We often associate biochemistry with undergrad, but biochemistry is present in many specialties! Let’s dive into the types of biochem questions you may see!
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Biochemistry is more applicable to some specialties than others. But just basic genetics and metabolic diseases, for instance, are seen in many specialties. Biochemistry comes into play especially when you talk about metabolic diseases. Hence, it's a commonly tested subject on the exam, more than the other basic science components.
A healthy married couple has a child who develops clinical symptoms of what you suspect to be a rare disease. Genetic testing revealed the patient's mother carries the mutated gene, but the father is not a carrier. However, the father's brother had the same disease, which has also occurred in one of his sisters' sons.
This pattern is characteristic of which of the following diseases?
Note from Andrea: The question is drawing you a pedigree. You can jot down a little diagram of pedigree for yourself as you're going through it. You have to figure out the pattern from the pedigree but know which diseases of the options fit that pattern of inheritance.
Answer choices:
(A) G6PD
(B) Cystic fibrosis
(C) Phenylketonuria (PKU)
(D) Alpha-1 antitrypsin deficiency
(E) Tay-Sachs Disease
Once you've drawn that pedigree and determined what the inheritance pattern is, you can go through each option and cross out what doesn't fit or jot down what pattern each one has.
In this case, the couple is healthy and not showing any disease. But the one child does and the father is not a carrier. This gives you another hint. So if he's not a carrier, how is that possible if the child is showing the disease?
Then you're seeing that it's present in the father's brother and one of the sisters' sons. Here, you can see a distinctive pattern where this is not an autosomal recessive type pattern. This leads you to a dominant X-linked route.
As you draw this out, you will start to see the pattern where the children follow up to them. The mother is a carrier, the father is not. And the child has the disease. It's likely that the child is a male because they're receiving only an X from the mom. So this would be an X-linked pattern. Now, you would only see one that follows that X-linked disease – G6PD
Looking at patterns and pedigrees can really help you. Another algorithm Andrea found helpful is to ask: does the child with the disease have a parent with a disease. If no, then you're skipping a lot of things.
You're left here with X-linked recessive which is 50% more common than a male child. Therefore, it's an X-linked recessive disease.
Most students are using mnemonics to remember all of the X-linked recessive diseases. This is most common for autosomal recessive or autosomal dominant. There's no way to think through them in a way that doesn't require memorization. The names of the disease don't really help in this case. All this being said, Andrea recommends using mnemonics. You can also use visual mnemonics you can look at or silly drawings to help you remember stuff.
Probably, if the question talked about a food that this person that this person may develop symptoms with, then you could probably remove some answer choices out. For example, G6PD is one of those...