[MCQs] Neurosensory and Neuromuscular System Quiz - Part 2 (16 test)

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Neurosensory and Neuromuscular System - Neurology, Ophthalmology, Otolaryngology Part 2 (16 test)

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Question 1

A 22-year-old Caucasian female with no family history of color blindness (MIM*304000) marries a color-blind male. What is the risk for this couple of having a son or daughter who is color-blind?

A	100%
B	75%
C	50%
D	25%
E	Virtually 0

Question 1 Explanation:

The common forms of color blindness are X-linked recessive, as indicated by the initial 3 of the McKusick number (MIM*304000). The couple’s daughters will be obligate carriers—that is, carriers implied by the pedigree. Using a lowercase c to represent the recessive color blindness allele, the female is most likely XCXC, while her husband is XcY. The Punnett square below indicates that all daughters will be carriers (XcXC), while sons will be normal (XCY). Note again that loci on the X chromosome cannot be transmitted from father to son, since the son receives the father’s Y chromosome.

Question 2

A family presents with an unusual type of foot-drop and lower leg atrophy that is unfamiliar to their physician. The pedigree below is obtained. Based on the pedigree, what is the risk of individual III-3 having an affected child?

A	100%
B	75%
C	50%
D	25%
E	Virtually 0

Question 2 Explanation:

Autosomal dominant inheritance is suggested by the pedigree because of the vertical pattern of affected individuals and the affliction of both sexes. Autosomal recessive inheritance is ruled out by transmission through three generations, and X-linked recessive inheritance is made unlikely by the presence of affected females. Maternal inheritance should demonstrate transmission to all or most offspring of affected mothers. Polygenic or multifactorial inheritance is not associated with such a high frequency of transmission. Note that X-linked dominant inheritance would also be an explanation for the pedigree. Because the most likely mechanism responsible for the pedigree is autosomal or X-linked dominant inheritance, individual III-3 in the figure accompanying the question is affected with the disorder, and she has a 50% risk of transmitting the disease. Discrimination between autosomal and X-linked dominant inheritance could be made by noting the offspring of affected males, such as individual III-4. If X-linked dominant inheritance were operative, affected males would have normal sons and affected daughters. The likely diagnosis is an autosomal dominant form of Charcot-Marie-Tooth disease (MIM*118200). Charcot-MarieTooth disease exhibits genetic heterogeneity and can exhibit autosomal dominant, autosomal recessive (MIM*214380), and X-linked inheritance (MIM*302800). Note that the physician could provide counseling based on knowledge of genetics even though the disease is unfamiliar.

Question 3

A 3-year-old Caucasian boy is evaluated by an ophthalmologist and is found to have retinitis pigmentosa, a disorder characterized by pigmentary granules in the retina and progressive vision loss. The pedigree below is obtained and the family comes in for counseling. What is the risk for individual II-2 of having an affected child if he impregnates an unrelated female?

A	100%
B	75%
C	50%
D	25%
E	Virtually 0

Question 3 Explanation:

The presence of consanguinity (double line in the figure) is a red flag for autosomal recessive inheritance because, although disease-causing alleles are rare, the probability of a homozygous individual escalates dramatically when the same rare allele descends through two branches of a family. Using a lowercase r to denote the retinitis pigmentosa allele, the affected male (individual II-2 in the figure accompanying the question) has a genotype of rr. His prospective mate has a very low risk to be a carrier for this rare disease, making her genotype RR. Their children will all have genotypes Rr, making them carriers but not affected. Retinitis pigmentosa is another disease manifesting genetic heterogeneity, with autosomal dominant (MIM*180100), autosomal recessive (MIM*268000), and X-linked recessive (MIM*312650) forms. Carriers of autosomal recessive diseases are heterozygotes with one normal and one abnormal allele. Many autosomal recessive diseases involve enzyme deficiencies, indicating that 50% levels of enzymes found in heterozygotes are sufficient for normal function. The probability that an affected individual will encounter a mate who is a carrier is approximately twice the square root of the disease incidence. This figure derives from the Hardy-Weinberg law, where p is the frequency of the normal allele, and q the frequency of the abnormal allele (p + q = 1). The frequency of homozygous normal individuals is thus p2, that of heterozygotes 2pq, and that of homozygous abnormal q2 the frequency of heterozygotes. Since most recessive diseases have incidences lower than 1 in 100,000 (q2), the risk for unrelated mates to be carriers is less than 1 in 50 (2pq), and the chance of having an affected child is less than 1/50 × ¼ = less than 1 in 200. Disorders that are fairly common in certain ethnic groups, such as cystic fibrosis, are exceptions to this very low risk.

Question 4

A 6-month-old Caucasian boy of Ashkenazi Jewish origin plateaus in his development, exhibits a “startle” response to hand-claps, and is noted to have a central red area in his retina surrounded by white (cherry red spot). His physician suspects autosomal recessive Tay-Sachs disease (MIM*272800) and initiates evaluation that demonstrates deficiency of the lysosomal enzyme hexaminidase A. This deficiency leads to accumulation of complex glycolipids in brain and produces a ring of white, lipid-infiltrated cells around normal central retina (the macula). What is the risk that the grandmother of an affected child is a carrier (heterozygote) for Tay- Sachs disease?

A	100%
B	67%
C	50%
D	25%
E	Virtually 0

Question 4 Explanation:

Inborn errors of metabolism often reflect enzyme deficiencies with resulting autosomal recessive inheritance. Parents of children with autosomal recessive disorders are obligate carriers if nonpaternity and rare examples of uniparental disomy (inheritance of both chromosomal homologues from the same parent) are excluded. Normal siblings have a two-thirds chance of being carriers because they cannot be homozygous for the abnormal allele. Grandparents have a one-half chance of being carriers because one or the other must have transmitted the abnormal allele to the obligate carrier parent. First cousins share a set of grandparents of whom one must be a carrier. There is a one-half chance for the aunt or uncle to be a carrier and a one-fourth chance for the first cousin. Half-siblings share an obligate carrier parent and have a one-half chance of being carriers. These calculations assume a lack of new mutations and a lack ofcoincidental alleles (lessened if the parents are not related but of concern in certain Jewish communities where carrier rates for Tay-Sachs can be high).

Question 5

A 1-month-old Caucasian male infant is being considered for adoption, and his older half sister is known to have developed hydrocephalus, an accumulation of cerebrospinal fluid in the brain ventricles. Hydrocephalus is a multifactorial disorder, and the prospective parents wish to know the chance the boy will develop hydrocephalus. In order to estimate this risk, the physician must determine what proportion of genes the brother and the half sister have in common. What is this proportion?

A	1
B	1/2
C	1/4
D	1/8
E	1/16

Question 5 Explanation:

Although all individuals, other than identical twins, are genetically unique, each individual will have some genes in common with their relatives. The more closely related, the more genes the individuals have in common. First-degree relatives, such as siblings, parents, and children, share one-half of their genes. Second-degree relatives share one-fourth, and third-degree relatives share one-eighth. Full siblings will have half their genes in common, half siblings (with only one common parent) one-fourth. Risks for multifactorial disorders such as hydrocephalus fall off rapidly with decreasing degrees of relationship, with average figures of 3% to 5% for first-degree relatives (sharing one-half their genes), 0.5% to 0.7% for second-degree relatives (sharing one-fourth their genes as for this child and his sister), and dropping to near baseline incidence (1-3 per thousand for congenital anomalies) for third-degree relatives like first cousins.

Question 6

A 66-year-old African American female is diagnosed with Parkinson disease (PD-MIM*168601) and there are no other cases in her family. She requests genetic counseling and/or testing to assess risks that her middleaged children will develop parkinsonism. Her physician explains that 1% of people over 50 may contract the disease, that rare families exhibit autosomal dominant inheritance, and that usual risks are increased three-to fourfold for first-degree relatives of affected individuals. Based on this information, which of the following options provide appropriate genetic counseling for this patient?

A	Likely multifactorial determination in your family with a 3% to 4% risk for your middle-aged children to develop PD
B	Likely multifactorial determination in your family with a 1% risk for your middle-aged children to develop PD
C	Likely autosomal dominant inheritance in your family with a 50% risk for your middle-aged children to develop PD
D	Likely autosomal dominant inheritance in your family with a 25% risk for your middle-aged children to develop PD
E	Likely multifactorial determination in your family with a 10% risk for your middle-aged children to develop PD

Question 6 Explanation:

The data indicate that Parkinson disease (PD-MIM*168601) exhibits multifactorial determination with rare families showing autosomal dominant inheritance; the patient could represent a new mutation for the rare dominant form but most likely has multifactorial disease (incorrect answers c-e). First-degree relatives (parent-child, siblings) share 50% of their genes, giving the female’s children a 3% to 4% risk to develop PD (3-4 times the baseline 1% risk, incorrect answer b). Were the female a rare example of mutation for autosomal dominant PD, each child would have a 50% risk to inherit her abnormal PD allele (not 25 as in incorrect answer d) and be affected (and a 50% risk to inherit her normal allele, with a background 1% risk to be affected). Genetic counseling is fundamentally an educational process in which the physician discusses likely inheritance risks, potential testing, and reproductive options. Because humans have small family sizes, genetic information is often incomplete and requires judgment about likelihood. Genetic counseling always depends upon a correct medical diagnosis. In the case of common multifactorial diseases such as PD, DNA testing for rare mutations like that in the α-synuclein gene (MIM*168601) might be performed to exclude autosomal dominant inheritance. Another approach is to search for DNA markers (eg, single nucleotide polymorphisms = SNPs that occur every 2-300 bp in human DNA) that allows modification of risk for multifactorial PD. The connection of PD with low CNS dopamine levels prompted a successful search for SNPs near loci encoding enzymes of the phenylalanine/tyrosine/catecholamine/dopamine pathway that serve as DNA markers for risk modification. Current research approaches to complex diseases include genome-wide searches for single nucleotide polymorphisms (SNPs occurring every 2-300 bp in human DNA) that associate with the phenotype. Given the connection of Parkinson disease with low dopamine, looking at SNPs near loci encoding enzymes of the phenylalanine/tyrosine/catecholamine/dopamine pathway would be a reasonable start. If a G for C nucleotide substitution was present in a certain allele, and a majority of those with Parkinson disease were G/G homozygotes or G/C heterozygotes, then the G SNP becomes a DNA marker for parkinsonism susceptibility— more than 10 such loci have been found (MIM*168601). Another approach is to examine rare familial forms of parkinsonism (eg, MIM*168601) for insights into disease causation, just as study of familial hypercholesterolemia (MIM*144010) highlighted elevated cholesterol as a risk factor for coronary artery disease.

Question 7

In the operating room, a 5-year-old Hispanic boy receives succinylcholine as a muscle relaxant to facilitate intubation and anesthesia. The operation proceeds until it is time for recovery, when the child does not begin breathing. A hurried discussion with the father discloses no additional problems in the family, but he does say that he and his wife are first cousins. Which of the following is the most likely possibility?

A	An autosomal dominant disorder that interferes with succinylcholine metabolism
B	An autosomal recessive disorder that interferes with succinylcholine metabolism
C	An X-linked disorder that interferes with succinylcholine metabolism
D	A lethal gene transmitted through consanguinity that affects the respiratory system
E	Mismanagement of halothane anesthesia during the operation

Question 7 Explanation:

Unusual reactions to drugs targeting enzymes may be mediated by autosomal recessive mutations, regardless of anesthetic management (incorrect answers a-c, e). Succinylcholine is metabolized by a plasma enzyme formerly called pseudocholinesterase (now called butyrylcholinesterase [BChE] to designate its favored substrate). Approximately 1 in 100 individuals are homozygous for a variant of BChE that has 60% activity, whereas 1 in 150,000 individuals are homozygous for a variant with 33% activity. The latter group exhibits prolonged recovery from succinylcholine-induced anesthesia, a phenotype known as succinylcholine apnea (MIM*177400). As with most enzyme defects, succinylcholine apnea exhibits autosomal recessive inheritance. The parents will be heterozygous for a BChE variant but have not undergone anesthesia to display the phenotype.

Question 8

Pharmacogenetics, or the study of drug-induced disease due to genetic variation, is receiving increased attention particularly with regard to population or at least preoperative screening. The frequency of heterozygotes for variant butyrylcholinesterase (BChE) alleles in Caucasians is about 4 per 100, implying an incidence of individuals with potential for severe apnea of which of the following?

A	1 in 5000
B	1 in 2500
C	1 in 1250
D	1 in 500
E	1 in 50

Question 8 Explanation:

The Hardy-Weinberg law specifies that the distribution of genotypes, given frequencies of normal (p) and abnormal (q) alleles in an ideal population, will be p2 for homozygous normal, 2pq for heterozygotes, and q2 for homozygous abnormal. If the heterozygote frequency for butyrylcholinesterase variant alleles is 4 per 100 = 2pq, then pq = 2/100. Since the frequency of abnormal alleles (q) is usually much less than that of normal (p), one can approximate p to 1 and assume q = 2 per 100 with q = 4/10,000 or 1 in 2500. As a simplification, one can calculate carrier rates as the square root of disease incidence for autosomal recessive disorders. The proportion of individuals with susceptibility to severe consequences of anesthesia (1 in 2500) is similar to frequencies of common genetic diseases in Caucasians like cystic fibrosis (MIM*219700) and certainly deserves consideration for genetic screening.

Question 9

A 6-month-old Caucasian girl of Ashkenazi Jewish background seems to plateau in development after a normal gestation, delivery, and early infancy. She rolled over well with smiling and good interaction but became less active and does not maintain a sit. Her pediatrician notes low muscle tone and claps her hands to elicit an exaggerated extension of her arms (Moro reflex—enhanced startle response). Ophthalmologic examination reveals a central red area of the retina surrounded by white tissue (cherry red spot). A diagnosis of lipid storage disease (neurolipidosis) is suspected. If the diagnosis is correct, what is the risk that the next child of these parents will be affected with the same disease?

A	1/2
B	1/4
C	3/4
D	1/12
E	1/24

Question 9 Explanation:

Metabolic diseases usually exhibit autosomal or X-linked recessive inheritance with autosomal disease likely in this female patient. The child’s parents are obligate carriers and there is a one-fourth chance (25% recurrence risk) that their next child will be affected (incorrect answers a, c-e). The symptoms suggest Tay-Sachs disease (MIM*272800), an autosomal recessive disorder involving neurodegeneration and early death that has a higher frequency in Ashkenazi Jewish populations.

Question 10

The cause of Tay-Sachs disease (MIM*272800) is best described by which of the following?

A	Excess of a lysosomal enzyme in blood due to defective uptake
B	Deficiency of a lysosomal enzyme that digests proteoglycans
C	Deficiency of a membrane receptor that takes up proteoglycans
D	Deficiency of a mitochondrial enzyme that degrades glycogen
E	Deficiency of a mitochondrial triglyceride lipase

Question 10 Explanation:

The lysosomal enzyme hexosaminidase A is deficient in Tay-Sachs disease. The enzyme cleaves aminohexose groups from gangliosides, complex lipids formed from ceramide (a derivative of sphingosine). Ceramide is synthesized in the endoplasmic reticulum from palmitoyl coenzyme A (16-carbon acyl-CoA) and serine in a reaction catalyzed by pyridoxal phosphate. Uridine diphosphoglucose (UDP-glucose) or UDP-galactose moieties and sialic acid groups are then added in the Golgi apparatus and the gangliosides contribute to myelin in nerve cells. Neurolipidoses like Tay-Sachs disease lack certain lysosomal enzymes necessary to degrade the gangliosides, causing severe effects on nerve cells (neurodegeneration). A parallel group of disorders called mucopolysaccharidoses result from the absence of lysosomal enzymes that degrade complex carbohydrate chains and their associated proteins (called proteoglycans). Proteoglycans are more widely distributed than gangliosides, occurring in the ground substance of many tissues. Accumulation of the glycosaminoglycans from these proteoglycans thus causes a wide spectrum of symptoms including coarsening of the face and hair, cardiopulmonary problems, and bony deformities such as kyphosis (beaked spine). There is a specific lysosomal receptor that recognizes mannose 6-phosphate on certain lysosomal enzymes and targets them to lysosomes. Mutations in this receptor can cause increased blood levels and lysosomal deficiencies of several enzymes that are normally targeted to lysosomes. One such disease is I (inclusion) cell disease (MIM*252500). The slow accumulation of abnormal gangliosides in lipidoses and of abnormal proteoglycans in mucopolysaccharidoses causes a characteristic clinical course of normal early development that plateaus and then regresses. The age of regression and life span vary widely among the lysosomal storage diseases, with Tay-Sachs being one of the most severe.

Question 11

The frequency of carriers of Tay-Sachs disease (MIM*272800) in Ashkenazi Jewish populations is 1 in 30. Some Jewish communities offer carrier testing for young adults so they will know their status before marriage. A known carrier female becomes involved with an exchange student from Russia who also is Ashkenazi Jewish but who has not had carrier testing. What is the chance that a child of this union will have Tay-Sachs disease?

A	1 in 2 1/120
B	1 in 15 1/240
C	1 in 30 1/3600
D	1 in 60 1/9000
E	1 in 120 1/36,000

Question 11 Explanation:

The female is a known carrier of Tay-Sachs disease (MIM*272800) and thus has one normal and one Tay-Sachs allele. The male has a 1 in 30 chance to have this same genotype. Each will have a 1 in 2 chance to transmit their abnormal allele to a future child, giving a joint probability of ½ × ½ × 1/30 = 1/120 (answers a-d incorrect). The joint probability of two or more independent events equals theproduct of their separate probabilities.

Question 12

A couple decide to have prenatal diagnosis because their previous child has Tay-Sachs disease (MIM*272800). Which of the following prenatal diagnostic techniques is optimal for fetal diagnosis?

A	Chorionic villus sampling (CVS)
B	Percutaneous umbilical blood sampling
C	Amniotic fluid α-fetoprotein levels
D	Maternal serum α-fetoprotein (MSAFP)
E	Fetal x-rays

Question 12 Explanation:

Most enzymes are expressed in chorionic villi or amniocytes and allow prenatal diagnosis of metabolic disorders through cell culture and enzyme assay. Percutaneous umbilical blood sampling (PUBS), or cordocentesis, offers another strategy if the enzyme is normally present in leukocytes. However, transabdominal aspiration of the umbilical cord is difficult and must be performed later in pregnancy (18+ weeks), with higher risks for inducing abortion (∼5%) than CVS (8-10 weeks gestation, ∼2-3%), or amniocentesis (14-16 weeks gestation), less than 1 in 1000 risk when performed with ultrasound guidance. Fetal tissues produce α-fetoprotein (AFP) and this protein does not cause any metabolic disorders but is used as an index of fetal tissue differentiation and integrity. Amniotic or maternal serum α-fetoprotein (MSAFP) is most often used to detect, respectively, neural tube defects or chromosomal disorders and would not be useful in a case of normal fetal development with hexosaminidase A deficiency. Measure of α-fetoprotein in maternal serum is combined with two to three other markers (estriol, human chorionic gonadotropin, α-inhibin) that constitute the triple test or quad screen used to indicate higher risks for fetal chromosome disorders.

Question 13

A 2-year-old child is hospitalized for evaluation of poor growth and low muscle tone. The most striking physical finding is unruly, “kinky” hair, but the child also has increased joint laxity and thin skin. Which of the following laboratory findings is most likely?

A	High ceruloplasmin
B	High tissue copper
C	Low serum iron
D	Low saturation of transferrin
E	Low serum haptoglobin

Question 13 Explanation:

This child’s kinky hair is a symptom of Menke disease, an alteration in a copper-binding ATPase. Dysfunction of the ATPase imprisons copper in cells and prevents its normal absorption from the intestine. Enzymes that use copper as cofactor have diverse roles in metabolism, including some that modify and degrade amino acids in collagen. This accounts for the connective tissue symptoms (lax joints, thin skin) in Menke disease. Wilson disease (MIM*277900) is also caused by mutations in a copper-binding ATPase that lead to copper storage in the eye (Kayser-Fleischer ring of corneal depositions that give a greenish-brown ring around the iris), liver (causing hepatitis and cirrhosis), and the brain (sometimes causing psychosis). Ceruloplasmin, the major copper transporter in serum, is decreased in both diseases.

Question 14

A male child presents with delayed development and scarring of his lips and hands. His parents have restrained him because he obsessively chews on his lips and fingers. Which of the following is likely to occur in this child?

A	Increased levels of 5-phosphoribosyl-1-pyrophosphate (PRPP)
B	Decreased purine synthesis
C	Decreased levels of uric acid
D	Increased levels of hypoxanthine-guanosine phosphoribosyl transferase (HGPRT)
E	Increased levels of hypoxanthine-guanosine phosphoribosyl transferase (HGPRT)

Question 14 Explanation:

The child has Lesch-Nyhan syndrome (MIM*308000), an X-linked recessive disorder that is caused by HGPRT enzyme deficiency. HGPRT is responsible for the salvage of purines from nucleotide degradation, and its deficiency elevates levels of PRPP, purine synthesis, and uric acid. PRPP is also elevated in glycogen storage diseases due to increased amounts of carbohydrate precursors. The medication allopurinol is used to inhibit purine pathways in gout so as to lower the accumulating uric acid.

Question 15

The figure below shows a pedigree that includes individuals with Charcot-Marie-Tooth disease (CMT), a neurologic disorder that produces dysfunction of the distal extremities with characteristic footdrop. If individual III-4 becomes pregnant, what is her risk of having a child with CMT?

A	1/2
B	1/4
C	1/8
D	1/16
E	Virtually 0

Question 15 Explanation:

The predominance of affected males with transmission through females makes this pedigree (figure below Question 361) diagnostic of X-linked recessive inheritance. Individual I-1 is an obligate carrier, as demonstrated by her affected son and grandson. Individual II-2 cannot transmit an X-linked disorder, although his daughters are obligate carriers. Individual II-3 must be a carrier because of her affected son, which results in a onefourth probability of recurrence of CMT in her offspring. Individual II-5 has a one-half probability of being a carrier with a one-eighth probability for affected offspring. Individual III-4 also has a one-eighth probability of being a carrier; her risk for affected offspring is also one-eighth despite the consanguineous marriage. Individual III-8 has a one-fourth chance of being a carrier and a one-sixteenth chance of having affected offspring. CMT is one of the disorders exhibiting genetic heterogeneity, with autosomal dominant (MIM*118200), autosomal recessive (MIM*214380), and X-linked recessive (MIM*302800) forms.

Question 16

A child with severe epilepsy, autistic behavior, and developmental delay has characteristics of a condition known as Angelman syndrome (MIM*105830). Because of the syndromic nature of the disorder and the developmental delay, a karyotype is performed that shows a missing band on one chromosome 15. Which of the following best describes this abnormality?

A	Interstitial deletion of 15
B	Terminal deletion of 15
C	Pericentric inversion of 15
D	Paracentric inversion of 15
E	15q–

Question 16 Explanation:

A missing band suggests an interstitial (internal) deletion rather than removal of the distal short or long arm (known as a terminal deletion). The shorthand notation 15q– implies a terminal deletion of the long arm of chromosome 15. Pericentric (surrounding the centromere) or paracentric (not including the centromere) inversions result from crossover of a chromosome with itself and then breakage and reunion to produce an internal inverted segment. Interstitial deletion 15q11q13 is seen in approximately 60% of patients with Prader-Willi and 5% of patients with Angelman syndromes. Other patients with these syndromes inherit both chromosomes 15 from their mother (Prader-Willi) or both from their father (Angelman), a situation known as uniparental disomy. Genomic imprinting of the 15q11q13 region is different on the chromosome inherited from the mother than on the chromosome inherited from the father. The normal balance of maternal and paternal imprints is thus disrupted by deletion or uniparental disomy, leading to reciprocal differences in gene expression that present as Angelman or Prader-Willi syndromes.

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II. Preview all questions below

1. A 22-year-old Caucasian female with no family history of color blindness (MIM*304000) marries a color-blind What is the risk for this couple of having a son or daughter who is color-blind?

100%
75%
50%
25%
Virtually 0

2. A family presents with an unusual type of foot-drop and lower leg atrophy that is unfamiliar to their physician. The pedigree below is Based on the pedigree, what is the risk of individual III-3 having an affected child?

100%
75%
50%
25%
Virtually 0

3. A 3-year-old Caucasian boy is evaluated by an ophthalmologist and is found to have retinitis pigmentosa, a disorder characterized by pigmentary granules in the retina and progressive vision loss. The pedigree below is obtained and the family comes in for What is the risk for individual II-2 of having an affected child if he impregnates an unrelated female?

100%
75%
50%
25%
Virtually 0

4. A 6-month-old Caucasian boy of Ashkenazi Jewish origin plateaus in his development, exhibits a “startle” response to hand-claps, and is noted to have a central red area in his retina surrounded by white (cherry red spot). His physician suspects autosomal recessive Tay-Sachs disease (MIM*272800) and initiates evaluation that demonstrates deficiency of the lysosomal enzyme hexaminidase This deficiency leads to accumulation of complex glycolipids in brain and produces a ring of white, lipid-infiltrated cells around normal central retina (the macula). What is the risk that the grandmother of an affected child is a carrier (heterozygote) for Tay- Sachs disease?

100%
67%
50%
25%
Virtually 0

5. A 1-month-old Caucasian male infant is being considered for adoption, and his older half sister is known to have developed hydrocephalus, an accumulation of cerebrospinal fluid in the brain Hydrocephalus is a multifactorial disorder, and the prospective parents wish to know the chance the boy will develop hydrocephalus. In order to estimate this risk, the physician must determine what proportion of genes the brother and the half sister have in common. What is this proportion?

1
½
¼ d.
1/8
1/16

6. A 66-year-old African American female is diagnosed with Parkinson disease (PD-MIM*168601) and there are no other cases in her family. She requests genetic counseling and/or testing to assess risks that her middleaged children will develop Her physician explains that 1% of people over 50 may contract the disease, that rare families exhibit autosomal dominant inheritance, and that usual risks are increased three-to fourfold for first-degree relatives of affected individuals. Based on this information, which of the following options provide appropriate genetic counseling for this patient?

Likely multifactorial determination in your family with a 3% to 4% risk for your middle-aged children to develop PD
Likely multifactorial determination in your family with a 1% risk for your middle-aged children to develop PD
Likely autosomal dominant inheritance in your family with a 50% risk for your middle-aged children to develop PD
Likely autosomal dominant inheritance in your family with a 25% risk for your middle-aged children to develop PD
Likely multifactorial determination in your family with a 10% risk for your middle-aged children to develop PD

7. In the operating room, a 5-year-old Hispanic boy receives succinylcholine as a muscle relaxant to facilitate intubation and anesthesia. The operation proceeds until it is time for recovery, when the child does not begin A hurried discussion with the father discloses no additional problems in the family, but he does say that he and his wife are first cousins. Which of the following is the most likely possibility?

An autosomal dominant disorder that interferes with succinylcholine metabolism
An autosomal recessive disorder that interferes with succinylcholine metabolism
An X-linked disorder that interferes with succinylcholine metabolism
A lethal gene transmitted through consanguinity that affects the respiratory system
Mismanagement of halothane anesthesia during the operation

8. Pharmacogenetics, or the study of drug-induced disease due to genetic variation, is receiving increased attention particularly with regard to population or at least preoperative The frequency of heterozygotes for variant butyrylcholinesterase (BChE) alleles in Caucasians is about 4 per 100, implying an incidence of individuals with potential for severe apnea of which of the following?

1 in 5000
1 in 2500
1 in 1250
1 in 500
1 in 50

9. A 6-month-old Caucasian girl of Ashkenazi Jewish background seems to plateau in development after a normal gestation, delivery, and early She rolled over well with smiling and good interaction but became less active and does not maintain a sit. Her pediatrician notes low muscle tone and claps her hands to elicit an exaggerated extension of her arms (Moro reflex—enhanced startle response). Ophthalmologic examination reveals a central red area of the retina surrounded by white tissue (cherry red spot). A diagnosis of lipid storage disease (neurolipidosis) is suspected. If the diagnosis is correct, what is the risk that the next child of these parents will be affected with the same disease?

½
¼
¾
1/12
1/24

10. The cause of Tay-Sachs disease (MIM*272800) is best described by which of the following?

Excess of a lysosomal enzyme in blood due to defective uptake
Deficiency of a lysosomal enzyme that digests proteoglycans
Deficiency of a membrane receptor that takes up proteoglycans
Deficiency of a mitochondrial enzyme that degrades glycogen
Deficiency of a mitochondrial triglyceride lipase

11. The frequency of carriers of Tay-Sachs disease (MIM*272800) in Ashkenazi Jewish populations is 1 in Some Jewish communities offer carrier testing for young adults so they will know their status before marriage. A known carrier female becomes involved with an exchange student from Russia who also is Ashkenazi Jewish but who has not had carrier testing. What is the chance that a child of this union will have Tay-Sachs disease?

1 in 2 1/120
1 in 15 1/240
1 in 30 1/3600
1 in 60 1/9000
1 in 120 1/36,000

12. A couple decide to have prenatal diagnosis because their previous child has Tay-Sachs disease (MIM*272800). Which of the following prenatal diagnostic techniques is optimal for fetal diagnosis?

Chorionic villus sampling (CVS)
Percutaneous umbilical blood sampling
Amniotic fluid α-fetoprotein levels
Maternal serum α-fetoprotein (MSAFP)
Fetal x-rays

13. A 2-year-old child is hospitalized for evaluation of poor growth and low muscle tone. The most striking physical finding is unruly, “kinky” hair, but the child also has increased joint laxity and thin skin. Which of the following laboratory findings is most likely?

High ceruloplasmin
High tissue copper
Low serum iron
Low saturation of transferrin
Low serum haptoglobin

14. A male child presents with delayed development and scarring of his lips and hands. His parents have restrained him because he obsessively chews on his lips and Which of the following is likely to occur in this child?

Increased levels of 5-phosphoribosyl-1-pyrophosphate (PRPP)
Decreased purine synthesis
Decreased levels of uric acid
Increased levels of hypoxanthine-guanosine phosphoribosyl transferase (HGPRT)
Glycogen storage

15. The figure below shows a pedigree that includes individuals with Charcot-Marie-Tooth disease (CMT), a neurologic disorder that produces dysfunction of the distal extremities with characteristic If individual III-4 becomes pregnant, what is her risk of having a child with CMT?

½
¼ 1/8
1/16
Virtually 0

16. A child with severe epilepsy, autistic behavior, and developmental delay has characteristics of a condition known as Angelman syndrome (MIM*105830). Because of the syndromic nature of the disorder and the developmental delay, a karyotype is performed that shows a missing band on one chromosome Which of the following best describes this abnormality?

Interstitial deletion of 15
Terminal deletion of 15
Pericentric inversion of 15
Paracentric inversion of 15
15q–

[MCQs] Neurosensory and Neuromuscular System Quiz – Part 2 (16 test)

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Neurosensory and Neuromuscular System - Neurology, Ophthalmology, Otolaryngology Part 2 (16 test)

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