Isolated neurological presentations of mevalonate kinase deficiency

Mevalonate kinase (MK) deficiency is a rare autosomal recessive metabolic disorder caused by pathogenic variants in the MVK gene with a broad phenotypic spectrum including autoinflammation, developmental delay and ataxia. Typically, neurological symptoms are considered to be part of the severe end of the phenotypical spectrum and are reported to be in addition to the autoinflammatory symptoms. Here, we describe a patient with MK deficiency with severe neurological symptoms but without autoinflammation and we found several similar patients in the literature. Possibly, the non‐inflammatory phenotype is related to a specific genotype: the MVK p.(His20Pro)/p.(Ala334Thr) variant. There is probably an underdetection of the neurological MK deficient phenotype without inflammatory symptoms as clinicians may not test for MK deficiency when patients present with only neurological symptoms. In conclusion, although rare, neurological symptoms without hyperinflammation might be more common than expected in MK deficiency. It seems relevant to consider MK deficiency in patients with psychomotor delay and ataxia, even if there are no inflammatory symptoms

Preface

AimThis was a one-year follow-up of families referred to support services after the parents visited the emergency department due to intimate partner violence, substance abuse or a suicide attempt. Its aim was to evaluate the well-being of any children. MethodsData on families identified a year earlier by the Amsterdam protocol were gathered from child protective services and parent and child self-reports in two Dutch regions from 2012-2015. ResultsWe included 399 children (52%) boys with a median age of eight years (range 1-18) in the study using child protective services data. Of the 101 families who participated in the first measurement, 67 responded one year after the parent's emergency department visit. The results showed that 20% of the children had no or minor problems, voluntary support services were involved in 60% of cases and child protective services were involved in 20%. Compared to their first assessment a year earlier, the children's psychosocial problems had not increased, but this could have been an underestimation due to selective responses. ConclusionThe Amsterdam protocol was valuable in referring families to voluntary support services, but given the ongoing problems in some families, professionals need to carefully monitor whether support services are sufficiently effectiv

Mono-allelic KCNB2 variants lead to a neurodevelopmental syndrome caused by altered channel inactivation

International audienceIon channels mediate voltage fluxes or action potentials that are central to the functioning of excitable cells such as neurons. The KCNB family of voltage-gated potassium channels (Kv) consists of two members (KCNB1 and KCNB2) encoded by KCNB1 and KCNB2, respectively. These channels are major contributors to delayed rectifier potassium currents arising from the neuronal soma which modulate overall excitability of neurons. In this study, we identified several mono-allelic pathogenic missense variants in KCNB2, in individuals with a neurodevelopmental syndrome with epilepsy and autism in some individuals. Recurrent dysmorphisms included a broad forehead, synophrys, and digital anomalies. Additionally, we selected three variants where genetic transmission has not been assessed, from two epilepsy studies, for inclusion in our experiments. We characterized channel properties of these variants by expressing them in oocytes of Xenopus laevis and conducting cut-open oocyte voltage clamp electrophysiology. Our datasets indicate no significant change in absolute conductance and conductance-voltage relationships of most disease variants as compared to wild type (WT), when expressed either alone or co-expressed with WT-KCNB2. However, variants c.1141A>G (p.Thr381Ala) and c.641C>T (p.Thr214Met) show complete abrogation of currents when expressed alone with the former exhibiting a left shift in activation midpoint when expressed alone or with WT-KCNB2. The variants we studied, nevertheless, show collective features of increased inactivation shifted to hyperpolarized potentials. We suggest that the effects of the variants on channel inactivation result in hyper-excitability of neurons, which contributes to disease manifestations

Mono-allelic KCNB2 variants lead to a neurodevelopmental syndrome caused by altered channel inactivation

Ion channels mediate voltage fluxes or action potentials that are central to the functioning of excitable cells such as neurons. The KCNB family of voltage-gated potassium channels (Kv) consists of two members (KCNB1 and KCNB2) encoded by KCNB1 and KCNB2, respectively. These channels are major contributors to delayed rectifier potassium currents arising from the neuronal soma which modulate overall excitability of neurons. In this study, we identified several mono-allelic pathogenic missense variants in KCNB2, in individuals with a neurodevelopmental syndrome with epilepsy and autism in some individuals. Recurrent dysmorphisms included a broad forehead, synophrys, and digital anomalies. Additionally, we selected three variants where genetic transmission has not been assessed, from two epilepsy studies, for inclusion in our experiments. We characterized channel properties of these variants by expressing them in oocytes of Xenopus laevis and conducting cut-open oocyte voltage clamp electrophysiology. Our datasets indicate no significant change in absolute conductance and conductance-voltage relationships of most disease variants as compared to wild type (WT), when expressed either alone or co-expressed with WT-KCNB2. However, variants c.1141A>G (p.Thr381Ala) and c.641C>T (p.Thr214Met) show complete abrogation of currents when expressed alone with the former exhibiting a left shift in activation midpoint when expressed alone or with WT-KCNB2. The variants we studied, nevertheless, show collective features of increased inactivation shifted to hyperpolarized potentials. We suggest that the effects of the variants on channel inactivation result in hyper-excitability of neurons, which contributes to disease manifestations