Lecture 36 How do mutations affect health and crainofacial development? Flashcards
how many mutations is the average child born with that were not present in parents?
100-200
How many infants are born with a diagnosable genetic condition that can be attributed to a single major mutation?
- 1 in 50
What are some examples of chromosome disorders?
- aneuploidy
- rearrangements/translocations
- deletions
- insertions
- duplications
What is aneuploidy?
- an abberation in chromosome number caused by segregation of chromosomes during mitosis or meiosis
how many infants are born with aneuploidy?
- 1 in 400
Where do most cases of aneuploidy originate in?
- female meiosis I and risk rises with maternal age
Examples of aneuploidy
- 9p trisomy
- down syndrome
- edwards syndrome
key characteristics of down syndrome?
- upslanting palpebral fissure
- low set small folded ears
- short neck
- flattened nasal bridge
- brushfield spots
- epicanthal fold
What is the most common chromosomal condition?
- down syndrome
What is down syndrome?
- full or partial extra copy of chromosome 21
- 1 in 700 babies in the US
(6000 babies a year)
Most of the down syndrome cases can be classified as?
- nondisjunction (95% of cases)
What is the least common form of down syndrome?
- Mosaicism (1%)
What form of down snydrome is classified as a full or partial copy of chromosome 21 attaching to another chromosome (usually chromosome 14)
- Translocation (4%)
What is the main risk factor that has been linked to having a baby with down syndrome?
- Maternal age
results from nondisjunction or mosaicism
T/F most of the children with down syndrome come from mothers over the age of 35?
- False
- due to higher birth rates in younger women 80% of children with down syndrome are born to women under 35 years of age
What percentage of cases of down syndrome are traced to the father?
- 5%
Is heredity a factor in trisomy 21 (nondisjunction) and mosaicism?
- no
non craniofacial features of individuals with down syndrome
- low muscle tone
- small stature
- cognitive delay (very mild to severe)
- transverse palmar crease
(these traits vary)
What is a transverse palmar crease?
- a single deep crease across the center of the palm
How many adults with down syndrome reach age 60?
- 80%
What is the main thing to be concerned about with down syndrome patients?
- heart defects
- spinal problems
(always ask about heart problems)
What percent of children with down syndrome are born with some type of congenital heart defect?
- 50%
Spinal problems in down syndrome patients
- some people with down syndrome may have a misalignment of the top tow vertebrae in the neck
What is atlantoaxial instablility?
- misalignment of the top two vertebrae in the neck
- this condition puts them at risk of serious injury to the spinal cord from over extension of the neck (need extra support in chair)
Other considerations for treatment of down syndrome individuals?
- GI defects
- immune disorders
- sleep apnea
- obesity
- leukemia
- demential
- other problems
How should you describe a child with down syndrome?
- A child with down syndrome NOT (a downs child)
Is down syndrome a disease?
- no it is a condition or syndrome
Do people suffer from down syndrome?
- no they have it
- they are not afflicted by it
What word should you use instead of retardation?
- cognitive disability or intellectual disability
Is saying Downs appropriate?
- no
- an apostrophe denotes ownership
What are chromosomal rearrangements caused by?
- chromosome breakage or by recombination between mispaired chromosomes during meiosis
what chromosomal rearrangements are likely to cause disease?
- rearrangements that change the copy number of genes or that break up an important gene
How many infants are born with a symptomatic chromosomal rerrangement?
- 1 in 1000
Why is cri du chat chat called “cats cry”
- infants with this condition often have a high-pitched cry that sounds like that of a cat
What are some features of cri du chat syndrome?
- intellectual disability and delayed development
- small head size (microcephaly)
- Low birth weight
- weak muscle tone (hypotonia)
- transverse palmar crease
- some have heart defects
Cranial facial features of cri du chat?
- widely set eyes (hypertelorism)
- Low set ears
- small jaw (micrognathia)
- rounded face (moon facies)
- epicanthal folds
- broad nasal bridge
- downward- slanting palpebral fissures
What chromosome is associated with cri du chat?
- chromosome 5
Can cri du chat be inherited from unaffected parent?
- yes
- 10 % of cases
Do females or males have cri du chat more commonly?
- females
- 4:3 ratio
Symptoms of cri du chat
- cognitive disfunction
- facial defects
- small head
- low birth weight
How is cri du chat diagnoses?
- genetic testing
What is a dominant single gene disorder?
- expressed in heterozygotes who carry a single copy of the mutation
- severe dominant diseases are often caused by new mutation
What is a recessive single gene disorder?
- expressed only in homozygotes who have the mutation in both copies of the gene
Single gene disorders aka
mendelian disorders
Multifactorial diseases aka
polygenic diseases or complex diseases
What are multifactorial diseases caused by?
- caused not by a single major mutation but by interacting genetic and environmental risk factors
What is the most common diease?
- multifactorial
from allergies to diabetes and coronary heart disease, are multifactorial
What week is the growth phase of palatogenesis?
- week 7
What happens in the growth phase of palatogenesis?
- median palatal process (derived from medial nasal processes and frontonasal process) forms the primary palate
When is the elevation phase of palatogenesis?
- week 8
What happens in the elevation phase?
- nasal septum- derived from the frontonasal prominence
- palatal shelves- derived from the maxillary process of the first pharyngeal arch
When is the fusion phase of palatogensis?
- 9 weeks
- fusion forms secondary palate
What does the secondary palate do?
- separates the nasal cavity from the oral cavity
-
what is the secondary palate needed for?
- swallowing
- taste
- vomiting
- breathing
- speech
Cleft palate is the result of:
- failed palatogenesis
- (failure in PS growth)
- (failure PS elevation)
- (failure in PS fusion)
What is one of the most common birth defects in humans?
- cleft palate
Is the etiology of cleft palate only the same as that of cleft lip with cleft palate?
- no they are different
Cleft palate only
- is a specific defect in palatogenesis (weeks 7-10)
Cleft palate in Cleft lip/cleft palate
- is a secondary defect for a failed lip fusion (weeks 4-7)
- mom might know shes pregnant
How many cases are syndromic cleft palate?
- 30% of cases (cleft palate a phenotype of a know syndrome)
How many cases are non-syndromic cleft palate?
- 70% of cases (not associated with a know syndrome)
What are environmental causes of cleft palate?
- alcohol, phenytoin, retinoic acid, radiation, TCDD
What are nutritional/metabolic causes of cleft palate?
- low methionine, low folic acid, maternal DM, hypervit A
Genetic causes of cleft palate
- 350 + mendelian disorders. chromosomal aberrations?
Is the pathogenesis of clef palate fully understood?
- nope
Does current prenatal screening detect cleft palate?
- no
- screening occurs after it has happened
What is a problem caused by therapy in cleft palate patients?
- defective maxillary growth (due to scarring)
