7 Dysmorphology

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  1. What are some reasons to consult a clinical geneticist?
    • • abnormal prenatal testing
    • • infant has 1 or more birth defects, an unusual appearance, or an abnormal genetic test result (eg. chromosome testing, newborn metabolic screening)
    • • child or adult with an unusual appearance, intellectual disability, or hx of birth defects
    • • family hx of birth defect(s) or inherited conditions
    • • infertility, recurrent miscarriages
    • • early onset cancer/strong family hx of cancer
  2. Why make a genetic diagnosis?
    • • defines the abnormalities present (what should & shouldn’t be expected)
    • • provides a prognosis for the future (eg. can provide a range for life expectancy)
    • • explains why the condition occurred
    • • allows for genetic counseling of all family members (re: recurrence risk)
  3. Birth Defect
    a condition present at birth which requires medical, surgical or cosmetic intervention

    • diagnosed in 3% of children at birth

    • by 1 year of life, 4% of children will have some type of birth defect diagnosed

    • eg. congenital heart disease, neural tube defect, polydactyly
  4. What percent of babies will have no minor malformations?

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    shows that as the number of minor malformations increases, the likelihood of having a major malformation in conjunction greatly increases
  5. Dysmorphic Features
    • variants of physical features that exist in a small percent of the general population

    • 3 OR MORE dysmorphic features/minor anomalies correlate with a possible genetic syndrome

    • occur more commonly in genetic syndromes

    • eg. single transverse palmar crease

    ~ when you don’t look like the rest of the family
  6. How many dysmorphic features strongly correlate with a possible genetic syndrome?
  7. What percent of diagnosis are based on a lab test?
  8. Things to review in Family Hx:
    • • developmental delay
    • • birth defects
    • • birth defects
    • • genetic conditions
    • • ethnic background
    • • consanguinity
  9. Things to review Prenataly:
    • prior obstetric history

    • patient’s pregnancy (eg. weight gain, illnesses, medications/drugs, fetal movement, prenatal diagnosis, twins, diabetes)
  10. Things to review Perinataly:
    • how labor & delivery went

    • hospital course

    • how the baby’s doing at home (how they’re feeding, sleeping, & what early milestones have been accomplished)
  11. Ear Positioning Variant
    • top 1/3 of the ear should about line up to the corner of the eye, rotated 20 degrees from vertical

    • B: low-set ears because if you draw line from eye, ear is below; also ears are angled more posteriorly than 20 degrees

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    - just a variation; the more of these a person has the more likely he/she is to have a syndrome
  12. Preauricular Pit
    • nodule, dent or dimple located anywhere adjacent to the external ear

    • majority of people do not have
  13. Orbital Hypertelorism
    • wide-set eyes

    • an abnormally increased distance between the eyes; the distance between the inner eye corners as well as the distance between the pupils is greater than normal
  14. Pectus Excavatum
    • sunken or funnel chest

    • a congenital chest wall deformity in which several ribs + the sternum grow abnormally, producing a concave, or caved-in appearance in the anterior chest wall
  15. Malformation
    morphologic defect resulting from an intrinsically abnormal developmental process

    • the program wasn't correct to start with, was never going to be right

    • present from the minute of conception

    • eg. cleft lip/palate, webbed digits

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  16. Deformation
    • an abnormal form or position of a part of the body caused by MECHANICAL, non-disruptive forces

    • started okay, but there was a pressure on the fetus such that it ended up being deformed

    • eg. foot binding, club feet (if fetus gets stuck in uterus in abnormal position, the force on foot → unable to develop in normal way)

    • has the potential to return to normal

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  17. What are two types of Deformations?
    1. congenital dislocation of the hip (happens during breached birth)

    2. clubfoot
  18. Disruption
    • a defect resulting from a breakdown of, or interference with, an originally normal developmental process

    • like deformation, but stops normal development in tissue

    • never going to return to normal
  19. What's an example of a Disruption?
    Amniotic Band Syndrome resulting in amputation of a finger

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  20. Dysplasia
    • abnormal cellular organization or function within a specific tissue type throughout the body → clinically obvious structural changes

    • eg. hemangioma or skeletal dysplasia such as osteogenesis imperfecta
  21. Problems in Morphogenesis
    • poor formation of tissue → Malformation (cleft lip/palate)

    • unusual forces on normal tissue → Deformation; can potentially be fixed (club feet)

    • breakdown of normal tissue → Disruption; permanent damage (amniotic band syndrome)

    • abnormal organization of cells in tissues → Dysplasia (hemangioma)

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  22. What are the different originating factors of a syndrome, sequence, & association?
    • Syndrome: due to a genetic factor

    • Sequence: due to a mechanical factor

    • Association: due to an unknown factor
  23. Syndrome
    pattern of multiple anomalies thought to be pathogenically related

    eg. Down Syndrome, trisomy 21; Progeria (or Neurofibromatosis type 1)
  24. Association
    a pattern of anomalies that occur together frequently, without a known, underlying cause
  25. C.H.A.R.G.E
    • used to be an Association, now it's a Syndrome caused by truncating mutations identified in CHD7 in 2/3 of patients (a helicase binding protein)

    • • C: colobomas (hole) of the eye
    • • H: heart defects
    • • A: atresia choanae (nAsal passage blockage)
    • • R: retarded growth & development
    • • G: genital hypoplasia
    • • E: ear anomalies including hearing loss
  26. Sequence
    a pattern of multiple anomalies derived from a single known or presumed mechanical factor or prior anomaly

    • Pierre Robin: tongue falls back & obstructs airway

    • Potter: not enough amniotic fluid
  27. Pierre Robin Sequence
    in utero, the chin is very small & the tongue prevents closure of the soft (cleft) palate

    after birth, the small chin results in the tongue falling back & obstructing the airway
  28. Potter Sequence
    in utero, lack of fetal urination (2ndary to absent/non-functional kidneys or blockage of urine outlet) leads to the absence of amniotic fluid (anhydramnios)

    this results in fetal compression & pulmonary hypoplasia → neonatal death

    * SEQUENCE because it's caused by a mechanical factor
  29. What are some of the etiologies of Intellectual Disability (6)?
    • 1. multiple congenital malformations
    • 2. metabolic
    • 3. isolated intellectual disability
    • 4. cerebral palsy/siezures
    • 5. CNS lesions
    • 6. Environmental
  30. Teratogens
    • • substances encountered during pregnancy that can cause birth defects
    • • effect on the fetus is highly dependent on the gestational age at time of exposure & dose
    • • Infectious (rubella, syphilis, CMV)
    • • Medications (thalidomide, accutane, antiepileptics)
    • • Drugs of abuse (cocaine, alcohol)
    • • External agents (radiation, hyperthermia)
    • • Maternal Disorders (diabetes, lupus, PKU)
  31. Teratogen as a Morphogenic Problem
    • can be classified as a Disruption

    • can CAUSE malformations
  32. FAS (Fetal Alcohol Syndrome)
    • • short palpebral fissures
    • • flat midface
    • • short nose
    • • indistinct philtrum (lines between lip & nose)
    • • minor ear anomalies
    • • low nasal bridge
    • • epicanthal folds

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  33. Causes of Birth Defects
    • 43.2% Unknown
    • 23% Multifactorial
    • 10% Chromosomal Abnormalities
    • 3% Single Gene Defect
    • 3% Prenatal Teratogen Exposure
    • 2.5% Uterine
    • 0.4% Twinning
Card Set:
7 Dysmorphology
2016-08-27 14:36:35
MedFoundationsI Genetics Exam1
Genetics Exam 1
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