Neuromuscular disorders

Question 1

Adopted 5 yo with no ID but Gowers signs, calf hypertrophy and elevated CK. Next step for diagnosis?
A.Deletion/duplication analysis of the DMD gene
B.Next-generation sequencing all the genes related to muscular dystrophy
C. Sequencing analysis the DMD gene
D. Skeletal muscle biopsy for Western blot studies of dystrophin
E. Skeletal muscle biopsy for immunohistochemistry studies of dystrophin
F.None of the above

Answer 1

A.Deletion/duplication analysis of the DMD gene

Question 2

DMD. What is the most appropriate first tier molecular workup?
A.Multiplex ligation-dependent probe amplification
B.Next-generation sequencing analysis
C.Sanger sequencing analysis
D.TaqMan genotype assays
E.None of the above

Answer 2

A.Multiplex ligation-dependent probe amplification

X-linked dystrophin gene (about 65% deletions, about 7% duplications, about 26% point variants, and about 2% unknown variants)

Question 3

DMD. Deletion/duplication studies negative. What is the next step in the molecular workup?
A.Multiplex ligation-dependent probe amplification
B.Sanger sequencing analysis
C.TaqMan genotype assays
D.Quantitative PCR
E.None of the above

Answer 3

B.Sanger sequencing analysis

Question 4

How frequently do patients with Duchenne muscular dystrophy (DMD) have inherited pathogenic variants?
A.<1%
B.25%
C.67%
D.85%
E.>99%
F.None of the above

Answer 4

D.85%

Question 5

DMD male testing showed a frameshift deletion with mother not detected and brother detected. What is the explanation?
A.Incomplete penetrance
B.Variable expression
C.De novo mutations
D.Germline mosaicism
E.X inactivation
F.None of the above

Answer 5

D.Germline mosaicism

Question 6

DMD male testing showed a frameshift deletion with mother not detected. What is the explanation? Which one of the following would be the most approximate estimation of the recurrent risk in this family?
A.<1% B.5% C.25% D.36% E.None of the above

Answer 6

B.5%

20% germline mosaicism x 1/2 x 1/2 = 5%

Question 7

DMD out-of-frame deletion. What is likely the disease?
A.Becker muscular dystrophy (BMD)
B.Duchenne muscular dystrophy (DMD)
C.DMD-associated dilated cardiomyopathy (DCM)
D.Uncertain E.None of the above

Answer 7

B.Duchenne muscular dystrophy (DMD)

Question 8

18 yo male with calf hypertrophy and myopathic changes. In-frame deletion of exon 45-49 detected in DMD. What is the disease?
A.Becker muscular dystrophy (BMD)
B.Duchenne muscular dystrophy (DMD)
C.DMD-associated dilated cardiomyopathy (DCM)
D.Uncertain E.None of the above

Answer 8

A.Becker muscular dystrophy (BMD)

Question 9

An 8 yo male with calf hypertrophy and myopathic changes. Out-of-frame deletion of in DMD detected. What recommendation would be appropriate in the molecular genetics report?
A.Genetic counseling
B.Maternal testing
C.Paternal testing
D.Prenatal testing for future pregnancies
E.A and B
F.A and C
G.A, B, and C
H.A, B, and D
I.A, C, and D
J.A, B, C, and D

Answer 9

H.A, B, and D

Question 10

A molecular genetics study for the DMD gene detected an out-of-frame deletion, which confirmed the diagnosis of Duchenne muscular dystrophy (DMD). Which one of the following mechanisms would most likely contribute to the pathogenesis of DMD in this patient?
A.Dominant negative
B.Gain of function
C.Loss of function
D.None of the above

Answer 10

C.Loss of function

Question 11

7 mo old boy with cardiomyopathy, skeletal myopathy, neutropenia and elevated urine 3-methylglutaconic acid (3-MGC). Barth syndrome - what is the mode of inheritance?
A.Autosomal dominant
B.Autosomal recessive
C.X-linked
D.Mitochondrial inherited
E.None of the above

Answer 11

C.X-linked

TAZ- cardiolipin - XLR

Question 12

10 mo boy with familial male cardiomyopathy, elevated 3MGC, TAZ variant. What is the risk for the male patient’s future children?
A.<1%
B.25%
C.50%
D.67%
E.99%
F.Unpredictable

Answer 12

A.<1%

Question 13

First line test for Barth syndrome?
A.Deletion/duplication analysis
B.Next-generation sequencing analysis
C.Sanger sequencing analysis
D.Targeted variant analysis
E.None of the above

Answer 13

C.Sanger sequencing analysis

Question 14

Barth syndrome. Which one of the following molecular assays would most likely be used to confirm the diagnosis in this patient?
A.Deletion/duplication analysis of mtDNA
B.Sequencing analysis of mtDNA
C.Sequencing analysis of the TAZ gene
D.Sequencing analysis of the TWNK gene
E.None of the above

Answer 14

C.Sequencing analysis of the TAZ gene

Question 15

Limb-girdle atrophy in a 22 yo. What is the first-tier molecular test?
A.Chromosomal microarray study (CMA)
B.Fluorescent in situ hybridization (FISH)
C.Molecular genetic testing for DMD
D.Next-generation sequencing (NGS) for limb-girdle muscular dystrophy
E.Quantitative PCR

Answer 15

C.Molecular genetic testing for DMD

For any male or female suspected of having limb-girdle muscular dystrophy, it is necessary to first rule out an X-linked dystrophinopathy. Especially in female, the incidence of LGMD is nearly as much as that for a DMD carrier.

Question 16

First-tier test for SMA?
A.Chromosomal microarray
B.Multiplex ligation-dependent probe amplification (MLPA)
C.Next-generation sequencing analysis
D.Sanger sequencing analysis
E.Target variant analysis
F.None of the above

Answer 16

B.Multiplex ligation-dependent probe amplification (MLPA)

Question 17

Molecular testing was ordered for SMA. Which one of the following exons of SMN1 would most likely be the target of this molecular genetics study?
A.Exon 3
B.Exon 6
C.Exon 7
D.Exon 8
E.None of the above

Answer 17

C.Exon 7

The SMN region on chromosome 5q12.2-q13.3

Question 18

A deletion analysis of the SMN1/SMN2 genes revealed the presence of one copy of exon 7. Which one of the following would be the most appropriate next step in the workup to confirm or rule out the diagnosis?
A.Diagnosing the patient with spinal muscular atrophy
B.Ordering exome sequencing analysis
C.Ordering a next-generation panel with 55 genes for neuromuscular disorders
D.Ordering Sanger sequencing analysis of SMN1
E.Ordering Sanger sequencing analysis of SMN2
F.None of the above

Answer 18

D.Ordering Sanger sequencing analysis of SMN1

SMN1 (telomeric copy) and SMN2 (centromeric copy). SMN2 predominantly produces a survival motor-neuron protein that is lacking in exon 7,

SMN1 and SMN2 each comprise nine exons and differ only in eight nucleotides (five intronic; and three exonic, with one each located within exons 6, 7, and 8). Exon 7 of SMN1 is undetectable in more than 95% of individuals with SMA

Question 19

The baby died on day 12 after being disconnected from the tubes. Parental testing revealed that the mother had two copies of exon 7 and exon 8 of SMN1, but the father had one copy of exon 7 and exon 8 of SMN1. Which one of the following would be the most appropriate explanation of this result?
A.It is likely both the couple were carriers of a deletion in SMN1.
B.It is likely that the mother had a germline mosaicism for a heterozygous deletion of exon 7 in SMN1.
C.The proband and his elder brother had a de novo heterozygous deletion of exon 7 in SMN1.
D.The mother had a pathogenic variant, which may be detected by Sanger sequencing analysis.
E.All of the above.
F.None of the above.

Answer 19

A.It is likely both the couple were carriers of a deletion in SMN1.

Approximately 6% of parents of a child with spinal muscular atrophy (SMA) resulting from a homozygous SMN1 deletion have normal results of SMN1 dosage testing in one of the parents for the following two reasons. About 4%–8% of carriers have two copies of SMN1 on a single chromosome. These carrier individuals with two copies of SMN1 on one chromosome (a [2+0] genotype) are misdiagnosed as noncarriers by the SMN1 dosage test; this is a false negative test result. A specific haplotype block is associated with a [2+0] genotype in the Ashkenazi Jewish population.

Question 20

Genetics studies for myotonic dystrophy type 1 were negative, but he had a homozygous deletion of exon 7 and a heterozygous deletion of exon 8 of survival motor neuron gene 1 (SMN1). Parental testing revealed that the mother had two copies of exon 7 and exon 8 of SMN1, but the father had one copy of exon 7 and exon 8 of SMN1. The physician suspected that the mother had a specific haplotype block, [2+0], due to a founder effect in Ashkenazi Jews. Which one of the following would be an appropriate way to confirm it?

A.Chromosomal microarray
B.Linkage study
C.No need to confirm
D.Southern blot
E.Testing the mother’s parents
F.None of the above

Answer 20

E.Testing the mother’s parents

Question 21

SMN infant. Genetics studies for myotonic dystrophy type 1 were negative, but he had a homozygous deletion of exon 7 and a heterozygous deletion of exon 8 of survival motor neuron gene 1 (SMN1). The baby died on day 12 after being disconnected from the tubes. Parental testing revealed that the husband had one copy of exon 7 of the SMN1 gene, but the wife had none. Which one of the following would be the most appropriate study as the next step in the workup?
A.Redesigning the primers and repeat the study with the new primers
B.Requesting another specimen from the mother
C.Testing the maternal grandparents of the proband
D.Testing the copy number changes of SMN2 in the wife
E.None of the above

Answer 21

D.Testing the copy number changes of SMN2 in the wife

five copies of the SMN2 genes may be sufficient to compensate for the absence of the SMN1 gene.

rare exon splicing enhancer element can make SMN2 fully functional with exon 7 inclusion

plastin 3 (encoded by PLS3 at chromosome locus Xq23) may also compensate

Question 22

The detection rate of SMA varies by ethnicity, ranging from 71% in African Americans to 95% in Caucasians. What is the major contributor to this ethnicity-based variation in detection rate?
A.The occurrence of two (or more) SMN1 genes in tandem on a single chromosome 5
B.The occurrence of two (or more) SMN2 genes in tandem on a single chromosome 5
C.The occurrence of two (or more) SMN1 and SMN2 genes in tandem on a single chromosome 5
D.The occurrence of pathogenic point mutations in SMN1 on chromosome 5

Answer 22

A.The occurrence of two (or more) SMN1 genes in tandem on a single chromosome 5

Question 23

Which of the following is true about SMA?
A.There are two inverted SMN copies on chromosome 5q, and SMN1 is at the centromeric side.
B. the SMN2 is the SMA-determining gene
C. The SMN2 gene produces more full-length transcript than SMN1
D.The number of SMN2 copies has been shown to modulate the clinical phenotype.
E.SMN2 exon 7 is absent in the majority of patients, independent of the severity of SMA.
F.The coding sequence of SMN2 differs from that of SMN1 by a SNP (840C<T), which alters the amino acid sequence.

Answer 23

D.The number of SMN2 copies has been shown to modulate the clinical phenotype.

Question 24

Which one of the following populations has the highest carrier frequency of spinal muscular atrophy (SMA)?
A.African American
B.Ashkenazi Jewish
C.Asian
D.Caucasian
E.Hispanic

Answer 24

D.Caucasian

Question 25

AJ preconception counseling. Mother has three copies in exon 7 of SMN1 for spinal muscular atrophy (SMA). Which one of the following may be the most appropriate interpretation? A. The wife is not a carrier of SMA. B. The wife has reduced risk to be a carrier. C. The results must be wrong, and need to be repeated. D. The sample is mixed with other sample(s), and another blood draw is needed.

Answer 25

B. The wife has reduced risk to be a carrier.

Question 26

What is the clinical sensitivity of SMN1 deletion/copy number analysis to diagnose spinal muscular atrophy (SMA) in Caucasians? A. >99% B. 95% C. 80% D. 60% E. 40% F. 20%

Answer 26

B. 95%

Question 27

Which one of the following populations will have the lowest detection rate if an assay for exon 7 of SMN1 deletion/copy-number analysis is used to identify carriers of spinal muscular atrophy (SMA)? A. African American B. Ashkenazi Jewish C. Asian D. Caucasian E. Hispanic

Answer 27

A. African American 71% in AA

Question 28

 Which one of the following statements regarding spinal muscular atrophy (SMA) is NOT true? A. The posterior residual risk for a Caucasian with no family history of SMA to be a carrier following the identification of two copies of SMN1 exon 7 is higher than that of an African American. B. The posterior residual risk for a Caucasian with no family history of SMA to be a carrier following the identification of two copies of SMN1 exon 7 is higher than in a Caucasian with three copies of SMN1 exon 7. C. The posterior residual risk for a Caucasian with no family history of SMA to be a carrier following the identification of two copies of SMN1 exon 7 is higher than that of an African American with three copies of SMN1 exon 7. D. None of the above.

Answer 28

A. The posterior residual risk for a Caucasian with no family history of SMA to be a carrier following the identification of two copies of SMN1 exon 7 is higher than that of an African American.

Question 29

A scientist in a clinical molecular genetic laboratory plans to validate a quantitative polymerase chain reaction (PCR) assay for spinal muscular atrophy (SMA). Which one of the following designs for the assay should NOT be used? A. Monitoring the efficiency of PCR amplification of the internal standard reference gene relative to the SMN1 gene. B. Checking the consistency of the copy number of genomic internal standard reference gene within the genome. C. Using two independent copy-number internal standard reference genes. D. Using sequencing analysis as a reflex study to rule out the presence of subtle intragenic point variants within the SMN1 gene. E. Using exon 8 as the internal control to test the copy number of SMN1.

Answer 29

E. Using exon 8 as the internal control to test the copy number of SMN1.

Question 30

How frequently is ALS familial? A. <1% B. 5%–10% C. 20%–30% D. 50% E. 70%–80% F. 90%

Answer 30

B. 5%–10% Autosomal dominant > AR or X-linked

Question 31

Which one of the following molecular assays would be the most appropriate to confirm the diagnosis of ALS? A. Exome sequencing analysis B. Multiplex ligation-dependent probe amplification (MLPA) C. Next-generation sequencing analysis D. Quantitative PCR analysis E. Restriction-fragment–length polymorphism analysis F. Sanger sequencing analysis G. None of the above

Answer 31

C. Next-generation sequencing analysis SOD1 20% of familial ALS, 3% sporadic ALS 15 different loci for ALS

Question 32

A pathogenic variant, c.112G>A(p.Gly37Arg), in the SOD1 gene was detected. The patient asked the physician if his 20-year-old asymptomatic daughter might be tested. Which one of the following would be the most appropriate response to the request from the patient? A. Referring the patient’s daughter to a pediatric clinic B. Refusing to test the patient’s daughter since she did not have symptoms C. Refusing to test the patient’s daughter since insurance would not pay for testing for asymptomatic individuals D. Testing the patient’s daughter for the familial pathogenic variant after obtaining informed consent E. None of the above

Answer 32

D. Testing the patient’s daughter for the familial pathogenic variant after obtaining informed consent

Question 33

A pathogenic variant, c.112G>A(p.Gly37Arg), in the SOD1 gene was detected. The patient asked the physician if her 16-year-old asymptomatic daughter might be tested. Which one of the following would be the most appropriate response to the request from the patient? A. Referring the patient’s daughter to a pediatric clinic B. Refusing to test the patient’s daughter since she did not have symptoms C. Refusing to test the patient’s daughter since insurance would not pay for testing for asymptomatic individuals D. Testing the patient’s daughter for the familial pathogenic variant after obtaining informed consent E. None of the above

Answer 33

B. Refusing to test the patient’s daughter since she did not have symptoms Testing children for adult-onset disorders may be inappropriate

Question 34

51 yo man presented for bilaterial tibialis weakness, scapular winging, difficulty raising his arms above his head, a crooked smile and myopathic EMG findings. Facioscapulohumeral muscular dystrophy (FMD) was suspected and molecular genetic testing confirmed the diagnosis. Which one of the following types of variants would the patient most likely have? A. Copy-number variants B. Macrosatellite variants C. Microsatellite variants D. Single-nucleotide variants E. None of the above

Answer 34

B. Macrosatellite variants DUX4 double homeobox containing gene lies in the macrosatellite repeat D4Z4 on chromosome 4q35, which has a length between 11 and 100 repeat units on normal alleles. FSHD2 - rare SMCHD1 - methylation and alteration of DUX4 expression

Question 35

The patient was diagnosed with muscular dystrophy, probably facioscapulohumeral muscular dystrophy (FMD). A molecular genetic testing confirmed the diagnosis. Which one of the following assays was most likely used for the molecular genetic testing? A. Exome sequencing analysis B. Multiplex ligation-dependent probe amplification (MLPA) C. Next-generation sequencing analysis D. Quantitative PCR analysis E. Sanger sequencing analysis F. Southern blot G. None of the above

Answer 35

F. Southern blot

Question 36

Patient presents with hemiatrophy without organ dysymmetry. The patient was diagnosed with muscular dystrophy, probably facioscapulohumeral muscular dystrophy (FMD). A molecular genetic testing confirmed the diagnosis. Which one of the following pathogenic variants would the patient most likely have? A. c.2068C>T(p.Pro690Ser) in the SMCHD1 gene B. 33- and 48-kb alleles for D4Z4 using EcoRI and the p13E-11 probe for Southern blot C. 44- and 52-kb alleles for D4Z4 using EcoRI and the p13E-11 probe for Southern blot D. A t(4;19)(q35;13) involving DUX4 at 4q35 E. None of the above

Answer 36

B. 33- and 48-kb alleles for D4Z4 using EcoRI and the p13E-11 probe for Southern blot In general, contractions of the D4Z4 allele in the 4A haplotype causes facioscapulohumeral muscular dystrophy 1 (FSHD1) because it is permissive to DUX4 expression. The normal D4Z4A allele has between 11 and 100 units of the 3.3-kb repeat sequence (fragments of 43 kb or greater using EcoRI and the p13E-11 probe). Borderline alleles are defined by a D4Z4 locus with 10 or 11 repeat units (35–40 kb).

Question 37

An electromyography/nerve-conduction study showed diffuse irritable myopathic process consistent with muscle dystrophy. A muscle biopsy from the left biceps showed findings consistent with glycogen storage disease type II. A molecular genetic testing confirmed the diagnosis. Which one of the following genes most likely harbored the pathogenic variants? A. GAA B. GBA C. HEXA D. SMPD1 E. None of the above

Answer 37

A. GAA acid alpha glucosidase GSD type II

Question 38

Pompe disease, and a molecular genetics study confirmed the diagnosis. Which one of the following assays was most likely used for the molecular genetics testing? A. Exome sequencing analysis B. Multiplex ligation-dependent probe amplification (MLPA) C. Next-generation sequencing analysis D. Quantitative PCR analysis E. Sanger sequencing analysis F. Southern blot G. None of the above

Answer 38

E. Sanger sequencing analysis 150 pathogenic variants in GAA Sequencing analysis detects 83%–93% of pathogenic variants in probands. Gene-targeted deletion/duplication analysis detects 5%–13% of pathogenic variants in probands. An estimated 50%–60% of African American patients have the pathogenic variant p.Arg854Ter. An estimated 40%–80% of Chinese patients have the pathogenic variant p.Asp645Glu. An estimated 50%–85% of adult patients have the pathogenic variant c.336-13T>G,

Question 39

The sequencing analysis for a baby boy detected a homozygous variant, c.1726G>A(p.Gly576Ser) in the GAA gene. Which one of the following would be the most appropriate interpretation of these findings? A. The patient had infantile-onset Pompe disease. B. The patient had late-onset Pompe disease. C. The patient did not have Pompe disease. D. The patient’s results raised concern for a partial or a full deletion of GAA. E. The patient’s results raised concern for a variant in the primer region.

Answer 39

C. The patient did not have Pompe disease. pseudodeficiency allele c.1726G>A (p.Gly576Ser), which is relatively common in Asian populations,

Question 40

What is the disorder? 1yo AJ boy with febrile episodes, weight loss, neuropathy, poor muscular tone, diminished lacrimation, vomiting attacks and neuropsychomotor retardation. A. Familial dysautonomia B. Hereditary neuropathy with liability to pressure palsies (HNLPP) C. Smith–Lemli–Opitz syndrome D. Smith–Magenis syndrome E. None of the above

Answer 40

A. Familial dysautonomia

Question 41

What is the disorder? 1yo AJ boy with febrile episodes, weight loss, neuropathy, poor muscular tone, diminished lacrimation, vomiting attacks and neuropsychomotor retardation. A. Canavan disease B. Familial dysautonomia C. Gaucher disease D. Pompe disease E. None of the above

Answer 41

B. Familial dysautonomia Riley–Day syndrome, autosomal recessive

Question 42

What is the recurrent risk for another child with familial dysautonomia? A. 3/4 B. 2/3 C. 1/2 D. 1/4 E. Increase to up to 1% F. Unpredictable

Answer 42

D. 1/4 A single pathogenic variant in intron 20 of the IKBKAP gene (2507+6T→C) accounts for >99% of the mutations in the Ashkenazi Jewish population. ELP1 - elongator complex protein 1 IkappaB Kinase Complex-Associated Protein

Question 43

Familial dysautonomia, what would be the next step to confirm the diagnosis? A. Chromosomal microarray analysis B. Next-generation sequencing C. Sanger sequencing D. Targeted-mutation analysis E. Whole-exome sequencing F. None of the above

Answer 43

D. Targeted-mutation analysis

Question 44

Familial dysautonomia, where would the pathogenic variant most likely be located? A. Promoter B. 5′ UTR C. Exon D. Intron E. Splice site F. 3′ UTR

Answer 44

D. Intron intron 20 of the IKBKAP gene (c.2507+6T>C) accounts for >99% of the mutations in the Ashkenazi Jewish population. A second variant, c.2087G>C(p.Arg696Pro), is included in most carrier screening panels and accounts for the remainder of Ashkenazi Jewish pathogenic