QUESTION 89
A 5-year-old child is being seen by his pediatrician because his parents are concerned regarding his behavior during his first year of school. They are concerned that he has autism. Physical examination reveals large ears and large testicles. Of the following, what type of mutation or chromosomal abnormality underlines this child’s condition?
A. Point mutation
B. Frameshift mutation
C. Trinucleotide repeat
D. A trisomy
E. A monosomy
Answer for Question 89
Answer: C (trinucleotide repeat)
Explanation: the large testicles are characteristic for Fragile X syndrome, in which patients can also have large ears, and which is a common cause of mental retardation, which can present as autism. Fragile X syndrome is due to CGG repeats.
QUESTION 90
A 19-year-old male who plays basketball for his college team is found dead in his dorm room by his roommate. He had an older brother who required a valve replacement and procedure on his aorta two years ago. Autopsy reveals an aortic dissection. A mutated gene for which of the following proteins was the most likely cause of his condition?
A. Elastin
B. Fibrillin
C. Keratin
D. Dystrophin
E. Titan
Answer for Question 90
Answer: B (fibrillin)
Explanation: given that he plays basketball, the assumption can be made that he is tall. Marfan syndrome is autosomal dominant, so two affected brothers is very possible. Features of Marfan syndrome include dilation of the aortic valve ring and a myxomatous mitral valve (or, clinically, mitral valve prolapse, or floppy mitral valve), which would explain the brother’s recent medical procedure. The mutation in Marfan syndrome involves the gene for fibrillin-1. Fibrillin-1 forms a scaffold for tropoelastin, but the mutation is not in the elastin gene itself. Keratin is associated with epithelium and dystrophin and titan are found in the contractile apparatus in striated muscle.
QUESTION 91
A 25-year-old male suddenly becomes short of breath while watching television with friends. Shortly thereafter, he becomes unresponsive. An ambulance is called, but, upon arrival at the emergency room, he is pronounced dead. Autopsy identifies an aortic dissection as the cause of death. The pathologist makes a diagnosis of Marfan syndrome. Which of the following features might also be expected to occur in association with this condition?
A. Short fingers
B. Pes anserinus
C. Colonic adenocarcinoma
D. Hemorrhoids
E. Kyphoscoliosis
Answer for Question 91
Answer: E (kyphoscoliosis)
Explanation: Marfan syndrome is characterized by long fingers (arachnodactyly) not short fingers. Colonic adenocarcinoma and hemorrhoids are not routinely associated with Marfan syndrome. Features of Marfan syndrome include aortic root dilation, myxomatous mitral valve, ectopia lentis, and tall stature. Patients can also have kyphoscoliosis. Pes anserinus is a normal anatomic structure.
QUESTION 92
Molecular analysis of a 10-year-old female, who was identified to have severe scoliosis, reveals a mutation in the gene for lysyl hydroxylase. Neither of her parents have a similar condition. Assuming L is for the normal allele and l is for the mutant allele, of the following, which combination best describes her parent’s genotype?
A. Father: LL; mother ll
B. Father: Ll; mother Ll
C. Father: LL; mother Ll
D. Father: LL; mother LL
Answer for Question 92
Answer: B (Father Ll; mother Ll)
Explanation: the kyphoscoliotic variant of Ehlers-Danlos is due to a mutation in lysyl hydroxylase. This version of Ehlers-Danlos is autosomal recessive, so the patient’s genotype would be ll. To produce a child with an autosomal recessive disorder, when neither of the parent’s manifest the disease, both parents would have to be carriers of the mutation, so Ll.
QUESTION 93
A 24-year-old male is playing basketball with friends when he suddenly develops chest pain. His friends drive him to the emergency room, where he is admitted and diagnosed with a myocardial infarct due to a thrombus occurring in the background of severe coronary artery atherosclerosis. Although he knew about his underlying genetic disorder, he chose to ignore it and did not ever seek treatment. Of the following, what was the mode of inheritance for his underlying condition?
A. Autosomal dominant
B. Autosomal recessive
C. Co-dominant
D. X-linked
E. Mitochondrial
Answer for Question 93
Answer: A (autosomal dominant)
Explanation: familial hypercholesterolemia is due to a mutation in the LDL receptor, which impairs the removal of LDL from the blood. Due to the high concentrations of LDL in the blood, these patients develop atherosclerosis at a young age, and, if untreated, often die of a myocardial infarct in their 20s. Familial hypercholesterolemia is autosomal dominant.
QUESTION 94
A 19-year-old male dies due to sepsis secondary to a pulmonary bacterial infection. At autopsy, sectioning of the lungs reveals plugging of the airways, dilation of airways, and an enlarged right ventricle with a thickened wall. Cultures of the lung grow Pseudomonas aeruginosa. Of the following, which is autopsy examination also likely to reveal?
A. Dilation of aortic root
B. Pancreatic islet metaplasia
C. Pancreatic acinar atrophy
D. Multiple liver hemangiomas
E. Patent ductus arteriosus
Answer for Question 94
Answer: C (pancreatic acinar atrophy)
Explanation: the clinical features are consistent with cystic fibrosis. In cystic fibrosis, mucous in the airways becomes dehydrated, as sodium re-enters cells from the lumen, and water follows. The plugged airways will lead to dilation of the airways (bronchiectasis) and increased strain on the right side of the heart, leading to right ventricular hypertrophy and possible right sided heart failure (cor pulmonale). The changes thus described in the question stem indicate that the process was chronic and not just a one-time occurrence. Pseudomonas aeruginosa is commonly associated with cystic fibrosis, and, on culture, the colonies can be very mucoid in appearance. In addition to recurrent and chronic pulmonary infections, patients with cystic fibrosis also develop pancreatic insufficiency, due to the same changes in the lung (i.e., dehydration mucous leading to plugging of ducts). As the exocrine portion of the pancreas would be impaired from secreting proto-enzymes as normal, the cells would undergo atrophy. Dilation of the aortic root is associated with Marfan syndrome, which is not associated with recurrent pulmonary infections. Liver hemangiomas are associated with von Hippel-Lindau syndrome.
QUESTION 95
A 25-year-old male is seeing his physician because of an inability to have children. His wife of four years was evaluated by her obstetrician and no conditions that would contribute to infertility were identified. After a physical examination and appropriate imaging, the man is determined to have bilateral absence of the vas deferens, which was the cause of his infertility. Of the following, he most likely has a mutation of the gene for which protein?
A. Fibrillin
B. Collagen
C. Glucocerebrosidase
D. CF transmembrane conductance regulator
E. Acid lipase
Answer for Question 95
Answer: D (CF transmembrane conductance regulator)
Explanation: while cystic fibrosis is best associated with recurrent pulmonary infections and pancreatic insufficiency, the number of mutations affecting the CFTR gene is high, and the possible phenotypes are numerous. Individuals with a mutation of the CFTR gene can survive into adulthood and be undiagnosed with the disease, until they present with infertility. In these individuals, bilateral absence of the vas deferens is a common finding.
QUESTION 96
A female neonate immediately after delivery is noted to have a distended abdomen. Forty-eight hours later, she has no passed meconium and has had an episode of bilious emesis. Of the following, what is a complication of her disease process that she will most likely develop during her lifetime?
A. Pancreatic adenocarcinoma
B. Congestive heart failure
C. Aortic dissection
D. Sinusitis
E. Glaucoma
Answer for Question 96
Answer: D (sinusitis)
Explanation: the history presented is consistent with a meconium ileus, which is a complication of cystic fibrosis. The dehydrated secretions can cause plugging of the small intestine. With blockage of the small intestine, a neonate would not pass meconium and they could have bilious emesis. Of the conditions listed, sinusitis is most commonly associated with cystic fibrosis. Due to their production of secretions that are dehydrated, and therefore, thicker and more obstructing, patients with cystic fibrosis can develop pancreatic insufficiency, biliary plugging and eventual cirrhosis, and plugging of the upper respiratory tract, leading to sinusitis.
QUESTION 97
A 25-year-old male is visiting his primary care physician. He has a history of numerous pulmonary infections during his lifetime, several with Pseudomonas aeruginosa as the causative agent. He has also had numerous episodes of diarrhea when not following his prescribed diet and medication regimen. Laboratory testing has revealed elevated concentrations of ALT and AST, and his visit today is to repeat this testing. He is concerned that he may be developing cirrhosis. Of the following, what is the inheritance pattern for his condition?
A. Autosomal dominant
B. Autosomal recessive
C. Co-dominant
D. X-linked recessive
E. X-linked dominant
Answer for Question 97
Answer: B (autosomal recessive)
Explanation: patients with cystic fibrosis often have recurrent and/or chronic pulmonary infections and most develop Pseudomonas aeruginosa. In addition, pancreatic insufficiency is a typical finding in these patients. Due to bile plugging, damage to the liver can occur, and can develop into cirrhosis. Cystic fibrosis is an autosomal recessive disorder.
QUESTION 98
A mother brings her child to an acute care clinic. Her and her husband delivered the child at home and have never sought medical care. The mother reports that she delivered a healthy baby boy, who was able to eat just fine; however, by about 6 months of age, her and her husband felt something was wrong. Six months later, she decided to bring her child to a doctor, as he had not talked and cannot walk. Physical examination reveals a normally developed child with pale hair and pale skin. Auscultation of the chest reveals no murmurs. Palpation of the abdomen reveals no hepatosplenomegaly. Of the following, a deficiency of which enzyme is the cause of this child’s clinical presentation?
A. CF transmembrane conductance regulator
B. Lysosomal glucosidase
C. Glucose-6-phosphatase
D. Glucocerebrosidase
E. Phenylalanine hydroxylase
Answer for Question 98
Answer: E (phenylalanine hydroxylase)
Explanation: the clinical history is consistent with phenylketonuria. If untreated, the elevated concentration of phenylalanine hinders brain development, leading to mental retardation. Patients may never walk or talk. In addition, they can have decreased pigmentation of the hair and skin. The fact that the mother and her husband delivered at home and received no medical care is important, as, neonatal screening will normally detect patients with phenylketonuria, and a phenylalanine free diet can be started and the patients will develop normally. CF transmembrane conductance regulator is associated with cystic fibrosis, which is not associated with neurological conditions. Lysosomal glucosidase is deficient in Pompe’s disease, which affects the heart. Glucose-6-phosphatase is deficient in von Gierke’s disease, which primarily affects the liver and would be associated with hepatomegaly. Glucocerebrosidase is deficient in people with Gaucher disease, which, in most cases, does not involve the central nervous system, and is not associated with the decreased pigmentation.
QUESTION 99
A mother brings her 2-year-old son to an acute care clinic. She explains that she delivered her child at home and has never received medical care; however, her son has not gained weight as she expected, sometimes shakes, and has difficulty walking. Physical examination reveals an enlarged liver. A chest x-ray reveals a normal cardiac silhouette. Examination of the eyes reveals no abnormalities. Of the following, which enzyme is most likely deficient?
A. Glucose-6-phosphatase
B. Muscle phosphorylase
C. Lysosomal glucosidase
D. Galactose-1-phosphate uridyltransferase
Answer for Question 99
Answer: A (glucose-6-phosphatase)
Explanation: a deficiency of glucose-6-phosphatase (von Gierke disease) leads to hypoglycemia, which can induce seizures, and can result in delayed motor development. Patients have hepatomegaly and failure to thrive. Muscle phosphorylase is deficient in McArdle disease, which usually presents in adulthood due to muscle weakness, muscle cramps, and exercise intolerance, and which involves the skeletal muscle only, and therefore would not be associated with hepatomegaly. Lysosomal glucosidase is deficient in Pompe disease, which characteristically affects the heart, causing cardiomegaly. A mild hepatomegaly can also be found in these patients. While deficiency of galactose-1-phosphate uridyltransferase is associated with hepatomegaly and can cause some neurologic changes, cataracts usually occur, and patients often have vomiting or diarrhea after drinking milk.
QUESTION 100
A mother brings her 6-month-old male infant to the pediatrician. She reports that over the past two months, she had had increasing difficulty feeding her baby, and, despite attempts, cannot get her child to stand; she also feels her child is more floppy than he should be. Physical examination reveals an enlarged liver. A chest x-ray reveals an enlarged cardiac silhouette. The child is <10% of age for height and weight. Of the following, what is the most likely enzyme deficiency?
A. Glucose-6-phosphatase
B. Muscle phosphorylase
C. Phenylalanine hydroxylase
D. Lysosomal glucosidase
E. Glucocerebrosidase
Answer for Question 100
Answer: D (lysosomal glucosidase)
Explanation: in patients with deficient lysosomal glucosidase (Pompe disease), they can, when they present early, have liver enlargement, heart enlargement, and can present with feeding difficulties, failure to thrive, and can be hypotonic. Variable terms used for the enzyme are lysosomal glucosidase, α-1,4-glucosidase, and acid maltase). Glucose-6-phosphatase is deficient in von Gierke disease,which affects the liver and leads to hypoglycemia, but does not affect the heart. Phenylalanine hydroxylase has mostly neurological findings, and would not be associated with the heart and liver enlargement. Glucocerebrosidase in most cases does involve the liver, and can, in some cases, involve the central nervous system, but does not involve the heart.
QUESTION 101
A 12-year-old male is brought to the emergency room by his parents because of sudden onset of abdominal pain, which has not resolved over the two hours. Physical examination reveals rebound tenderness and guarding. An exploratory laparotomy reveals peritonitis associated with rupture of the descending colon. Two years ago, this child had emergent surgery to repair rupture of a mesenteric artery. The underlying genetic condition is due to a mutation in the gene for production of which type of collagen?
A. Type I
B. Type II
C. Type III
D. Type IV
Answer for Question 101
Answer: C (Type III).
Explanation: this child has the vascular form of Ehlers-Danlos, which is characterized by rupture of vessels and of the colon. The wall of blood vessels and the colon contains a significant amount of type III collagen, and thus, abnormal type III collagen can predispose to rupture of these organs.