High rate of autonomic neuropathy in Cornelia de Lange Syndrome

Background Cornelia de Lange Syndrome (CdLS) is a rare congenital disorder characterized by typical facial features, growth failure, limb abnormalities, and gastroesophageal dysfunction that may be caused by mutations in several genes that disrupt gene regulation early in development. Symptoms in individuals with CdLS suggest that the peripheral nervous system (PNS) is involved, yet there is little direct evidence. Method Somatic nervous system was evaluated by conventional motor and sensory nerve conduction studies and autonomic nervous system by heart rate variability, sympathetic skin response and sudomotor testing. CdLS Clinical Score and genetic studies were also obtained. Results Sympathetic skin response and sudomotor test were pathological in 35% and 34% of the individuals with CdLS, respectively. Nevertheless, normal values in large fiber nerve function studies. Conclusions Autonomic nervous system (ANS) dysfunction is found in many individuals with Cornelia de Lange Syndrome, and could be related to premature aging. Supplementary Information The online version contains supplementary material available at 10.1186/s13023-021-02082-y.

aged 7-48 years). All of the individuals with CdLS and controls were Caucasian, except 3 Latino and 1 Middle East subjects in the CdLS group. The protocol study was approved by the Ethics Committee of Clinical Research from the Government of Aragón (CEICA;PI16/225). All the individuals with CdLS and controls gave informed consent for their participation.
To evaluate the somatic peripheral nervous system, conventional motor and sensory nerve conduction studies [11][12][13][14][15] were carried out in upper and lower limbs (large fiber nerves). The autonomic nervous system (small fibre nerves) was studied by means of heart rate variability at rest, sympathetic skin response and sudomotor test. Heart rate variability (HRV) at rest was evaluated recording the heart rate for 5 min [16]. Sympathetic skin response (SSR) was studied with electric stimuli over the Median and Posterior Tibial nerves, recording the responses over the palm of both hands (Median) and the sole of both feet (Tibial) [17,18]. Nerve conduction studies, HRV and SSR were performed by the same group of neurophysiologists with a 5-channel Natus ® Electromyography equipment. The sudomotor test, which gives the number of functioning sweat glands per cm 2 (sweat gland density, SGD) was obtained on a silicone mold after pilocarpine iontophoresis stimulation over the foot dorsum [19].
Genetic studies were realized by standard Sanger sequencing and Next Generation Sequencing (NGS) panels. Clinical severity score according to the first international consensus statement [1] was also studied (Table 1). Statistical studies were achieved with the SPSS program version 25.

Results
Conventional motor and sensory nerve conduction studies (large fiber nerves) were normal in all 20 individuals with CdLS analyzed (Additional file 1: Tables 1-3). The study of the autonomic nervous system (small fiber nerves) in HRV at rest was normal as well (Table 2). Nevertheless, SSR revealed mild alterations in lower limbs in 7 of the 20 individuals, with asymmetrical responses ( Table 2, Fig. 1). Sudomotor tests evinced reduced SGD in 16 of the 47 individuals with CdLS regarding the control group by decades of life (Table 3). The regression analysis showed that, in spite of dispersion, there were two different populations, with statistically significant differences between the control group and individuals with CdLS (p < 0.05 and p < 0.01) (Fig. 2). The linear regression showed that the slope of the SGD reduction by age is much more pronounced in individuals with CdLS than in controls (Fig. 2). Independence samples T test showed the results of the mean differences of the sweat gland density (SGD) by age group, with reduction in the SGD more evident in the individuals with variants in NIPBL than in the controls (p < 0.01). These differences were found in the whole NIPBL group as in all the decades of life, except the first one (Fig. 2, Table 4).
Genetic studies of the 47 individuals with CdLS revealed 31 with variants in NIPBL, 4 in SMC1A, 2 in RAD21, 2 in HDAC8 and 1 in SMC3 and negative in 7 individuals (Table 3). In Table 3 there are the CdLS Clinical Scores [1]. No relationship between clinical score or gastroesophageal reflux disease (GERD) and findings of the sudomotor test was found. In Additional file 1: Table 4 is shown the SGD in the control group by decades of life.

Discussion
Though the clinical manifestations of CdLS suggest that the peripheral nervous system is affected, large fiber nerve studies (conventional motor and sensory nerve conduction studies) are within normal limits. However, we have shown evidence, for the first time, for autonomic nervous system dysfunction in individuals with CdLS.
The sympathetic skin response reveals asymmetrical pathological responses in lower limbs in 7 of the 20 individuals (35%), with one of them affected in upper limbs as well. This could be considered a malformative manifestation of the syndrome. However, it is remarkable that the asymmetry is more frequent in lower than in upper limbs, which are often more affected [1][2][3][4]. This asymmetry does not seem to be related to GERD or the Clinical Severity Score (CSS), yet all the individuals had mutations in the NIPBL gene (Table 2).
Sudomotor testing shows a reduction in the sweat gland density (SGD) in 16 of 47 (34%) of the analyzed individuals with CdLS. These data are further supported by a reduction of the number of sweat droplets imprinted on the silicone after pilocarpine iontophoresis as indirect evidence of decreased postganglionic sudomotor nerve fibers, compared to an unaffected population. Though sweat gland density decreases physiologically with aging, individuals with CdLS show a reduction much greater than should be expected by their age. This decrease is evident from the second decade of life, and is more pronounced at older ages (Table 3, Fig. 2). All of this seems to strengthen the hypothesis that these patients have premature aging. Nevertheless, no relationships were found between SGD reduction and clinical score or GERD.
The reduction in the SGD is evident in individuals with mutations in NIPBL (Tables 3, 4), and seems to be similar in individuals with variants in SMC1A (3 of the 4 individuals with mutations in SMC1A had SGD reduction). However, individuals with variants in HDAC8 and RAD 21 are in the first decade of life, so it is early to make an assessment. Surprisingly, there is a high value of sweat  Clinical Score: ≥ 11 points, which at least 3 cardinal: classic CdLs; 9-10 points, which at least 2 cardinal: non-classic CdLs; 4-8 points, which at least 1 cardinal: molecular testing; < 4 points: insufficient to indicate molecular testing CdLs. Dotted individuals: involved genes different from NIPBL Table 2 Sympathetic skin response and heart rate variability in CdLS gland density in the only individual with an SMC3 mutation, who is 39 years old. Regarding the ethnic distribution, only 4 individuals in the NIPBL group and none in the control group were not Caucasian, and all of them had normal values in SGD, though they were in the first decade of life. In the group of NIPBL, there is a repeated    mutation, a frameshift mutation in 2 siblings. According to the asymmetry in the SSR response, 3 of the NIPBL individuals had missense mutations, 2 of them frameshift mutations and 1 of them splicing mutation, but the number of individuals is not big enough to do a correlation with the autonomic neuropathy. Further studies are warranted to look at autonomic nervous system dysfunction and relation to mutated gene and age in individuals with CdLS.

Conclusion
Individuals with CdLS have abnormal autonomic nervous system function, showing asymmetries in the sympathetic responses in lower limbs, and pathological results in the sudomotor test. The degree of dysfunction in postganglionic sudomotor nerve fibers might be related to premature aging. Even though, somatic nervous system function studies were normal.