Relationship between the occurrence of benign fasciculations, patient‘s psychological profile, bio­chemical parameters, and mutations in the SMN1 gene

Summary

Benign fasciculations, in their chronic form as benign fasciculation syndrome, can be attributed to a range of causes from metabolic-endocrine factors to psychological instability with manifestations of anxiety and depression. The association with potential mutations in the SMN1 gene has not been extensively investigated to date. The study included 34 patients with chronic fasciculation syndrome, 21 men and 13 women, who underwent EMG and in whom neuromuscular disease was excluded. Biochemical blood tests were performed and DNA was examined for possible mutation in the SMN1 gene, and a basic psychological profile of the patient was determined by psychological examination. Values of fundamental biochemical parameters, including ions (Na, Cl, K, Mg, Ca), as well as muscle enzymes, thyroid hormones, parathormone, calcitonin, and cortisol, and antibodies against Lyme disease did not exhibit significant deviations from typical population values. Psychological assessments revealed that 21 out of 22 probands (95.5%) who agreed to psychological evaluation displayed increased anxiety or depressive syndrome. The expected deletion in the SMN1 gene was not detected in any of the 34 probands.

Keywords:

anxiety – Mutation – Hormones – Caffeine – biomarkers – SMN1 gene – fasciculation

Introduction

In the literature, it is noted that fasciculations can arise from various causes, ranging from metabolic-endocrine factors to adverse effects of drugs, and even to serious neurological diseases such as Amyotrophic lateral sclerosis (ALS), thus motor neuron disease, neuropathies, and root syndromes. Their occurrence is often attributed to increased neuromuscular irritability due to excessive consumption of stimulants (caffeine, theine) or chronic anxiety. If the condition persists, and neurological disease is ruled out as the cause of fasciculations, the finding can be labelled as Benign fasciculation syndrome (BFS), which generally has a good prognosis [1,2]. There are studies that have described an association between BFS and psychological difficulties, especially anxiety [3,4]. However, the literature has not yet addressed the relationship between fasciculations and the presence of heterozygous deletions in the SMN1 (survival of motor neuron) gene. Homozygous deletions of exons 7 and 8 of the SMN1 gene result in spinal muscular atrophy, one of the symptoms of which is a typical neurogenic finding in EMG and the presence of fasciculations in both clinical and EMG examinations. The frequency of heterozygous carriers of SMN1 gene deletions in the population is approximately 1 : 50 [5]. It can be assumed that mutation carriers may experience (sub)clinical symptoms such as weakness, elevated muscle enzymes, needle EMG findings, and fasciculations, as signs of insignificant motor neuron lesions. However, there is currently no comprehensive work supported by extensive data available in the literature that deals with the frequency of metabolic and endocrine causes of BFS and especially with eventual proportion of deletions, in particular, the contribution of deletions or point mutations in the SMN1 gene. The aim of this project was to determine the relationship between the occurrence of benign fasciculations, biochemical parameters, psychosocial factors, and the presence of deletions in the SMN1 gene.

Materials and methods

The study included patients who underwent EMG examination for the presence of fasciculations, mostly with a concern of excluding ALS or other neuromuscular diseases. All of them had sensations of muscle twitching, mostly in the calves or thighs of the lower limbs, less often in the small hand muscles or in the arms or face. All had difficulties lasting weeks to months, sometimes recurring over a longer period.

 Patients were examined clinically and electromyographically. EMG examined several nerves and at least two muscles, recording both- resting muscle activity and voluntary recruitment curve (turns-amplitude analysis) and a complete analysis of motor unit potentials in the most affected subjective muscles and distal muscles (e.g., tibialis anterior, abductor digiti minimi, abductor pollicis brevis, etc.). Detailed medical history was recorded, including pharmacological and possible use of stimulants (caffeine, theine, or drugs), as well as responses to questions regarding the extent of stress and sleep disturbances. After ruling out motor unit remodeling in the EMG findings and excluding neuromuscular disease, patients were informed about the ongoing study and signed consent for participation in the study and further examinations. Subsequently, the examination included the levels of muscle enzymes (aspartate aminotransferase - AST, myoglobin, creatine kinase - CK, lactate dehydrogenase), alanine aminotransferase – AST, ions, thyroid hormones (T4, TSH), parathyroid hormone, cortisol, procalcitonin, vitamin D levels, and antibodies against Lyme disease (IgM, IgG). With patient consent, a basic psychological profile and stress factors were determined through psychological evaluation. The MLPA method using the SALSA Probemix P021/P060 kit and subsequent analysis on the ABI 3130 genetic analyzer were used to examine the number of copies of exons 7 and 8 of the SMN1 and SMN2 genes [6]. Patients were clinically and EMG re-evaluated 6–18 months later, and neuromuscular disease was again ruled out, confirming BFS. Statistical analysis evaluated basic demographic data (gender, age), measured biochemical parameters, and reported values as means and standard deviations (SD), or percentages (for stimulants, psychological abnormalities).

Results

A total of 34 patients were included in the study from 2020 to 2023 years, consisting of 21 males and 13 females. All had documented fasciculations on EMG, muscle remodeling was excluded, and thus neuromuscular disease. The findings were evaluated as benign fasciculation syndrome. The average age of patients was 39.4 ± 9.7 years (age range 18–57 years), 39.6 ± 10.2 years for males and 39.2 ± 8.7 years for females. Twenty-nine patients had normal values of muscle enzymes (CK, AST, myoglobin), while 5 patients had slightly elevated CK values. The average CK value for the entire group was 2.0 ± 0.9 µkat/l, with a range of 0.9–4.2. The measured AST values were 0.41 ± 0.08 µkat/L, myoglobin 31.22 ± 11.25 µg/L, all within the normal range.

Other biochemical values were mostly within the normal range (ions - Na, Cl, K, Mg, Ca, ALT, free T4, TSH). No patient had elevated levels of antibodies against Lyme disease. In 29 probands the 25-OH value of vitamin D was obtained, in 17 of them it was below the normal range of values and in 12 within the normal range, the average value in all of them was 69.24 ± 23.08 (in values 25–115) nmol/L. The measured values of parathyroid hormone were 3.35 ± 1.69 pmol/L, 3 times outside the norm; calcitonin 2.68 ± 2.90 ng/L (norm 0–11.8), 1 time outside the norm. Myoglobin 31.14 ± 11.41 µg/L, cortisol 296.83 ± 157.37 nmol/L, here measured value 3 times just exceeded the upper limit of the norm.

23 patients (67.6%) reported regular use of stimulants, exclusively caffeine and theine, with an average daily intake of 2.7 cups of coffee or tea.

Psychological examination revealed increased anxiety or depressive syndrome, or heightened experience of somatic difficulties in 21 out of 22 (also 95.5%) probands who consented to psychological examination (Tabel 1). Sleep disturbances were reported by 10 probands, all of whom had some of the mentioned psychological abnormalities.

Genetic testing (demonstrated by MLPA method) showed that none of the examined patients (23 patients) had deletions in exons 7 and 8 of the SMN1 gene.

Table 1. Measured values ​​of biochemical and biological parameters.

AST – aspartate aminotransferase; CK – creatine kinase

Discussion

The study demonstrated that in our patient cohort BFS occurs in people of younger and middle age, with an average of 39.4 ± 9.7 years, more frequently in males than females, in a ratio of 21 : 13 (approximately 1.5 : 1). Notably, normal values of basic biochemical parameters - ions (Na, Cl, K, Mg, Ca) and enzymes typically associated with muscle diseases (AST, ALT, myoglobin, and CK) were observed. While CK levels were mildly elevated in 5 cases, the average CK level for the entire group was 2.0 ± 0.9 µkat/L, mostly remaining within the normative values.  

The slight elevation in individual cases can also be attributed to the fact that the biochemical values were collected in the hour following the needle EMG. Also, using the EFNS recommendation for cut-off values as 1.5 times the upper limit of normal [7,8], the respective values cannot be assessed as hyperCKemia. Original papers investigating the relationship between creatine kinase levels and benign fasciculation syndrome or the occurrence of fasciculations are not available. In this respect, our work is of value because it demonstrates that benign fasciculations are not associated with CK elevation, or only at very low levels, which contrasts with the hyperCKemia commonly found in neuromuscular diseases [9–11].

Interestingly, the study also found low levels of vitamin D (average 69.24 ± 23.08 nmol/L), which were significantly below the minimum normative, despite some patients taking vitamin D orally. Given the lack of a control group matched for gender, age, season, and lifestyle, it is difficult to draw a definitive conclusion, especially when low vitamin D levels in the (European) population have been reported in numerous studies [12–14]. There is room for expanding the study to a larger population for more conclusive results, although this would be operationally challenging.

Efforts to demonstrate the effects of other hormones affecting calcium metabolism (parathyroid hormone, calcitonin) did not yield significant findings. Similarly, there was no association found between BFS and thyroid hormone levels (T4, TSH), cortisol, procalcitonin, or Lyme disease antibodies.

A significant finding in the study was the presence of psychological instability (in 21 out of 22 examined individuals), often accompanied by sleep disturbances and the use of caffeine and theine. However, it is challenging to statistically evaluate the significance and differentiation from the general population (matched for age and gender) due to the absence of data on the general population. Nevertheless, this finding is consistent with a body of literature that confirms the presence of these psychological findings in BFS patients, somatization of psychological difficulties, and the necessity of comprehensive treatment with antidepressants and psychotherapy (cognitive-behavioral therapy) [4,15].

Conclusion

The study demonstrated that the occurrence of fasciculations, evaluated as benign fasciculation syndrome, is not associated with deletions in the SMN1 gene, abnormalities in biochemical parameters (Na, Cl, K, Mg, Ca), or “muscle” enzymes (CK, myoglobin, AST). The study did not find an association with Lyme disease (negative antibodies against Lyme disease). There was also no association between BFS and abnormalities in thyroid hormone levels (T4, TSH), parathyroid hormone, cortisol, or procalcitonin.  

The study showed a remarkably frequent (21 out of 22 examined) occurrence of psychological problems in patients with BFS (increased anxiety, depressive syndrome, possibly increased experience of somatic difficulties).

In conclusion, based on the study results, it is recommended for future research to expand into a prospective longitudinal study focused on monitoring the relationship between psychological status, the intensity of somatic difficulties, the occurrence of fasciculations, and the response to potential pharmacological or psychotherapeutic treatment of anxiety and depression.

Ethical aspects

The study was approved by the local ethics committee at IKEM and TN with multicentric competence on 8 April 2020, No. 8622/1.4.2020 (G-20-10).

Financial Support

Supported by the program project of the Ministry of Health of the Czech Republic RVO – TN, 00064190.

Conflict of Interest

The author declares that he has no commercial interests related to the subject of the study.