SLC6A1 variant pathogenicity, molecular function and phenotype: a genetic and clinical analysis

Genetic variants in the SLC6A1 gene can cause a broad phenotypic disease spectrum by altering the protein function. Thus, systematically curated clinically relevant genotype-phenotype associations are needed to understand the disease mechanism and improve therapeutic decision-making. We aggregated genetic and clinical data from 172 individuals with likely pathogenic/pathogenic (lp/p) SLC6A1 variants and functional data for 184 variants (14.1% lp/p). Clinical and functional data were available for a subset of 126 individuals. We explored the potential associations of variant positions on the GAT1 3D structure with variant pathogenicity, altered molecular function and phenotype severity using bioinformatic approaches. The GAT1 transmembrane domains 1, 6 and extracellular loop 4 (EL4) were enriched for patient over population variants. Across functionally tested missense variants (n = 156), the spatial proximity from the ligand was associated with loss-of-function in the GAT1 transporter activity. For variants with complete loss of in vitro GABA uptake, we found a 4.6-fold enrichment in patients having severe disease versus non-severe disease (P = 2.9 × 10-3, 95% confidence interval: 1.5-15.3). In summary, we delineated associations between the 3D structure and variant pathogenicity, variant function and phenotype in SLC6A1-related disorders. This knowledge supports biology-informed variant interpretation and research on GAT1 function. All our data can be interactively explored in the SLC6A1 portal (https://slc6a1-portal.broadinstitute.org/).

Long time polysomnographic sleep and breathing evaluations in children with CDKL5 deficiency disorder

STUDY OBJECTIVES

CDKL5 deficiency disorder (CDD) is a rare developmental and epileptic encephalopathy, developing in the first months of life, caused by a mutation in the cyclin-dependent kinase-like 5 (CDKL5) gene. Children with CDD often have sleep (90%) and breathing disorders in wake (50%). Sleep disorders may have a significant impact emotional wellbeing and quality of life of caregivers of children with CDD and are challenging to treat. The outcomes of these features are unknown in children with CDD.

METHODS

We retrospectively evaluated sleep and respiratory function changes over 5-10 years in a small cohort of Dutch children with CDD, using video-EEG and/or polysomnography (3 × 24 h) and a parental questionnaire, the Sleep Disturbance Scale for Children (SDSC). The present study is a follow-up sleep and PSG study to evaluate if sleep and breathing disturbances persist in children with CDD previously studied.

RESULTS

Sleep disturbances persisted during the study period (5.5-10 years). All five individuals had long sleep latency (SL, range 32-174.5 min) and frequent arousals and awakenings (14-50/night), unrelated to apneas/seizures, corresponding to the SDSC findings. Low sleep efficiency (SE, 41-80%) was present and did not improve. In our participants, total sleep time (TST, 3h52min-7h52min) was short and remained so. Time in bed (TIB) was typical for children aged 2-8 years, but did not adjust with ageing. Low duration (4.8-17.4%) or even absent REM sleep persisted over time. No sleep apneas were noted. Central apneas due to episodic hyperventilation were reported during wakefulness in two of the five.

CONCLUSION

Sleep disturbances were present and persisted in all. The decreased REM sleep and sporadic breathing disturbances in wake may indicate failure of brainstem nuclei. Sleep disturbances can severely affect the emotional wellbeing and quality of life of the caregivers and the individuals with CDD and are challenging to treat. Hopefully our polysomnographic sleep data contribute to find the optimal treatment of the sleep problems in CDD patients.

Parental experiences and perspectives on the value of seizure detection while caring for a child with epilepsy: A qualitative study

INTRODUCTION

Caring for a child with epilepsy has a significant impact on parental quality of life. Seizure unpredictability and complications, including sudden unexpected death in epilepsy (SUDEP), may cause high parental stress and increased anxiety. Nocturnal supervision with seizure detection devices may lower SUDEP risk and decrease parental burden of seizure monitoring, but little is known about their added value in family homes.

METHODS

We conducted semi-structured in-depth interviews with parents of children with refractory epilepsy participating in the PROMISE trial (NCT03909984) to explore the value of seizure detection in the daily care of their child. Children were aged 4-16 years, treated at a tertiary epilepsy center, had at least one nocturnal major motor seizure per week, and used a wearable seizure detection device (NightWatch) for two months at home. Data were analyzed using inductive thematic analysis.

RESULTS

Twenty three parents of nineteen children with refractory epilepsy were interviewed. All parents expressed their fear of missing a large seizure and the possible consequences of not intervening in time. Some parents felt the threat of child loss during every seizure, while others thought about it from time to time. The fear could fluctuate over time, mainly associated with fluctuations of seizure frequency. Most parents described how they developed a protective behavior, driven by this fear. The way parents handled the care of their child and experienced the burden of care influenced their perceptions on the added value of NightWatch. The experienced value of NightWatch depended on the amount of assurance it could offer to reduce their fear and the associated protective behavior as well as their resilience to handle the potential extra burden of care, due to false alarms or technical problems.

CONCLUSION

Healthcare professionals and device companies should be aware of parental protective behavior and the high parental burden of care and develop tailored strategies to optimize seizure detection device care.

Two Siblings With a CDKL5 Mutation: Genotype and Phenotype Evaluation

This is the second report of a family with a recurrence of a CDKL5 mutation (c. 283-3_290del) in 2 sisters. Both parents tested negative for the mutation in all tissues, but germline mosaicism is likely. Clinically CDKL5 patients resemble those with Rett syndrome, caused by a MECP2 mutation, who experience a regression, after an initial normal development. Even though both siblings showed a typical CDKL5 phenotype, their presentation is different. From birth, the oldest daughter had a severe developmental delay, feeding problems, and hypotonia and experienced daily refractory seizures. The youngest daughter appeared to be normal until age 3 months. At that age seizures started, deterioration and regression became evident, and an epileptic encephalopathy developed. This report of familial recurrence, with suspected germline mosaicism in a healthy parent, has important consequences for genetic counseling. Although it is not possible to predict an exact recurrence risk, it is likely to be increased.

S-adenosylmethionine and S-adenosylhomocysteine in plasma and cerebrospinal fluid in Rett syndrome and the effect of folinic acid supplementation

Rett syndrome is a neurodevelopmental disorder characterized by cognitive and locomotor regression and stereotypic hand movements. The disorder is caused by mutations in the X chromosomal MECP2 a gene encoding methyl CpG-binding protein. It has been associated with disturbances of cerebral folate homeostasis, as well as with speculations on a compromised DNA-methylation. Folinic acid is the stable form of folate. Its derived intermediate 5-MTHF supports the conversion of homocysteine to methionine, the precursor of S-adenosylmethionine (SAM). This in turn donates its methyl group to various acceptors, including DNA, thereby being converted to S-adenosylhomocysteine (SAH). The SAM/SAH ratio reflects the methylation potential. The goal of our study was to influence DNA methylation processes and ameliorate the clinical symptoms in Rett syndrome. Therefore we examined the hypothesis that folinic acid supplementation, besides increasing cerebrospinal fluid (CSF) 5-MTHF (p = 0.003), influences SAM and SAH and their ratio. In our randomized, double-blind crossover study on folinic acid supplementation, ten female Rett patients received both folinic acid and placebo for 1 year each. It was shown that both SAM and SAH levels in the CSF remained unchanged following folinic acid administration (p = 0.202 and p = 0.097, respectively) in spite of a rise of plasma SAM and SAH (p = 0.007; p = 0.009). There was no significant change in the SAM/SAH ratio either in plasma or CSF. The apparent inability of Rett patients to upregulate SAM and SAH levels in the CSF may contribute to the biochemical anomalies of the Rett syndrome. Our studies warrant further attempts to promote DNA methylation in the true region of interest, i.e. the brain.

Respiratory and sleep disorders in female children with atypical Rett syndrome caused by mutations in the CDKL5 gene

AIM

In female children with drug-resistant seizures and developmental delay from birth, atypical Rett syndrome caused by mutations in the CDKL5 gene should be considered. Several clinical features resemble classic Rett syndrome. Respiratory and sleep abnormalities are frequently present in Rett syndrome, whereas little is known in patients with CDKL5 mutations.

METHOD

In four genetically confirmed female patients with CDKL5 mutations (age range 2-15 y), the presence of breathing and sleep abnormalities was evaluated using the validated Sleep Disturbance Scale for Children and polysomnography (PSG).

RESULTS

The Sleep Disturbance Scale for Children indicated disorders of initiating and maintaining sleep, daytime somnolence, and sleep breathing disorders. In one patient, PSG showed central apnoeas during sleep: her total apnoea-hypopnoea index (AHI) was 4.9, of which the central AHI was 3.4/h. When awake, central apnoeas were present in two of the four female children (central AHI 28/h and 41/h respectively), all preceded by hyperventilation. PSG showed low rapid eye movement (REM) sleep (9.7-18.3%), frequent awakenings, and low sleep efficiency (range 59-78%).

INTERPRETATION

Episodic hyperventilation followed by central apnoeas was present while awake in two of four patients. This may indicate failure of brainstem respiratory centres. In addition, low REM sleep, frequent arousals (not caused by apnoeas/seizures), and low sleep efficiency were present. Similar to Rett syndrome, in patients with CDKL5 mutations PSG seems warranted to evaluate breathing and sleep disturbances.

Respiratory disturbances in rett syndrome: don't forget to evaluate upper airway obstruction

Rett syndrome is characterized by loss of motor and social functions, development of stereotypic hand movements, seizures, and breathing disturbances. This study evaluates the presence of overnight respiratory disturbances. Polysomnography in combination with a questionnaire (the Sleep Disturbance Scale for Children) was performed in 12 Dutch patients with Rett. Respiratory disturbances were present in all, clinically relevant in 10 (apnea hypopnea per hour 1.0-14.5). In 8 children, central apneas were present during the day often with obstructive apneas at night. In 6, obstructive sleep apnea syndrome was diagnosed, in 3 severe, with frequent oxygen desaturations. Significant respiratory complaints were present in 3 patients, all had obstructive sleep apnea syndrome. Of the 12 patients with Rett, 8 (67%) snored, and in 5 obstructive sleep apnea syndrome was present. In children, hypertrophied tonsils and adenoids are a common cause of obstructive sleep apnea syndrome, which may benefit from therapeutic intervention. We recommend performing polysomnography in patients with Rett syndrome and respiratory complaints.

Folinic acid supplementation in Rett syndrome patients does not influence the course of the disease: a randomized study

Rett syndrome is a neurodevelopmental disorder in girls, related to mutations in MECP2 gene. It has been postulated that low 5-methyltetrahydrofolate (5-MTHF) levels are present in cerebrospinal fluid. Folinic acid demonstrated clinical improvement. However, because studies have produced conflicting results, we performed a randomized, double-blind crossover, long-term, follow-up study on folinic acid. Eight Rett syndrome patients received both folinic acid and placebo, for 1 year each. Measurements included plasma folate, 5-MTHF, and clinical outcome scores like Rett Syndrome Motor Behavioral Assessment, Hand Apraxia Scale, and the parental Overall Well-Being Index. In 2 patients, low 5-MTHF levels were present. Folinic acid supplementation increased cerebrospinal fluid 5-MTHF levels, but with no objective evidence of clinical improvement. The Overall Well-Being Index showed a significant difference in favor of folinic acid, not confirmed objectively. In our double-blind randomized study, folinic acid supplementation resulted in increased 5-MTHF levels, but with no objective signs of clinical improvement.

Clinical and electroencephalographic effects of folinic acid treatment in Rett syndrome patients

Rett syndrome is characterized by the development of stereotypic hand movements and seizures, which are often difficult to treat. Previous studies have shown conflicting results during add-on folinic acid. Here, the authors reevaluate the response to folinic acid in terms of epilepsy control and electroencephalography features. They performed a randomized, placebo-controlled, double-blind crossover trial, with a follow-up of more than 2 years. Twelve girls with Rett syndrome participated, comparable in clinical stage and disease severity. The Rett syndrome patients were given either folinic acid or placebo, for 1 year each. Only 3 girls benefited to some extent: 2 had a reduction and/or decrease in seizures, and all 3 showed some decreased epileptiform activity on electroencephalography during the addition of folinic acid. Despite this, antiepileptic drugs were adjusted. Because the effect of added folinic acid was limited and did not prevent antiepileptic drug increase, the authors do not recommend adding on folinic acid in Rett syndrome girls with epilepsy.

[Staring episodes in children with developmental disorders: epilepsy or behaviour?]

Behavioural episodes of staring in children are difficult to distinguish from epileptic seizures, especially in children with developmental disorders such as ADHD, autism spectrum disorders and intellectual disabilities. We discuss two patients with staring episodes who were using anti-epileptic drugs. In both patients, EEG with video monitoring showed that the staring was non-epileptic. The first is an 8-year-old boy, who developed severe motor problems and ataxia during treatment with valproate. His staring episodes were behavioural, caused by his intellectual disability, and the motor problems resolved after discontinuation of valproate. The second patient is a 10-year-old boy with known autism, ADHD and infantile seizures, who developed staring for which he was using valproate. Again, video-EEG monitoring during staring showed no abnormalities and in this case the staring was caused by his intellectual disability and autism. We discuss the differential diagnosis of staring episodes in children with developmental disorders and present the pitfalls of the diagnostic process.

Magnetic resonance imaging of the lumbosacral spine in children with chronic constipation or non-retentive fecal incontinence: a prospective study

OBJECTIVE

To determine the prevalence of lumbosacral spine (LSS) abnormalities in children with defecation disorders, intractable constipation, or non-retentive fecal incontinence (NRFI) and evaluate whether LSS abnormalities on magnetic resonance imaging (MRI) are clinically detected by neurologic examination.

STUDY DESIGN

MRI of the LSS and complete neurologic examination by a pediatric neurologist blinded to the MRI results were performed in patients with intractable defecation disorders.

RESULTS

Patients with intractable constipation (n = 130; 76 males; median age, 11 years; range, 6-18 years), and patients with NRFI (n = 28; 18 males; median age, 10 years; range, 7-15 years) participated. One occult spina bifida (OSB) and 3 terminal filum lipomas were found in patients with a normal neurologic examination. One patient had a terminal filum lipoma and neurologic complaints. Gluteal cleft deviation was found in 3 of 4 patients with LSS abnormalities. Neurosurgical treatment was not required in any patient during the 12-week follow-up.

CONCLUSIONS

MRI showed LSS abnormalities in 3% of patients with defecation disorders and normal neurologic examination, all of whom reported symptom relief at the 12-week follow-up without neurosurgical intervention. Thus, whether or not LSS abnormalities play a role in defecation disorders remains unclear.

A case of neonatal dural sinus malformation: clinical symptoms, imaging and neuropathological investigations

We report a case of neonatal dural sinus malformation already visible on antenatal ultrasound. This is a rare disease entity in infants and children. Clinical diagnosis was made by demonstrating a cranial murmur on auscultation; macrocrania and signs of progressive cardiac failure. Imaging studies as cerebral ultrasound, postnatal MRI scan and MR angiography demonstrated a large dural sinus malformation originating from the sagittal sinus with extensive arteriovenous fistulae. Due to the extent of the lesion, the existing ischemic brain damage and involvement of the torcular, no therapeutic options were available and the child died of irreversible cardiac failure. The diagnosis was confirmed with autopsy. We discuss the clinical presentation, imaging and neuropathological results and relate our findings to embryological data and the existing literature.

Molecular and clinical characterization of a Moroccan Cog7 deficient patient

Mutations in the N-linked glycosylation pathway cause rare autosomal recessive defects known as Congenital Disorders of Glycosylation (CDG). A previously reported mutation in the Conserved Oligomeric Golgi complex gene, COG7, defined a new subtype of CDG in a Tunisian family. The mutation disrupted the hetero-octomeric COG complex and altered both N- and O-linked glycosylation. Here we present clinical and biochemical data from a second family with the same mutation.

Bobble-head doll syndrome successfully treated with an endoscopic ventriculocystocisternostomy. Case report and review of the literature

The bobble-head doll syndrome (BHDS) is characterized by a back-and-forth movement of the head with a frequency of 2 to 3 Hz, which increases during walking and excitement and decreases during concentration. The head movements are accompanied by macrocephaly, ocular disturbances, psychomotor retardation, and sometimes endocrine dysfunction. The BHDS is frequently associated with a suprasellar arachnoid cyst. The authors present the case of a 4-year-old patient with BHDS; an endoscopic cystoventriculostomy was performed by fenestrating a cyst in the suprasellar region. After wide fenestration of the cyst wall that was protruding and obstructing the foramen of Monro, the cyst was entered with the endoscope and a small, natural, valvelike communication of the cyst with the basal prepontine cistern was seen close to the basilar artery. This communication was widened by balloon dilation. After completion of the ventriculocystocisternostomy, the cyst collapsed and the obstruction of the aqueduct was resolved. In view of the source mechanism and cerebrospinal fluid dynamics of the suprasellar arachnoid cyst, a ventriculocystocisternostomy is an important treatment option for BHDS arising from a suprasellar cyst. Three years after treatment, the head bobbing had resolved completely and psychomotor development was improving. Delay of diagnosis and treatment of this condition can cause permanent neurological dysfunction and psychomotor retardation. The authors recommend early ventriculocystocisternostomy as a physiologically based treatment for BHDS originating from a suprasellar cyst.

Clinical and electrophysiological follow-up after local steroid injection in the carpal tunnel syndrome

OBJECTIVE

Local steroid injections are used for treatment for the carpal tunnel syndrome (CTS). Study of changes in neurophysiological parameters after such treatment for idiopathic CTS might be a supportive argument for the effectiveness of steroid treatment.

METHODS

Twenty-one patients with CTS were included and evaluated before and at 1, 3 and 6 months after treatment. At the inclusion date patients received a single 1 ml local steroid injection. Various electrophysiological tests were used. For clinical evaluation, we used the Boston Carpal Tunnel Questionnaire (BCTQ) and the General Outcome Score.

RESULTS

The mean nerve conduction parameters had significantly improved at 1 month, except the SNAP4 and CMAP. This improvement was still present at 3 months. At 6 months follow-up, the improvement in the SDL4, SNAP4, M-U, DML and CMAP remained significant. In 6 patients (29%), the nerve conduction parameters normalized and remained so until the end of the study. The BCTQ and the General Outcome Score significantly improved as well. However, there was no correlation between the electrophysiological data, the BCTQ and the General Outcome Score.

CONCLUSIONS

The improvements of nerve conduction parameters independently support the ideas on effectiveness of steroid injection therapy in CTS.