene

Front 26

What causes uniparental disomy? What is it seen in?

Back 26

trisomic conceptus, followed by loss of extra chromosome in an early postzygotic cell division--> "rescued cell" = both chromosomes derived from 1 parent

Front 27

What are homeobox genes?

Back 27

found in all vertebrates; highly conserved sequences involved in early embryonic development and specify identity and spatial arrangements of body segments

Front 28

What is sonic hedgehog (Shh)?

Back 28

a secreted protein that sets off a chain of events in target cells, activates and represses target cells by transcription factors in the Gli family (Shh-Ptch-Gli pathways)

Front 29

Where is Shh expressed?

Back 29

notochord, floorplate of the neural tube, brain, polarizing activity of the developing limbs, the gut

Front 30

What is holoprosencephaly?

Back 30

mutations in the HPE 3 gene (Shh); midline defect of CNS septation, facial clefting, single central incisor, hypotelorism, or a single cyclopic eye

--> Shh converted to active form by cholesterol moiety, shares traits with Smith-Lemli-Opitz syndrome (brain & limb abnormalities)

Front 31

What disorders show mutations in the Gli 3 gene?

Back 31

(autosomal dominant)-- Greig cephalo-polysyndactyly syndrome (deletions or point mutations); Pallister-Hall syndrome with hypothalamic hamartomas, central or postaxial polydactyly