|LETTER TO THE EDITOR
|Year : 2014 | Volume
| Issue : 2 | Page : 142-143
Congenital myasthenic syndrome: A common disease; in rare age group
Nagarjunakonda Venkata Sundarachari1, Amalakanti Sridhar2, Blessy Manohar2
1 Department of Neurology, Guntur Medical College, Guntur, Andhra Pradesh, India
2 Department of General Medicine, Guntur Medical College, Guntur, Andhra Pradesh, India
|Date of Web Publication||20-Jun-2014|
FF-5 PG Hostel, Government General Hospital, Guntur - 522 001, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Sundarachari NV, Sridhar A, Manohar B. Congenital myasthenic syndrome: A common disease; in rare age group. J NTR Univ Health Sci 2014;3:142-3
|How to cite this URL:|
Sundarachari NV, Sridhar A, Manohar B. Congenital myasthenic syndrome: A common disease; in rare age group. J NTR Univ Health Sci [serial online] 2014 [cited 2020 Jan 18];3:142-3. Available from: http://www.jdrntruhs.org/text.asp?2014/3/2/142/134897
Congenital myasthenic syndromes (CMS) are characterized by varying degrees of muscle weakness due to impaired neuromuscular transmission and are classified into presynaptic, synaptic basal lamina-associated and postsynaptic sub groups.  They are recognized only by a well-informed physician or a neurologist and are treatable conditions. They are seen in the early first decade of life. Some of them may present in adults also.  About 4% of myasthenic patients have a congenital cause with the typical age of presentation being 3 years. We present a case with a later age of presentation.
A 12-year-old boy noticed that his eyes were big in the morning and becoming small as the day progress. He also had difficulty in chewing hard food stuffs, and in blowing a whistle. He could not watch TV for a long time. He had difficulty in writing for a prolonged time and could not carry his school bag. Since 5 years the boy noticed difficulty in climbing upstairs. On questioning his parents revealed that the eyes of their son were small but, they did not make out any diurnal variation at that time. Their marriage was not consanguineous. There was no delay in attaining motor milestones.
On examination bilateral weakness of extra ocular and facial muscles was present. Quadriparesis was noted, with proximal muscle weakness predominance.
Serum acetylcholine receptor (AChR) antibodies were within normal limits (0.2 nmol/l). Thyroid profile was normal, creatine phosphokinase (CPK) MB levels were normal. Computed tomography chest showed no abnormality. Neostigmine test was positive. There was significant decremental response in the repetitive nerve stimulation (RNS) test (V th amplitude = −16%).
The characteristic fatigability and the decremental response in the RNS test in our patient pointed toward a neuromuscular disorder. The presentation was from childhood. The serum AChR antibodies, CPK MB and his thyroid profile were normal. Definitive diagnosis required intercostal muscle biopsy, receptor binding studies, acetylcholine content, in vitro electrophysiology for determination of miniature end plate potential amplitude and frequency and conductance and kinetics of individual channels. However, they could not be done due to technical and economical limitations. A clinical diagnosis of a congenital myasthenic syndrome could be made.
CMS were described as early as 1937 (Rothbart 1937) but received little attention until after the autoimmune origin of acquired myasthenia gravis was discovered in the 1970s. In the late 1970s and 1980s, distinct phenotypic features of a number of CMS were described (Engel et al. 1977; Engel et al. 1982; Engel and Lambert 1987; Mora et al. 1987), but their molecular basis remained unsolved until the 1990s. CMS caused by defects in each subunit of the AChR and in ColQ, choline acetyltransferase, rapsyn, Nav1.4, MuSK and Dok-7 have been identified. 
These disorders are distinguished by neonatal onset, fluctuating and sometimes progressive weakness that may be quite severe, sometimes pronounced muscle hypotrophy, persistent ptosis and seronegativity for anti-AChR and anti-MuSK antibodies. CMS are usually associated with a favorable prognosis if it occurs beyond neonatal period with early diagnosis and appropriate treatment. Our case is a typical example.
The disease was noticed by the patient due its progression in the recent period. The cause for this progression is yet to be elucidated. Such progressive disorders have rarely been reported. It is therefore imperative that further studies for identification of variants of the disease are to be taken up and clinicians should be sensitized about these presentations.
| Acknowledgments|| |
The author would like to thank Department of Radiology, Government General Hospital, Guntur.
| References|| |
|1.||Hantaï D, Richard P, Koenig J, Eymard B. Congenital myasthenic syndromes. Curr Opin Neurol 2004;17:539-51. |
|2.||Khwaja GA, Chowdhury D, Gupta M. Congenital myasthenic syndrome: Report of four cases and brief review of literature. Neurol India 2000;48:266-71. |
|3.||Engel AG, Shen XM, Selcen D, Sine SM. What have we learned from the congenital myasthenic syndromes. J Mol Neurosci 2010;40:143-53. |