NBME Answers : furkan7's page

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submitted by trazabone(16), visit this page

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My understanding is that if parents are unrelated by blood to those affected, we assume that they are not carriers (in the recessive case). Therefore, if we have a male father affected with x-linked recessive married to a non-carrier, there's no way any of his offspring would be affected.

"If one parent is not a carrier, then a child can only inherit a disease allele from the other parent. In these problems, we can assume that any individual marrying into the family is not a carrier." https://www.cs.cmu.edu/~genetics/units/instructions/instructions-CP.pdf

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linwanrun1357 If we assume that they are not carriers (in the recessive case) Then how came it can be AR？！！ +3

catscan1979 ^exactly what's said above here. I think x-linked recessive is the least likely, but not impossible. +4

furkan7 How is x linked recessive is the least likely when we need 2 carrier females for compatibility of both autosomal recessive and X linked recessive inheritence to this pedigree? I think probability of these two are the same. Am I missing something? +1

submitted by lsmarshall(465), visit this page

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"Parasternal heave (lift) occurs during right ventricular hypertrophy (i.e. enlargement) or very rarely severe left atrial enlargement." RV hypertrophy can be seen so easily because the RV is at the anterior surface of the chest.

In this patient blood from LA to LV decreases in saturation, so it is going somehwere. From the O2 sat. we can deduce there is probably a VSD (increased RV pressure would cause RVH and parasternal heave). Furthermor, the vignette is likely describing tetralogy of fallot (caused by anterosuperior displacement of the infundibular septum). In Tet spells, RV outflow is too obstructed and patient gets cyanosis and R>L shunting Squats increase SVR, decreasing R>L shunting, putting more blood through pulmonary circuit and relieving cyanosis.

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seagull i'm pretty sure your a prof and not a student. +30

nor16 nevertheless, we are greatful for explanation! +1

niboonsh I remember seeing a question describe parasternal lift in the context of pulm htn. still got this wrong tho fml +

anotherstudent Did my question have a typo? It says O2 saturation in the right ventricle is 70, which is equal to the Right atrium and vena cava. It says the O2 saturation in the left ventricle is 82%, which is a decrease from the LA (95) but not equal to the RV, which is why I thought there wasn't a VSD, I assumed there was a weird shunt from the LV to some other part. Will O2 saturation not always equalize? +1

pseudomonalisa This is a right to left VSD due to the pulmonic stenosis present in Tetralogy of Fallot. O2 sat will be low (70) in the right ventricle, and from there it'll enter the left ventricle and mix with freshly oxygenated blood coming from the left atrium (95). Because of the mixing, the O2 sat of blood in the left ventricle will be somewhere in the middle of 70 and 95 (82 in this case). You're correct, though, that most other VSDs are left to right and you'd see greater O2 sat in the right ventricle in that case (not sure if it equalizes with the left ventricle though). +1

furkan7 I does not need to equalizes.Moreover, in left to right shunt,left ventricle's O2 saturation is close to 100% +

an1 If the LV blood is going into the RV, why didn't it's O2 sat increase? neither did the pulmonary artery's. I agree it's TOF, but the sats really don't make sense for a VSD... +