Skip to main content Accessibility help
×
Home
Hostname: page-component-5d6d958fb5-mhr6q Total loading time: 0.913 Render date: 2022-11-28T05:17:38.682Z Has data issue: true Feature Flags: { "shouldUseShareProductTool": true, "shouldUseHypothesis": true, "isUnsiloEnabled": true, "useRatesEcommerce": false, "displayNetworkTab": true, "displayNetworkMapGraph": false, "useSa": true } hasContentIssue true

Nonlethal CHRNA1-Related Congenital Myasthenic Syndrome with a Homozygous Null Mutation

Published online by Cambridge University Press:  17 October 2016

Osorio Abath Neto
Affiliation:
Departamento de Neurologia, Faculdade de Medicina Universidade de São Paulo, São Paulo, Brazil
Carlos Otto Heise
Affiliation:
Departamento de Neurologia, Faculdade de Medicina Universidade de São Paulo, São Paulo, Brazil
Cristiane de Araújo Martins Moreno
Affiliation:
Departamento de Neurologia, Faculdade de Medicina Universidade de São Paulo, São Paulo, Brazil
Eduardo de Paula Estephan
Affiliation:
Departamento de Neurologia, Faculdade de Medicina Universidade de São Paulo, São Paulo, Brazil
Lilia Mesrob
Affiliation:
Centre National de Génotypage, Institut de GénomiqueEvry, France
Doris Lechner
Affiliation:
Centre National de Génotypage, Institut de GénomiqueEvry, France
Anne Boland
Affiliation:
Centre National de Génotypage, Institut de GénomiqueEvry, France
Jean-François Deleuze
Affiliation:
Centre National de Génotypage, Institut de GénomiqueEvry, France
Acary Souza Bulle Oliveira
Affiliation:
Setor de Doenças Neuromusculares, Departamento de Neurologia, Universidade Federal de São PauloSão Paulo, Brazil
Umbertina Conti Reed
Affiliation:
Departamento de Neurologia, Faculdade de Medicina Universidade de São Paulo, São Paulo, Brazil
Valérie Biancalana
Affiliation:
Faculté de Médecine, Laboratoire de Diagnostic GénétiqueNouvel Hopital Civil, Strasbourg, France
Jocelyn Laporte
Affiliation:
Department of Translational Medicine and Neurogenetics, IGBMC, INSERM U964, CNRS UMR7104University of Strasbourg, Collège de France, Illkirch, France
Edmar Zanoteli*
Affiliation:
Departamento de Neurologia Faculdade de Medicina, Universidade de São PauloAvenida Dr. Enéas de Carvalho Aguiar 2555 andar, sala 5131, Cerqueira Cesar05403-900, Sao Paulo, Brazil
Rights & Permissions[Opens in a new window]

Abstract

Type
Letters to the Editor
Copyright
Copyright © The Canadian Journal of Neurological Sciences Inc. 2016 

Congenital myasthenic syndromes (CMSs) are a heterogeneous group of genetic disorders affecting components of the neuromuscular junction (NMJ).Reference Rodriguez Cruz, Palace and Beeson 1 , Reference Engel, Shen, Selcen and Sine 2 Postsynaptic NMJ defects encompass up to 75% of CMS cases and comprise mutations in genes that encode different subunits of the acetylcholine receptor (CHRNA1, CHRNB1, CHRND and CHRNE) or proteins important to maintain the structure or function of the NMJ, such as MUSK, RAPSN or DOK7.Reference Harper 3 Defects in the acetylcholine receptor (AChR) can be primary, resulting from a decreased expression of one of the subunits, or functionally subdivided into fast- (FCCMS) and slow-channel (SCCMS) congenital myasthenic syndromes.

Most cases of primary AChR deficiency involve mutations in the CHRNE gene, because the epsilon subunit can be substituted by the foetal gamma subunit, thus rescuing the phenotype. Compound heterozygous or homozygous null mutations in the CHRNA1, CHRNB or CHRND gene do not benefit from the gamma subunit rescue and are believed to be lethal. We herein present a nonlethal case of a severely affected CMS patient with a CHRNA1 homozygous null mutation.

We describe a boy who was referred to our neuromuscular disorders outpatient clinic at the age of 6 years for evaluation with a diagnosis of severe congenital myopathy. He was born from unaffected first-degree cousins of mixed ancestry (Portuguese, African and native) out of an uneventful pregnancy with reduced foetal movements. The couple had a previous pregnancy of twins with foetal demise at 7 months. Immediately after caesarean section, the patient required orotracheal intubation due to respiratory insufficiency and was admitted to the neonatal ICU, where he stayed for a year and a half. He was discharged to continue home care with gastrostomy and tracheostomy, requiring continuous BiPAP support. Despite having gradually improved, he remained severely impaired, never having acquired head control or the ability to sit. At our first evaluation, he was able to move his arms and legs on a plane, with proximal greater than distal weakness in all four limbs. Physical exam demonstrated bilateral ptosis with complete ophthalmoplegia, absence of facial expression, high-arched palate and marked hypotonia without contractures (Figure 1A). His serum CK level has always remained within the normal range. Muscle biopsy performed at 10 months by another service in the deltoid muscle showed marked predominance and atrophy of type 2 fibres without disruptions of the intermyofibrillar network (Figure 1B).

Figure 1 Main features of the case. (A) Facial aspects included marked ptosis and facial weakness, in addition to a prominent forehead and temporalis atrophy. Respiratory support via tracheostomy can also be seen. (B) Muscle biopsy shows marked predominance and atrophy of type 2 fibres (ATPase 9.4, white bar=50 μm). (C,D,E) NGS data alignment (Integrated Genome Viewer software) showing the mutation p.Gly466Arg in a homozygous state in the proband (C), and in a heterozygous state in the father (D) and mother (E). Coverages were 75, 92 and 129 reads, respectively.

We opted for direct exome sequencing to reach a final molecular diagnosis. Analysis of sequencing data of the trio consisted of filtering variants for known genes implicated in neuromuscular diseases, discarding variants with a minimum allele frequency (MAF) >0.5% in different population variant frequency databases (EVS, ExAC) or with a low pathogenicity prediction score combining evaluations of the PolyPhen-2 and SIFT tools. No variants survived the filtering pipeline for the X-linked and de novo analysis scenarios. Compound heterozygous variants were identified fitting the segregation, but they occurred in genes unrelated to the phenotype of the patient (SYNE1 and SYNE2). BAM files were thoroughly checked for coverage of known genes. In the homozygous recessive analysis scenario, we found the variant c.1396G>A (p.Gly466Arg), in exon 10 of the CHRNA1 gene (NM_001039523) (Figure 1D–F). It has been previously implicated in primary AChR-deficiency CMS.Reference Rahman, Masuda, Ohe, Ito, Hutchinson, Mayeda and Engel 4

A nerve conduction study was performed to demonstrate the NMJ impairment. Repetitive nerve stimulation of the ulnar and peroneal nerves, with recording in the abductor digiti minimi and tibialis anterior muscles, respectively, showed marked decrement of >70% in both the upper and lower limbs (Figure 2A,B). Concentric needle electromyography revealed instability of motor unit action potentials with increased jitter on voluntary contraction. The patient was then started on pyridostigmine and had an almost immediate improvement in limb movement, being able to raise his arms and legs against gravity, and gradual improvement in ventilatory function, reducing BiPAP support to the point where it was only necessary at night.

Figure 2 3-Hz repetitive stimulation test on the left ulnar nerve (A) and on the left peroneal nerve (B) showing a decrement greater than 70%.

The variant p.Gly466Arg gives rise to a primary AChR defect by way of reducing the expression of the AChR alpha subunit to a level of around 15% of normal.Reference Rahman, Masuda, Ohe, Ito, Hutchinson, Mayeda and Engel 4 It was previously described in a 53-year-old man with myasthenic symptoms since birth who harboured the mutation (under a different notation, it was referred to as p.Gly421Arg) in a heterozygous state, compounded with an additional heterozygous splicing disrupting mutation. He had partial response to pyridostigmine and amifampridine.

The patient we describe expands our understanding of the complex genetic picture of congenital myasthenic syndromes with the demonstration of a homozygous null mutation expected to give rise to a lethal phenotype but instead originating a severely affected progeny of asymptomatic carriers. The delay in diagnosis of a condition that benefits from immediate symptomatic treatment prompts one to emphasize the need to always consider a CMS diagnosis in severely hypotonic infants, even in patients with mild inconclusive muscle biopsies or suggestive of other diseases.Reference Kinali, Beeson, Pitt, Jungbluth, Simonds and Aloysius 5 In particular, type 2 fibre predominance or atrophy is not a common feature in CMS.Reference Kinali, Beeson, Pitt, Jungbluth, Simonds and Aloysius 5 Repetitive nerve stimulation may point to the diagnosis, and this is an important ancillary exam to order in these cases. On the other hand, the absence of decrement on repetitive nerve stimulation does not rule out NMJ defects. Single-fibre electromyography can be a technical challenge in young children, and normative values are not well defined.Reference Kosac, Gavillet and Whittacker 6 Molecular diagnosis and knowledge of the mutation effect in CMS is important to enable defining an effective and safe symptomatic treatment. Primary AChR deficiency and FCCMS may respond to pyridostigmine and amifampridine, cholinergic agents that must be avoided in SCCMS and in deficiency of Dok-7.Reference Engel, Shen, Selcen and Sine 2 Ideally, the choice of treatment should be withheld until a genetic diagnosis is reached, or done with close observation in a monitored setting.Reference Engel, Shen, Selcen and Sine 2 Of note, there are reports of NMJ involvement and myasthenic symptoms with response to acetylcholinesterase inhibitors in different forms of confirmed or nonspecific congenital myopathies,Reference Rodriguez Cruz, Sewry, Beeson, Jayawant, Squier and McWilliam 7 , Reference Robb, Sewry, Dowling, Feng, Cullup, Lillis and Abbs 8 an important differential diagnosis of CMS. Our present report illustrates how personalized genomics can quickly lead to personalized treatment in nonspecific cases.

ACKNOWLEDGMENTS

OAN was supported by a fellowship from the CAPES Foundation, Ministry of Education of Brazil (process no. 1286/51-2). This work was supported by grants from Fondation Maladies Rares to JL, as well as by the France Génomique National infrastructure, funded as part of the “Investissements d’Avenir” program managed by the Agence Nationale pour la Recherche (contract no. ANR-10-INBS-09).

DISCLOSURES

Osorio Abath Neto has the following disclosure: CAPES: researcher, grant.

Jocelyn Laporte has the following disclosures: FMR (Fondation Recherche Medicale): researcher, grant; ANR–FGN: researcher, grant.

Carlos Otto Heise, Cristiane de Araújo Martins Moreno, Eduardo de Paula Estephan, Lilia Mesrob, Doris Lechner, Anne Boland, Jean-François Deleuze, Acary Souza Bulle Oliveira, Umbertina Conti Reed, Valérie Biancalana and Edmar Zanoteli do not have anything to disclose.

STATEMENT OF AUTHORSHIP

OAN and EZ were responsible for the clinical description and follow-up of the patient, as well as for preparation of the first drafts of the manuscript. CAMM, EPE and UCR helped in the clinical description and follow-up of the patient. COH performed nerve conduction studies and helped discuss the electrophysiological findings. ASBO was responsible for the muscle biopsy of the patient and its report. LM, DL, AB and JFD performed exome sequencing. VB and JL helped in the analysis of the exome data. OAN, EZ and JL reviewed and prepared the final version of the manuscript.

References

REFERENCES

1. Rodriguez Cruz, PM, Palace, J, Beeson, D. Inherited disorders of the neuromuscular junction: an update. J Neurol. 2014;261(11):2234-2243. Epub ahead of print Oct 11.CrossRefGoogle ScholarPubMed
2. Engel, AG, Shen, XM, Selcen, D, Sine, SM. Congenital myasthenic syndromes: pathogenesis, diagnosis, and treatment. Lancet Neurol. 2015;14(5):420-434. Epub ahead of print Mar 26.CrossRefGoogle Scholar
3. Harper, CM. Congenital myasthenic syndromes. Semin Neurol. 2004;24(1):111-123.CrossRefGoogle ScholarPubMed
4. Rahman, MA, Masuda, A, Ohe, K, Ito, M, Hutchinson, DO, Mayeda, A, Engel, AG, et al. HnRNP L and hnRNP LL antagonistically modulate PTB-mediated splicing suppression of CHRNA1 pre-mRNA. Sci Rep. 2013;3:2931. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3796306/.CrossRefGoogle ScholarPubMed
5. Kinali, M, Beeson, D, Pitt, MC, Jungbluth, H, Simonds, AK, Aloysius, A, et al. Congenital myasthenic syndromes in childhood: diagnostic and management challenges. J Neuroimmunol. 2008;201–202:6-12; Epub ahead of print Aug 15.CrossRefGoogle Scholar
6. Kosac, A, Gavillet, E, Whittacker, RG. Neurophysiological testing in congenital myasthenic syndromes: a systematic review of published normal data. Muscle Nerve. 2013;48(5):711-715.CrossRefGoogle Scholar
7. Rodriguez Cruz, PM, Sewry, C, Beeson, D, Jayawant, S, Squier, W, McWilliam, R, et al. Congenital myopathies with secondary neuromuscular transmission defects; a case report and review of the literature. Neuromuscul Disord. 2014;24(12):1103-1110. Epub ahead of print Jul 30.CrossRefGoogle ScholarPubMed
8. Robb, SA, Sewry, CA, Dowling, JJ, Feng, L, Cullup, T, Lillis, S, Abbs, S, et al. Impaired neuromuscular transmission and response to acetylcholinesterase inhibitors in centronuclear myopathies. Neuromuscul Disord. 2011;21(6):379-386. Epub ahead of print Mar 25.CrossRefGoogle Scholar
Figure 0

Figure 1 Main features of the case. (A) Facial aspects included marked ptosis and facial weakness, in addition to a prominent forehead and temporalis atrophy. Respiratory support via tracheostomy can also be seen. (B) Muscle biopsy shows marked predominance and atrophy of type 2 fibres (ATPase 9.4, white bar=50 μm). (C,D,E) NGS data alignment (Integrated Genome Viewer software) showing the mutation p.Gly466Arg in a homozygous state in the proband (C), and in a heterozygous state in the father (D) and mother (E). Coverages were 75, 92 and 129 reads, respectively.

Figure 1

Figure 2 3-Hz repetitive stimulation test on the left ulnar nerve (A) and on the left peroneal nerve (B) showing a decrement greater than 70%.

You have Access
7
Cited by

Save article to Kindle

To save this article to your Kindle, first ensure coreplatform@cambridge.org is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.

Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Nonlethal CHRNA1-Related Congenital Myasthenic Syndrome with a Homozygous Null Mutation
Available formats
×

Save article to Dropbox

To save this article to your Dropbox account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Dropbox account. Find out more about saving content to Dropbox.

Nonlethal CHRNA1-Related Congenital Myasthenic Syndrome with a Homozygous Null Mutation
Available formats
×

Save article to Google Drive

To save this article to your Google Drive account, please select one or more formats and confirm that you agree to abide by our usage policies. If this is the first time you used this feature, you will be asked to authorise Cambridge Core to connect with your Google Drive account. Find out more about saving content to Google Drive.

Nonlethal CHRNA1-Related Congenital Myasthenic Syndrome with a Homozygous Null Mutation
Available formats
×
×

Reply to: Submit a response

Please enter your response.

Your details

Please enter a valid email address.

Conflicting interests

Do you have any conflicting interests? *