Single Gene Disorders Flashcards
are AD dz alleles common or rare? are AD trait alleles common or rare?
dz alleles: rare
trait alleles: common
are AR dz alleles common or rare? are AR trait alleles common or rare?
AR dz alleles are common
AR trait alleles are rare
chromosome abn are seen in how many live births and are the leading cause of what?
1 in 150 live births
leadings cause of mental retardation and PG loss
what is aneuploidy?
deviation from the euploid (cell that has multiple of 23 chromosomes) by chromosome gain or loss
what is euploid?
cell that has a multiple of 23 chromosomes
gametes have how many chromosomes and are considered what?
23 chromosomes and are considered haploid
how many chromosomes do somatic cells have? they are considered what?
46
they are considered diploid
what is the MC autosomal trisomy?
trisomy 21 - down’s syndrome
RFs for trisomy 21? increased risk of what cancer w/this dx other effects?
increased w/increased maternal age
40% have congenital heart defects
increased risk of ALL
reduced fertility
MC causes of mental retardation?
down syndrome
fragile x syndrome
fetal alcohol syndrome
physical characteristics of down syndrome?
flattened nose and face upward slanting and eyes single palmar crease short 5th finger that curves inward widely separated first and second toes and increased skin creases on the feet
prognosis of edward syndrome? other name? malformations seen where? heart problems?
very poor prognosis, most trisomy 18
most don’t live past birth
AVSD, PDA
physical characteristics of edward syndrome?
hand and foot malformations low set ears and micrognathia occiput or back of skull is prominent, dysplastic or malformed ears, clenched hands with overlapping fingers flexed big toe, prominent heels small mouth, jaw, short neck shield chest short or prominent sternum wide-set nipples
what is patau syndrome? physical characteristics? prognosis?
trisomy 13 polydactyly cleft lip, palate microphthalmia (small eyes) microcephaly cardiac and renal defects very poor prognosis
are babies with autosomal monosomies going to have a good or poor outcome?
poor - most are inconsistent with a live birth
what is the only monosomy consistent with life? why is it the only one?
turner syndrome 45, X (also 46, XX, 47, XXX)
only one because it’s not autosomal
physical characteristics of turner syndrome?
marked short stature, ovarian dysgenesis and neurocognitive problems
can help pts with turner syndrome greater height by injecting with what?
growth hormone
what is 47, XXY known as?
klinefelter’s syndrome
XXY males are likely to have what health problems?
health issues which normally present in women such as breast cancer, thromboembolic disease and osteoporosis
at what stage in replication does klinefelter’s develop?
meiosis I
what does ‘hypogonadism’ in klinefelter’s refer to?
low levels of testicular atrophy with low levels of testosterone and elevated LH:FSH
effects of klinefelter’s syndrome?
appears over time, not at birth
XXY males have weaker muscles and reduced strength, as they grow older they tend to become taller than average
as teens may have larger breasts, weaker bones, lower E levels than peers
fertility of men with klinefelter’s?
reduced
47, XYY occurs in what stage of cell division?
anaphase II of meiosis II
nondisjunction leaves sperm cell with an extra copy of the Y chromosome
when do all women’s egg cells form? what stage are they left in then?
form during fetal development
remain in suspended meiosis prophase I until ovulation
when is nondisjunction more likely to occur?
during oogenesis (over spermatogenesis) also more likely to occur with increasing maternal age
probability of having a baby with down’s syndrome in women less than 30 yo? at age 35? at age 40?
1/1000 when less than 30
1/400 at age 35
1/100 at age 40
70% of down syndrome cases are identified by what?
triple screen (alpha-fetoprotein, chorionic gonadotropin and unconjugated estriol) +/- inhibin A
what is the quad test?
used to screen for down syndrome
includes: alpha-fetoprotein, HCG, estriol and inhibin A
done btw 15-20 wks of PG
what happens in a reciprocal translocation?
two non-homologous chromosomes break and exchange fragments
reciprocal translocations can cause what?
partial trisomies and partial monosomies
what is the philadelphia chromosome? it is an example of what?
philadelphia chromosome results from translocation of the long arms of chromosomes 9 and 22
reciprocal translocation after birth that affects oncogenes/tumor suppressor genes = cancer can grow more easily
if philadelphia chromosome happens in hematopoietic cells what can it result in?
CML
t (9,22) chromosome translocation causes what?
chronic myelogenous leukemia
t (15, 17) chromosome translocation causes what?
acute myelogenous leukemia
t (14, 18) chromosome translocation causes what?
follicular lymphoma
t (8, 14) chromosome translocation causes what?
burkitt’s lymphoma
t (11, 14) chromosome translocation causes what?
mantle cell lymphoma
what is a robertsonian translocation?
where both the short arms are lost
what happens in down syndrome translocation?
long arms of 14 and 21 pair
short arms disappear
3 chromosomes remain
what is the chromosomal abn in cri-du-chat?
deletion in 46, XX or 46, XY of 5p (deletion of short arm of chromosome 5)
what deletion is prader-willi syndrome? what deletion is angelman syndrome?
PWS: when there is a microdeletion on dad’s chromosome 15 transmitted to the child
AS: when there is a microdeletion on mom’s chromosome 15 transmitted to the child
how does prader-willi present? physical cahracteristics?
child has intense craving for food and will do almost anything to get it
can lead to weight gain and morbid obesity
trouble eating as an infant with poor weight gain
delayed motor development
narrow bifrontal skull
rapid weight gain
short stature
slow mental development
very small hands and feet in comparison
often small and floppy infants
male infants may have undescended testicles
how does angelman syndrome present? physical characteristics?
very happy children!
developmental delays such as lack of crawling or babbling at 6-12 mos and intellectual disability
lack of or minimal speech
inability to walk, move or balance well (ataxia)
trembling movement of arms and legs
frequent smiling and laughing
seizures that begin btw 2-3 yo
stiff or jerky movements
small head size with flatness in the back of the head
strabismus
tongue thrusting
walking with arms up in the air
light pigmentation of the skin, hair and eyes
what is inversion?
when chromosome segment btw 2 breaks is reinserted in the same location but in reverse order
still retain all of their genetic material so usu unaffected
are inversion carriers usu affected?
no because they retain all of their genetic material
what can a ring chromosome form from?
when a deletion occurs on both tips of a chromosome and remaining chromosome ends fuse together
how does an isochromosome form?
when a chromosome divides along the axis perpendicular to its normal axis of division
two copies of one but no copy of the other chromosome
are people w/isochromosomes affected?
yes b/c missing a whole chromosome unless involving the X chromosome then possibility to be non-fatal
