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Table 1 Summary of the clinical, neurophysiological, and therapeutic features of CMS cases with SLC25A1 pathogenic variants

From: A case report of an intermediate phenotype between congenital myasthenic syndrome and D-2- and L-2-hydroxyglutaric aciduria due to novel SLC25A1 variants

 

Reference [5]

Reference [6]

Reference [7]

Our case

Number of the patients

2

4

9

1

Ethnicity

English

Two Indian; one Greek Pomak; one Pakistani

Arabian

Chinese

Variants

R247Q

R247Q

R247Q in 6 pts.; D69Y in 3 pts

R210X; V49M

Zygosity

Homozygous

Homozygous

Homozygous

Compound heterozygous

Age at onset

Less than 2 years

Infancy

Infancy

9 months

CMS-associated features

Fatigability

Yes

Yes

Yes

Yes

Ocular involvement

Ptosis and/or diplopia

Ptosis and/or diplopia

Ptosis and/or diplopia

Ptosis and ophthalmoplegia

Cervical muscle weakness

Neck flexion weakness in one patient

Neck flexion weakness in one patient

No

No

Bulbar weakness

Dysarthria with fatigable speech in one patient

In 2 pts

Stridor in 2 pts.; No stridor in 5 pts.; ND in 2 pts

Yes, stridor and dysarthria

Limb muscle weakness

Yes, proximal

Yes, proximal

Yes, proximal

Yes, proximal

Facial involvement

In one patient

ND

ND

Yes, chewing weakness

Myasthenic crises

No

No

No

Yes, twice

RNS on 3 Hz stimulation

Negative in one patient; ND in one patient

Positive in 2 pts.;

Negative in 2 pts

Positive in one patient; Negative in 5 pts.; ND in 3 pts

Positive

Abnormal jitter with block

Positive in one patient; ND in one patient

Negative in one patient;

ND in 3 pts

ND

ND

Other features

Hypotonia

No

Hypermobility in two pts

No

Yes

Epilepsy

No

No

No

Yes

Intellectual disability

Mild

Mild

Mild ID in 2 pts.; No ID in 3 pts.; ND in 2 pts.; NA in 2 pts

Mild

Urinary organic acids

Normal

Normal in one patient;

ND in 3 pts

Normal in 2 pts.; ND in 7 pts

Mild elevation of 2-oxoglutaric acid and lactate

Blood lactate levels

Normal

Elevation after exercise in 2 pts

Normal

Mild elevation

Muscle biopsy

Enlarged mitochondria and increased in number on EM in one patient;

ND in one patient

Fibre size variation, few central cores and sporadically accumulated mitochondria on EM in one patient; Mildly atrophic fibre, normal COX staining and mild reduction in complex 1 activity in one patient; ND in two pts.

Normal in one patient;

Non-specific results in one patient;

ND in 7 pts

Atrophy of type IIB muscle fibre with normal COX and SDH staining;

No changes in mitochondria on EM

Responsive to treatment

AChEI

Partial response in one patient; No response in one patient

Partial response in one patient;

No response in 3 pts

No response in 2 pts.;

ND in 7 pts

Yes, Partial

3,4-DAP

Good response in one patient;

ND in one patient

ND

ND

ND

Salbutamol

ND

No response in 2 pts.;

ND in 2 pts

ND

No

  1. Abbreviations: ND not determined, Pts patients, RNS repetitive nerve stimulation, ID intellectual disability, EM electron microscopy, AChEI acetylcholinesterase inhibitor, 3,4-DAP 3,4-diaminopyridine, COX cytochrome c oxidase, SDH succinate dehydrogenase, NA not applicable