MAGEL2 (patho-)physiology and Schaaf-Yang syndrome

Schaaf-Yang syndrome (SYS) is a complex neurodevelopmental disorder characterized by autism spectrum disorder, joint contractures, and profound hypothalamic dysfunction. SYS is caused by variants in MAGEL2, a gene within the Prader-Willi syndrome (PWS) locus on chromosome 15. In this review, we consolidate decades of research on MAGEL2 to elucidate its physiological functions. Moreover, we synthesize current knowledge on SYS, suggesting that while MAGEL2 loss-of-function seems to underlie several SYS and PWS phenotypes, additional pathomechanisms probably contribute to the distinct and severe phenotype observed in SYS. In addition, we highlight recent therapeutic advances and identify promising avenues for future investigation.

CLCF1 inhibits energy expenditure via suppressing brown fat thermogenesis

Brown adipose tissue (BAT) is the main site of nonshivering thermogenesis which plays an important role in thermogenesis and energy metabolism. However, the regulatory factors that inhibit BAT activity remain largely unknown. Here, cardiotrophin-like cytokine factor 1 (CLCF1) is identified as a negative regulator of thermogenesis in BAT. Adenovirus-mediated overexpression of CLCF1 in BAT greatly impairs the thermogenic capacity of BAT and reduces the metabolic rate. Consistently, BAT-specific ablation of CLCF1 enhances the BAT function and energy expenditure under both thermoneutral and cold conditions. Mechanistically, adenylate cyclase 3 (ADCY3) is identified as a downstream target of CLCF1 to mediate its role in regulating thermogenesis. Furthermore, CLCF1 is identified to negatively regulate the PERK-ATF4 signaling axis to modulate the transcriptional activity of ADCY3, which activates the PKA substrate phosphorylation. Moreover, CLCF1 deletion in BAT protects the mice against diet-induced obesity by promoting BAT activation and further attenuating impaired glucose and lipid metabolism. Therefore, our results reveal the essential role of CLCF1 in regulating BAT thermogenesis and suggest that inhibiting CLCF1 signaling might be a potential therapeutic strategy for improving obesity-related metabolic disorders.

New insights into the physiology and pathophysiology of the atypical sodium leak channel NALCN

Cell excitability and its modulation by hormones and neurotransmitters involve the concerted action of a large repertoire of membrane proteins, especially ion channels. Unique complements of coexpressed ion channels are exquisitely balanced against each other in different excitable cell types, establishing distinct electrical properties that are tailored for diverse physiological contributions, and dysfunction of any component may induce a disease state. A crucial parameter controlling cell excitability is the resting membrane potential (RMP) set by extra- and intracellular concentrations of ions, mainly Na+, K+, and Cl-, and their passive permeation across the cell membrane through leak ion channels. Indeed, dysregulation of RMP causes significant effects on cellular excitability. This review describes the molecular and physiological properties of the Na+ leak channel NALCN, which associates with its accessory subunits UNC-79, UNC-80, and NLF-1/FAM155 to conduct depolarizing background Na+ currents in various excitable cell types, especially neurons. Studies of animal models clearly demonstrate that NALCN contributes to fundamental physiological processes in the nervous system including the control of respiratory rhythm, circadian rhythm, sleep, and locomotor behavior. Furthermore, dysfunction of NALCN and its subunits is associated with severe pathological states in humans. The critical involvement of NALCN in physiology is now well established, but its study has been hampered by the lack of specific drugs that can block or agonize NALCN currents in vitro and in vivo. Molecular tools and animal models are now available to accelerate our understanding of how NALCN contributes to key physiological functions and the development of novel therapies for NALCN channelopathies.

Clinical and molecular genetic findings of Crisponi / cold-induced sweating syndrome (CS/CISS) spectrum in patients from Turkey

Crisponi / cold-induced sweating syndrome (CS/CISS) is a rare autosomal recessive disorder characterized by episodic hyperthermia, arthrogryposis, impaired feeding ability, and respiratory distress. The classic CS/CISS is mainly associated with CRLF1 and, rarely, CLCF1. PERCHING syndrome, previously known as CS/CISS type-3 associated with biallelic pathogenic variants in KLHL7, is notable for its few overlapping manifestations. This study presents genotype-phenotype relationships in CS/CISS-like spectrum associated with CRLF1 and KLHL7. Clinical findings of 19 patients from 14 families and four patients from three families were found in association with six different CRLF1 and three different KLHL7 variants, respectively. c.167 T > C and c.713delC of the CRLF1 gene and the c.642G > C of the KLHL7 were novel. The c.708_709delCCinsT allele of CRLF1 was identified in 10 families from the Mardin province of Turkey, underlining that an ancestral haplotype has become widespread. CRLF1-associated phenotypes revealed novel manifestations such as prenatal oligohydramnios, benign external hydrocephalus, previously unreported dysmorphic features emerging with advancing age, severe palmoplantar keratoderma and facial erythema, hypopigmented macules and streaks, and recurrent cardiac arrests. KLHL7 variants presented with glabellar nevus flammeus, blepharophimosis, microcephaly, thin corpus callosum, and cleft palate. Abnormalities of sweating, observed in one patient reported herein, is known to be very rare among KLHL7-related phenotypes. This article is protected by copyright. All rights reserved.

Three new cases of Crisponi /cold induced sweating syndrome (CS/CISS1) in Turkish families

Crisponi syndrome/Cold Induced Sweating Syndrome 1 (CS/CISS1) is a rare, autosomal recessive, multisystemic disease. Hyperthermia attacks, abnormal contractions in the muscles of the face and oropharynx, respiratory distress, camptodactyly, and swallowing difficulty are the main features of the condition in the neonatal period. Patients experience cold-induced sweating attacks and progressive kyphoscoliosis in childhood and adolescence. Mutations in the cytokine receptor like factor 1 (CRLF1) gene causes the CISS1 (Cold- induced sweating syndrome type 1) disease (over 95% of patients). CRLF1 is located in the ciliary neurotrophic factor receptor (CNTFR) pathway, which plays an important role in development and maintenance of neurons in the nervous system. In this study three patients from Turkey, clinically and molecularly diagnosed with CS/CISS1, are presented. Hyperthermia, swallowing difficulty, camptodactyly and pursing of the lips were present in all patients, and foot deformity in one patient. In the first patient a homozygous nonsense mutation NM_004750.5: c.531G > A; p.(Trp177Ter) in the 4th exon was detected. In the second patient a homozygous nonsense mutation NM_004750.5: c.776C > A; p.(Ser259Ter) in the 5th exon was detected. The third patient was homozygous for a missense mutation NM_004750.5: c.935G > T; p.(Arg312Leu) in the 6th exon. Early diagnosis is very important in this syndrome since most patients die in the neonatal period. Therefore, physicians should be suspicious for this disease in patients with dysmorphic features, hyperthermia attacks, camptodactyly, pursing of lips while crying, and swallowing difficulty.

Functional expression of CLIFAHDD and IHPRF pathogenic variants of the NALCN channel in neuronal cells reveals both gain- and loss-of-function properties

The excitability of neurons is tightly dependent on their ion channel repertoire. Among these channels, the leak sodium channel NALCN plays a crucial role in the maintenance of the resting membrane potential. Importantly, NALCN mutations lead to complex neurodevelopmental syndromes, including infantile hypotonia with psychomotor retardation and characteristic facies (IHPRF) and congenital contractures of limbs and face, hypotonia and developmental delay (CLIFAHDD), which are recessively and dominantly inherited, respectively. Unfortunately, the biophysical properties of NALCN are still largely unknown to date, as well as the functional consequences of both IHPRF and CLIFAHDD mutations on NALCN current. Here we have set-up the heterologous expression of NALCN in the neuronal cell line NG108-15 to investigate the electrophysiological properties of NALCN carrying representative IHPRF and CLIFAHDD mutations. Several original properties of the wild-type (wt) NALCN current were retrieved: mainly carried by external Na⁺, blocked by Gd³⁺, insensitive to TTX and potentiated by low external Ca²⁺ concentration. However, we found that this current displays a time-dependent inactivation in the −80/−40 mV range of membrane potential, and a non linear current-voltage relationship indicative of voltage sensitivity. Importantly, no detectable current was recorded with the IHPRF missense mutation p.Trp1287Leu (W1287L), while the CLIFAHDD mutants, p.Leu509Ser (L509S) and p.Tyr578Ser (Y578S), showed higher current densities and slower inactivation, compared to wt NALCN current. This study reveals that heterologous expression of NALCN channel can be achieved in the neuronal cell line NG108-15 to study the electrophysiological properties of wt and mutants. From our results, we conclude that IHPRF and CLIFAHDD missense mutations are loss- and gain-of-function variants, respectively.