Lect 1: Intro to Medical Genetics Flashcards
patterns of inheritance can be
dominant vs. recessive
autosomal vs. X-linked
inherited vs. acquired dz
inherited gene complement
-mutations may be transmitted from one or both parents
acquired gene complement
a subset of cells in an individual that arose by clonal propagation from a single mutation in one cell
inborn errors of metabolism
genetically determined biochemical disorder in which a specific enzyme produces a metabolic block
What are two mechanisms by which a specific enzyme produces a metabolic block
- accumulation of substrate which could be toxic
2. deficiency of products
alcaptonuria
accumulation of homogenistic acids in the blood; damage to cartilage, heart and kidney
–dark urine
ALBINISM
can be complete meaning that there is no pigment in any organ or tissue or it can be partial.
Enzyme Defect
If a mutation is present and a substrate cannot be converted to a normal product secondary pathways
may show an increase in activity
The substrate cannot be converted to product 1 or 2, but rather than have a buildup of that substrate, other enzymes activate to convert the substrate to other things (S2, S3, S4)….so that you avoid toxic buildup of substances in the cell.
Deficiency of a Shared Enzyme
a single mutation can affect multiple cellular processes
What are some general clinical features of pts with biochemical disorders
poor growth
mental retardation
problems in general metabolism
neurological problems
- Hyperphenalaninemias are a group of disorders related to the function of phenylalanine hydroxylase (PAH) which converts phenylalanine to tyrosine.
They include
phenylketonuria (PKU)
variant PKU
defects in tetrahydrobiopterin
Phenylketonuria
due to defect in PAH causing phenylalnine to accumulate in the cells
it is linked to
mental retardation
PHE accumulates and when it does so in nervous tissue cells it damages them causing MR
mom has to be put on a special diet that is low in PHE
If she comes off of it and introduces back into her life, PHE can cross the placenta, damaging the fetus (even tho the baby is not affected with PKU)
Variant PKU and Non-PKU hyperphenylalaninemia
Non-PKU is less damaging and may not require the diet
Another cause of hyperphenylaninemia
is due to mutations along the pathway that make tetrahydrobiopterin (BH4).
-due to locus heterogeneity, mutations in different genes involved in BH4
To make PHE from Tyr you need PAH. PAH requires BH4.
If BH4 is has a metabolism defect it can lead to PHE accumulation
The problem is that BH4 is a cofactor or other enzymes and its absence in other pathways leads to
a deficit in neurotransmitters such as dopamine and serotonin
How do you treat this?
Since PAH is normal, you only need to give 1. oral BH4
2. To normalize neutrotransmitters int he brain, patients require supplementation with the products of the disrupted step such as L-dopa or Trp-OG
What are lysosomal storage dz?
They are caused by mutation of a lysosomal storage enzyme that leads to failure of degradation and the accumulation of macromolecules in lysosomes
include Tay-Sachs
- GM2 Gangliosidoses
3 dzs due to defect in the pathway
Tay Sachs is due to
a deficiency of hexosiminidase A (hex A) which results in the inability to degrade GM2 gangliosides so they accumulate, especially in the brain.
How do children with Tay-Sachs appear?
they appear normal at birth but hten they begin to decline.
what is a dead giveaway for Tay Sachs
cherry red spot in the retina of the eye….children become progressively worse, losing control of their extremities and usually die btw ages 2 and 4
- Mucopolysaccharidoses
is due to the absence of enzyme involved in degradation of glycosaminoglycans. if the enzyme is absent or defective the chain will not be degraded.
