Genetics q-bank Flashcards
Mode of inheritance in achondroplasia?
Autosomal dominant IRL 75% of patients are de novo mutations
Mode of inheritance in Marfans?
Autosomal dominant
What is the classical x-ray finding in achondroplasia?
Rhizomelic shortening of the limbs Trident hands Normal length trunk ie: proximal bone shortening of femur and humerus with normal distal limbs
What gene is involved in achondroplasia?
FGFR3
How do you diagnose achondroplasia?
Clinically! Only sequence the gene if in doubt or atypical case
Name the most common and most serious complications in achondroplasia
lumbosacral spinal stenosis is the most common other common: delayed motor milestones, otitis media, bowing of the lower legs, GERD, sweating, snoring, lumbar lordosis serious: hydrocephalus, craniocervical junction compression, restrictive pulmonary disease, upper airway obstruction, thoracolumbar kyphosis
Can achondroplasia be diagnosed antenatally?
Yes, there can be limb foreshortening on ultrasound but before counselling a parent confirm with molecular testing of the FGFR3 gene as the bone findings are non-specific
What should every infant with achondroplasia be evaluated for?
Unexpected infant death secondary to central apnea from compression of the arteries at the level of the foramen magnum: CT or MRI, polysomnography, careful neurologic histories and physical exams always put infant in a seat or carrier that supports their neck and back, minising uncontrolled head movement
What is the most common fatty acid oxygenation disorder?
MCAD Medium Chain AcylCoA Dehydrogenase Deficiency (autosomal recessive)
What is the typical presentation of MCAD?
Episodes of acute illness triggered by prolonged fasting: hypoketotic hypoglycemia with no or minimal metabolic acidosis -hepatomegaly with fat deposition, transaminitis and synthetic defects, including build-up of ammonia
What is the prognosis of MCAD?
Excellent if they avoid prolonged fasting and hypoglycemia; no cognitive impairment or cardiomyopathy. Fasting tolerance increases with age, some have muscle pain and reduced exercise tolerance. SCREEN SIBLINGS since as many as 35% of affected patients never have an episode
What are common organic acidemias and how do they present?
Maple syrup urine disease Methylmalonic acidemia Propionic acidemia Isovaleric acidemia (sweaty feet) They present with metabolic acidosis + ketosis, neutropenia, hyperammonemia with CEREBRAL EDEMA Stop catabolism, don’t give leucine/isoleucine/valine, patient may require dialysis. TEST urine organic acids (aka organic acidURIAs = urine)
How does MSUD present?
within first few days of life with hypoglycemia, ketones, metabolic acidosis and hyperammonemia correction of blood glucose does not correct the condition!
How do urea cycle defects present? Which is the most common?
Hyperammonemia and respiratory alkalosis after a high protein diet or catabolic state. Ornithine Transcarbamylase Deficiency is the most common
What tests to perform on T21 at birth?
confirmatory karyotype CBC, TSH Echo cataract & hearing screens
What tests to perform on T21 at 6 months, 12 months and then annually?
CBC, TSH ophtho hearing
When do you do cervical spine x-rays in a T21 patient?
At 3-5 years or when participating in contact sports OR if symptomatic
When do you do a celiac screen in a T21 patient?
At 2 years or if they are symptomatic!
When do you do a sleep study in a T21 patient?
By 4 years old
What are the classic findings of galactosemia?
Eyes (cataracts) Liver (substrate buildup and direct bili *jaundice) Kidneys (RTA) Brain (mental retardation) **increased risk of E. coli sepsis screen for with urine reducing substances confirm with GALT
How to diagnose galactosemia?
The demonstration of nearly complete absence of galactose-1-phosphate uridyl transferase (GALT) activity red blood cells (RBCs) is the gold standard for diagnosis
What is the treatment for galactosemia?
Soy formula
How to diagnose Klinefelters?
Karyotype: XXY
What’s particular about puberty in Klinefelters?
Puberty occurs at the normal age, but the testes remain small. Patients develop secondary sex characters late; 50% develop gynecomastia. Tall stature.
What to do with a positive PKU screen?
diagnosis should be confirmed by quantitative measurement of plasma phenylalanine concentration
Findings of a patient with PKU?
mousy odor normal at birth, vomiting develops profound mental retardation/seizures/spasticity/hyperreflexia/tremors
What is the breakdown of T21 etiologies and why do we care?
95% classic SPORADIC T21 (1% recurrence) 4% Robertsonian (translocation 21-21 100% recurrence, otherwise variable 5-7%) 1% Mosaicism
What two features characterize Schwachman-Diamond?
exocrine pancreatic insufficiency cytopenias also short & small(<3rd% x2), skeletal & dental abnormalities
What are characteristics of fetal hydantoin syndrome?
Limb: small, absent nails, hypoplastic distal phalanges, altered palmar creases, digital thumb, dislocated hip Craniofacial: hypertelorism, wide fontanelle, broad nasal bridge, low hair line, coarse scalp hair, broad alveolar ridge, short neck, metopic ridging, microcephaly, cleft lip & palate, abnormal ears, epicanthal folds, ptosis, coloboma About 10% of infants will have a major malformation, 30% have minor abnormalities.
What is the mode of inheritance in PKU?
autosomal recessive
What is osteopetrosis?
RARE autosomal recessive disorder in the acidification required for osteoclast function presents with macrocephaly, HSM, deafness, blindness, severe anemia, FTT, delay. Commonly have fractures, osteomyelitis, dental problems x-rays with bone-within-bone appearance
What are clinical features of Fragile X?
macrocephaly macroorchidism long and narrow face with prominent forehead and chin (prognathism), large ears joint hyperlaxity MVP
What is Waardenburg Syndrome?
Syndrome with depigmented areas of skin and hair deafness occurs in 9-37% of heterochromia irides +/- Hirschsprung in type IV
What’s the metabolic cocktail?
In suspected inborn errors of metabolism, mega doses of cofactors can be started and have been found to be effective for a number of disorders: Cobalamin (B12) Thiamine (B1) Biotin Riboflavin Folic Acid Carnitine
What is the classic cardiac finding in Turner’s?
Left ventricular outflow tract abnormalities: Bicuspid aortic valve Aortic stenosis Coarctation of the aorta MVP