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17 Cards in this Set

  • Front
  • Back
Autosomal Dominant Inheritance
1. Only one copy necessary for expression
2. Transmission is vertical
3. Equal number affected males and females
4. Male to male transmission
5. Unaffected individuals have unaffected children; ie. If you didn’t inherit the gene then you wont pass it on!
6. Disorder may arise as a new mutation
Achondroplasia
1. AD inheritance
2. Most common form of short-limbed dwarfism (1 per 10,000 live births)
2. Over 90% of cases are new mutations
3. Gene was localized to 4p16 in 1994
4. Causative gene is FGFR3
5. Molecularly and clinically homogeneous
6. All affected individuals have a substitution for glycine at aa #380 of protein
Clinical Characteristics of Autosomal Dominant Disorders
1. Variable Expressivity
2. Penetrance
3. Advanced Paternal Age
Advanced Paternal Age
increases risk for new (de novo) mutations (“hot spots” in the genome)
Penetrance
(the proportion of people who carry the gene who present with any of the known phenotypic effects of the gene)
-Penetrant: you carry the gene and express the trait
-Non-penetrant: you carry the gene but show no clinical expression
Variable expressivity
family members may express to different degrees
Autosomal New Mutation
CHARGE
Autosomal Recessive Inheritance
1. Two copies needed for expression
2. Both parents are carriers, generally clinically normal
3. Family history often negative? What does this mean..phenotypically
4. Equal number affected males and females
5. Consanguinity may be present
6. May see ethnic predisposition
Example of ARI
Diastrophic Dysplasia
Diastrophic Dysplasia
1. Autosomal recessive condition
2. Distinct skeletal dysplasia characterized by disproportionate short stature, club foot, cleft palate, “hitchhiker’s thumb”, and “cauliflower ear”
3. Results from mutation in the diastrophic dysplasia sulfate transporter gene, DTDST
4. More common in individuals of Finnish ancestry
5. Associated with normal intelligence and postnatal development
X-Linked Recessive Disorders
- Hemizygous males affected
- Heterozygous females unaffected
- Incidence is much higher in males than females
- No male to male transmission
- Carrier females may show variable expression due to lyonization
Possible Explanations for seeing X-Linked Recessive Disorders in Females
1. Cells with normal X are inactivated in disproportionate numbers (lyon hypotheseis)
2. Affected female has 45,X karyotype
3. X chromosome rearrangement with deletion of normal gene, and inactivation of normal X
4. Affected female has an affected father and a carrier mother (rare)
5. Disorder is genetically heterogenous (really AR)
X-Linked Dominant Inheritance
1. More females affected than males
2. Sometimes lethal in males
3. Affected males will have no affected sons, but ALL daughters will be affected
4. Affected females have 50% chance of passing gene on with each pregnancy
X-linked dominant disorders are less common than X-linked recessive disorders
Example of X-Linked Dominant
Vitamin D Resistant Rickets
X-linked Dominant Incontinentia Pigmenti: Lethal in males
Mitochondrial Inheritance
1. MITOCHONDRIA HAVE THEIR OWN DNA!!!!
2. 16.5kb circular dsDNA containing 37 genes
3. 2 rRNAs, 22 tRNAs, 13 ox. phos. subunits
4. Most ox phos subunits are encoded by nuclear DNA: autosomal recessive
only mitochondria from oocyte contribute to zygote
5. MATERNAL INHERITANCE
DNA description of mito DNA
- 16.5kb circular dsDNA
- has 37 genes
Mutation in Diastrophic Dysplasia
diastrophic dysplasia sulfate transporter gene
-DTDST