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Genetic Medicine: Clinical Genetics and Inborn Errors of Metabolism - Part 2 (13 test)
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1. A standard karyotypic analysis is ordered for a girl with heart defects, developmental delay, and an unusual appearance. The results are normal, but a colleague suggests the diagnosis of DiGeorge-velocardiofacial spectrum and recommends a FISH test with results shown in the figure A control probe highlights the chromosomes 22s in the metaphase spread and the test probe gives a signal on one of the chromosomes 22. Which of the following statements best summarizes this result?
- The initial karyotype results are inconsistent with the FISH results.
- This is a normal result, making the diagnosis of DiGeorge-velocardiofacial syndrome less likely.
- A small deletion is present on one of the patient’s number 22 chromosomes, confirming the suspected diagnosis.
- The FISH test was not useful, since the initial karyotype results were normal.
- The chromosome with the positive signal is paternal in origin.
2. A female who is at risk to be a carrier of hemophilia A desires prenatal She does not want her extended family to know about her pregnancy if the fetus is affected. Which of the following prenatal diagnostic techniques should be advised?
- Amniocentesis with western blot analysis of factor VIII
- Chorionic villus sampling with DNA analysis for factor VIII mutations
- Percutaneous umbilical blood sampling with testing of factor VIII levels
- Amniocentesis with DNA analysis for factor VIII mutations
- Chorionic villus sampling with assay of factor VIII activity
3. A 4-year-old African American girl presents with Prader-Willi syndrome obesity, short stature, hypogonadism, and mental disability. Despite a normal gestation and delivery, she had extremely low tone (hypotonia) in the newborn nursery and had to be tube-fed until age 6 months. At age 3 years, she began eating too much, taking food from her parents’ plates and even foraging in the garbage for food. Her physician suspects the diagnosis of Prader-Willi syndrome, and recalls that about 60% of Prader-Willi patients have a small deletion on the proximal long arm of chromosome 15. Which of the following techniques would be most accurate in testing for this deletion?
- Standard karyotyping of peripheral blood leukocytes
- Northern blotting of mRNAs transcribed from the deletion region
- Restriction analysis to detect DNA fragments from the deletion region
- Rapid karyotyping of bone marrow
- Fluorescent in situ hybridization (FISH) analysis of peripheral blood lymphocytes using fluorescent DNA probes from the deleted region
4. A child is referred for evaluation because of low muscle tone and developmental delay. Shortly after delivery, the child was a poor feeder and had to be fed by tube. In the second year, the child began to eat voraciously and became He has a slightly unusual face with almond-shaped eyes and downturned corners of the mouth. The hands, feet, and penis are small, and the scrotum is poorly formed. The diagnostic category and laboratory test to be considered for this child are which of the following?
- Sequence, serum testosterone
- Single birth defect, serum testosterone
- Deformation, karyotype
- Syndrome, karyotype
- Disruption, karyotype
5. A 14-year-old Caucasian adolescent has mild disability requiring resource classes and is obese because the parents have had great difficulty controlling her food intake at school and in her grandmother’s house where she goes after school. Her physician decides to test for Prader-Willi syndrome and knows that the paternal imprint on chromosome 15 is absent in this condition as opposed to the maternal imprint in Angelman A fluorescent in situ hybridization (FISH) test for chromosome 15 deletion had been normal when developmental delay was first suspected, but the physician decides that the girl’s increased appetite may reflect uniparental disomy (two chromosome 15 from one parent) that has caused a milder form of Prader-Willi syndrome. Southern blotting is performed to determine the origin of the patient’s number 15 chromosomes. In the figure below, a hypothetical Southern blot with DNA probe D15S8 defines which of four restriction fragment length polymorphisms (RFLPs) are present in DNA from mother (M), child (C), and father (F). Which of the following accurately conveys the result of this test?
- Biparental origin of chromosome 15, confirming a diagnosis of Prader-Willi syndrome
- Origin of both chromosome 15 from father, suggesting a diagnosis of Angelman syndrome
- Origin of both chromosomes from the mother, suggesting a diagnosis of Prader-Willi syndrome
- Absence of a paternal chromosome 15, diagnosing nonpaternity and excluding a diagnosis of Prader-Willi syndrome
- Indeterminate result because the D15S8 locus is deleted in the child
6. The figure in Question 5 demonstrates that the child is missing both paternal chromosome 15 alleles; nonpaternity is a more plausible explanation than uniparental disomy. The hypothetical Southern blot shown below illustrates a DNA “fingerprinting” analysis to examine paternity, where maternal (M), child (C), and paternal (F) DNA samples have been restricted, blotted, and hybridized simultaneously to the probes D7Z5 and D20Z1. The distributions of restriction fragment alleles suggest which of the following?
- The child is adopted
- False maternity (ie, baby switched in the nursery)
- False paternity
- Correct maternity and paternity
- None of the above
7. An infant with severe muscle weakness is born to a mother with mild muscle weakness and myotonia (sustained muscle contractions manifested clinically by the inability to release a handshake). The mother’s father is even less affected, with some frontal baldness and cataracts. Worsening symptoms in affected individuals of successive generations suggest which of the following inheritance mechanisms?
- Genomic imprinting
- Unstable trinucleotide repeats
- Multifactorial inheritance
- Mitochondrial inheritance
8. Most isolated congenital anomalies exhibit which of the following?
- Mendelian inheritance
- Chromosomal inheritance
- Multifactorial inheritance
- Maternal inheritance
- Atypical inheritance
9. A newborn Caucasian girl has bilateral club feet (feet deviated inward and malformed) with minimal movement of her lower She has a midline bulge over her lower spine that by MRI shows absent vertebrae with extrusion of spinal cord tissue and surrounding dura as a subcutaneous cyst. The lesion is diagnosed as spina bifida occulta and is known to follow the usual multifactorial determination of spina bifida and other common birth defects. Spina bifida exhibits female predilection with an incidence of 1 in 1000 Caucasian individuals and recurrence risks of 3% for first-degree relatives and 0.5% for second-degree relatives. The risk can be decreased by two-thirds if mother takes folic acid before conception. What is the risk that the parent’s second child will have spina bifida if mother takes folic acid before becoming pregnant?
- 1 in 1000
- 3 in 1000
- 1 in 100
- 3 in 100
- Less than 0.1%
10. Neural tube defects, such as spina bifida and anencephaly, are best diagnosed by which of the following laboratory tests?
- Chorionic villus biopsy and karyotype at 10 weeks after the last menstrual period (LMP)
- Maternal serum α-fetoprotein (MSAFP) levels and ultrasound at 16 weeks after conception
- Amniotic fluid α-fetoprotein (AFP) levels and ultrasound at 16 weeks after the LMP
- Amniotic fluid acetylcholinesterase levels at 16 weeks after conception
- Amniotic fluid karyotype and ultrasound at 16 weeks after the LMP
11. A couple has a child who has been diagnosed with medium-chain acyl-coenzyme A (CoA) dehydrogenase deficiency (MCAD-MIM*201450), a condition that affects the body’s ability to metabolize medium-chain fatty This couple is now expecting another child. What is the risk that this child will have MCAD?
12. In the treatment of propionic acidemia, which of the following is contraindicated?
- A diet high in fatty acids
- Caloric supplementation
- Aggressive fluid and electrolyte management
13. Which of the following is most likely in an untreated child with PKU?
- Elevated tyrosine
- Increased skin pigmentation
- Decreased skin pigmentation
- Normal phenylalanine hydroxylase levels
- Elevated alanine