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Flashcards in SAQ Disease Deck (24)
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1

Human deafness + complementation

Many loci affect hearing pathway from outer ear to auditory nerve and brain
- Partial or total inability to hear, most commonly on both ears.
- Can be inherited by recessive genes (most common) , dominant genes + X-linked patterns
- 70% total registered cases are non syndromic, which means that there are no other signs or medical problems associated with the hearing loss.
- DFNA1 first gene mapped for non syndromic hearing loss
- Costa Rican family - single base change in the gene caused low frequency onset progressive hearing loss.
- Autosomal dominant inheritance pattern for that particular mutation.
- Penetrance age of 30.

2

Phenylketonuria, PKU

Mutations in the PAH gene result in low levels of the enzyme phenylalanine hydroxylase.
- Build up of dietary phenylalanine to potentially toxic levels.
- gene-environment interaction, chemical
recessive
- can’t break down Phe -> special diet
- Untreated PKU can lead to intellectual disability, seizures, behavioral problems and mental disorder.

3

Achondroplasia

- abnormal adult stature.
If both parents have the condition, a homozygous child is not likely to live.
- 80% of cases of dwarfism caused by achondroplasia.
- Autosomal dominant inheritance.

4

Cystic Fibrosis

- Disease affecting mainly the lungs, intestine, pancreas and kidneys.
- Failure in transmembrane conductance regulator (transport protein).
- Chloride ion transporter.
- Differences in amino acids account for the disfunction of the protein.
- Loss of phenylalanine in the sequence.
- Accumulation of mucus in respiratory and gastrointestinal tracts.
- Autosomal recessive. 1/25 allele incidence among populations of European ancestry.
- Prone to lung infections.
- No cure, only treatment for the symptoms.
- Males affected by the condition are infertile.
- Can be diagnosed by genetic screening.

5

Albinism

- Absence of pigment in hair/skin. Recessive Mendelian Inheritance - Autosomal recessive
- Congenital disorder characterised by the complete or partial absence of melanin in the hair, skin and eyes.
- TYR gene for tyrosinase deficient, an important enzyme in the melanin-producing pathway
- Pleiotropic effects include vision and hearing impairments.
- Deletions and duplication of the gene coding for the enzyme
- Causes susceptibility to skin cancer and chronic sunburns.

6

Autism

- Gene interaction and multiple loci involved
- Several genes affect one character (polygenic trait)
Autism Spectrum Disorders (ASD) are characterised by the autistic triad:
- Impaired social communications and interactions.
- Restricted and obsessive interests and behavior.
- Language impairment.
- Neurodevelopmental disorder
- 1 locus alters phenotype produced by other locus.

7

Lesch-Nyhan syndrome

- Characterised by the error in purine metabolism.
- Self-mutilation and death are common amongst affected individuals.
- Deficiency in hypoxanthine-guanine phosphoribosyltransferase.
- Gene located on the X chromosome (sex-linked)
- Buildup of uric acid in bodily fluids
- Neurological signs include poor muscle control and intellectual stability.
- Poor utilization of Vitamin B12

8

Duchenne muscular dystrophy

- Severe type of X-linked (recessive) inherited muscular atrophy + X-chromsome inactivation
- Muscle loss predominantly in the upper legs and pelvis, followed by muscle loss along the arms.
- Detect age 3-5, fatal in 20’s - Most individuals affected are unable to walk by the age of 12.
- Carrier females may show some symptoms.
- Mutation in the protein dystrophin -> Protein important in the maintaining of muscle fibre cell membranes.
Individual will have high intravenous creatine kinase.
-> MZ twins 1 had DMD, the other didn’t

9

Colourblindness

Daltonism; condition in which individual does not see a difference between certain colors (red-green being the most common manifestation).
- X-linked inherited condition
- More males affected than females. Males need only one copy (for their only X chromosome).
- Females would need to have a carrier mom and an affected father.
-> Heterozygous women can see in colour even though some retinal cells are colour blind due to x chromosome inactivation..
- Decreased visual acuity due to cone and rod dystrophy.
- Cones are color sensing cells in the retina, when impaired cannot distinguish certain colors accurately.

10

Patau syndrome

- Chromosomal abnormality in which all or some of the cells trisomy 13 may be due to translocation
- Extra genetic material disrupts normal development
- Causes multiple and complex organ defects.
- Predominantly caused by nondisjunction.
- More than 80% of children with this condition die during their first year of life.

11

Myeloid leukemia

Translocation 5-11/ 9-22 can be induced by chemical exposure and even radiation.
-> myeloid line of blood
- abnormal WBC in bone marrow or lack of creates susceptibility to infections

12

Cri-du-chat

Chromsome deletion -> loss of tip of chr. 5
- Vocal cord abnormalities attribute a kitten sound to individuals voices, hence the name.
- Individuals have small head and jaws, wide eyes and unusual facial features.
- Growth retardation is a common symptom.

13

Turner’s syndrome

XO, female
Aneuploidy

14

Edward’s syndrome

Trisomy 18, aneuploidy
- Symptoms include a short and webbed neck, low-set ears, low hairline, and swollen feet and hands at birth.
- Kidney + Heart defects, diabetes and low thyroid hormone levels common in the condition.
- Infertility and lack of breasts and menstrual periods.

15

Gynandromorphs

Half male half female - mosaic due to error in mitosis in early dip.
- Somatic aneuploidy
- Dm one red eye, one white

16

Porphyria variegata

Deficit in PPOX gene for protoporphyrinogen oxidas
can’t break down seventh heme -> porphyrin component of Hb so it accumulates (light sensitive chemical)
gene-environment interaction - low tolerance to bright light.
- Incomplete penetrance
- Neurological symptoms = light sensitivity, low doses of barbiturates = lethal
- vomiting, diarrhea, constipation, muscle weakness, seizures, increased anxiety and hallucinations.
- Autosomal dominant acute form of porphyria that primarily affects the skin.

17

VLINCL

Progressive encephalopathies in children with psycho-motor deteriaration, visual failure + premature death -> inbreeding
- Prevalent in Finnish Islands.
- Neurodegenerative disease resulting from an excessive accumulation of lipopigments in bodily tissues
- In neuronal cells as well as liver, spleen, myocardial, and kidney cells.
- Nonsense and frameshift mutations in the CLN1 gene.
- Lysosomal enzyme (palmitoyl protein thioesterase) deficiency.

18

Ragged red fibres

Progressive myoclonic epilepsy
- mitochondrial disease
- moters to sons/daughters

19

Retinoblastoma

In Tristan da Chunha - bottleneck effect -> 1 woman of initial 3 people had the allele
-> 2 somatic mutations OR 1 inherited mutations + 1 somatic.
- Rare form of cancer that rapidly develops from immature cells in the retina
- Most common type of malignant cancer in young children.
- Most common mutation in 13q14 -> Gene that codes for a tumor suppressor gene.
- Somatic amplification of the MYCN oncogene

20

Proteus syndrome

Overgrowth of bone, mutation, somatic, Joseph Merrick
Rare congenital disorder that causes skin overgrowth and atypical bone development.
- Abnormal tumor and cyst growth throughout the body also a characteristic of the disease
- Mutation in AKT1 kinase in a mosaic state gene.
- Other mutations in chromosomes 10 and 16 suggested to be causing the disease.

21

Bloom syndrome

Short stature, predisposition to dvp cancer, genomic instability. Mutation in DNA repair enzyme = recessive.
- Autosomal recessive disorder characterized by shortage in stature, predisposition of cancer development and genomic instability.
- Caused by mutations in the BLM gene leading to a mutated form of helicase.
- Cells exhibit a striking genomic instability that includes excessive crossovers between homologous chromosomes and sister chromatid exchanges.
- Strongly correlated with cancer and rapid aging

22

Werner syndrome

Mutation in DNA repair enzymes.
- Autosomal recessive progeroid syndrome characterized by premature aging
- WRN (gene in chromosome 8) protein deficiency causes changes in the pattern of gene expression.
- Decrease the stability of mRNA, which increases the rate at which it is degraded.
- Presence of bilateral cataracts, atrophied and tight skin, soft tissue calcification and sharp facial features are also key features of the condition.

23

Leber's HON

- Hereditary optic neuropathy.
- Mitochondrially inherited degeneration of ganglion cells and their axons that leads to an acute or subacute loss of central vision.
- Majority of mutations comprising this condition affect subunit genes of complex I of the oxidative phosphorylation chain in mitochondria.
-Men cannot pass the disease onto their offspring.

24

Tay-Sachs Disease

- Autosomal recessive disorder.
- Incomplete dominance.
- Characterized by the progressive deterioration of of nerve cells.
- Mental and physical abilities impaired.
- Usually results in early death about 4 years after birth.
- Deficiencies in hexosaminidase enzyme activity.
- Mutation in chromosome 15
- Cell death caused by ganglioside accumulation.
- No cure or treatment.
- Prevalence in Ashkenazi Jewish populations - negative assortative (non-random) matching influences the H-W balance