Bi-allelic Mutations in LSS, Encoding Lanosterol Synthase, Cause Autosomal-Recessive Hypotrichosis Simplex.

Hypotrichosis simplex (HS) is a rare form of hereditary alopecia characterized by childhood onset of diffuse and progressive scalp and body hair loss. Although research has identified a number of causal genes, genetic etiology in about 50% of HS cases remains unknown. The present report describes the identification via whole-exome sequencing of five different mutations in the gene LSS in three unrelated families with unexplained, potentially autosomal-recessive HS. Affected individuals showed sparse to absent lanugo-like scalp hair, sparse and brittle eyebrows, and sparse eyelashes and body hair. LSS encodes lanosterol synthase (LSS), which is a key enzyme in the cholesterol biosynthetic pathway. This pathway plays an important role in hair follicle biology. After localizing LSS protein expression in the hair shaft and bulb of the hair follicle, the impact of the mutations on keratinocytes was analyzed using immunoblotting and immunofluorescence. Interestingly, wild-type LSS was localized in the endoplasmic reticulum (ER), whereas mutant LSS proteins were localized in part outside of the ER. A plausible hypothesis is that this mislocalization has potential deleterious implications for hair follicle cells. Immunoblotting revealed no differences in the overall level of wild-type and mutant protein. Analyses of blood cholesterol levels revealed no decrease in cholesterol or cholesterol intermediates, thus supporting the previously proposed hypothesis of an alternative cholesterol pathway. The identification of LSS as causal gene for autosomal-recessive HS highlights the importance of the cholesterol pathway in hair follicle biology and may facilitate novel therapeutic approaches for hair loss disorders in general.

Confirmation of Ogden syndrome as an X-linked recessive fatal disorder due to a recurrent NAA10 variant and review of the literature.

Ogden syndrome is a rare lethal X-linked recessive disorder caused by a recurrent missense variant (Ser37Pro) in the NAA10 gene, encoding the catalytic subunit of the N-terminal acetyltransferase A complex (NatA). So far eight boys of two different families have been described in the literature, all presenting the distinctive and recognizable phenotype, which includes mostly postnatal growth retardation, global severe developmental delay, characteristic craniofacial features, and structural cardiac anomalies and/or arrhythmias. Here, we report the ninth case of Ogden syndrome with an independent recurrence of the Ser37Pro variant. We were able to follow the clinical course of the affected boy and delineate the evolving phenotype from his birth until his unfortunate death at 7 months. We could confirm the associated phenotype as well as the natural history of this severe disease. By describing new presenting features, we are further expanding the clinical spectrum associated with Ogden syndrome and review other phenotypes associated with NAA10 variants.

Overlapping SETBP1 gain-of-function mutations in Schinzel-Giedion syndrome and hematologic malignancies.

Schinzel-Giedion syndrome (SGS) is a rare developmental disorder characterized by multiple malformations, severe neurological alterations and increased risk of malignancy. SGS is caused by de novo germline mutations clustering to a 12bp hotspot in exon 4 of SETBP1. Mutations in this hotspot disrupt a degron, a signal for the regulation of protein degradation, and lead to the accumulation of SETBP1 protein. Overlapping SETBP1 hotspot mutations have been observed recurrently as somatic events in leukemia. We collected clinical information of 47 SGS patients (including 26 novel cases) with germline SETBP1 mutations and of four individuals with a milder phenotype caused by de novo germline mutations adjacent to the SETBP1 hotspot. Different mutations within and around the SETBP1 hotspot have varying effects on SETBP1 stability and protein levels in vitro and in in silico modeling. Substitutions in SETBP1 residue I871 result in a weak increase in protein levels and mutations affecting this residue are significantly more frequent in SGS than in leukemia. On the other hand, substitutions in residue D868 lead to the largest increase in protein levels. Individuals with germline mutations affecting D868 have enhanced cell proliferation in vitro and higher incidence of cancer compared to patients with other germline SETBP1 mutations. Our findings substantiate that, despite their overlap, somatic SETBP1 mutations driving malignancy are more disruptive to the degron than germline SETBP1 mutations causing SGS. Additionally, this suggests that the functional threshold for the development of cancer driven by the disruption of the SETBP1 degron is higher than for the alteration in prenatal development in SGS. Drawing on previous studies of somatic SETBP1 mutations in leukemia, our results reveal a genotype-phenotype correlation in germline SETBP1 mutations spanning a molecular, cellular and clinical phenotype.

Further corroboration of distinct functional features in SCN2A variants causing intellectual disability or epileptic phenotypes.

BACKGROUND: Deleterious variants in the voltage-gated sodium channel type 2 (Nav1.2) lead to a broad spectrum of phenotypes ranging from benign familial neonatal-infantile epilepsy (BFNIE), severe developmental and epileptic encephalopathy (DEE) and intellectual disability (ID) to autism spectrum disorders (ASD). Yet, the underlying mechanisms are still incompletely understood. METHODS: To further elucidate the genotype-phenotype correlation of SCN2A variants we investigated the functional effects of six variants representing the phenotypic spectrum by whole-cell patch-clamp studies in transfected HEK293T cells and in-silico structural modeling. RESULTS: The two variants p.L1342P and p.E1803G detected in patients with early onset epileptic encephalopathy (EE) showed profound and complex changes in channel gating, whereas the BFNIE variant p.L1563V exhibited only a small gain of channel function. The three variants identified in ID patients without seizures, p.R937C, p.L611Vfs*35 and p.W1716*, did not produce measurable currents. Homology modeling of the missense variants predicted structural impairments consistent with the electrophysiological findings. CONCLUSIONS: Our findings support the hypothesis that complete loss-of-function variants lead to ID without seizures, small gain-of-function variants cause BFNIE and EE variants exhibit variable but profound Nav1.2 gating changes. Moreover, structural modeling was able to predict the severity of the variant impact, supporting a potential role of structural modeling as a prognostic tool. Our study on the functional consequences of SCN2A variants causing the distinct phenotypes of EE, BFNIE and ID contributes to the elucidation of mechanisms underlying the broad phenotypic variability reported for SCN2A variants.

A recurrent germline mutation in the PIGA gene causes Simpson-Golabi-Behmel syndrome type 2.

Hypomorphic germline mutations in the PIGA (phosphatidylinositol glycan class A) gene recently were recognized as the cause of a clinically heterogeneous spectrum of X-linked disorders including (i) early onset epileptic encephalopathy with severe muscular hypotonia, dysmorphism, multiple congenital anomalies, and early death ("MCAHS2"), (ii) neurodegenerative encephalopathy with systemic iron overload (ferro-cerebro-cutaneous syndrome, "FCCS"), and (iii) intellectual disability and seizures without dysmorphism. Previous studies showed that the recurrent PIGA germline mutation c.1234C>T (p.Arg412*) leads to a clinical phenotype at the most severe end of the spectrum associated with early infantile lethality. We identified three additional individuals from two unrelated families with the same PIGA mutation. Major clinical findings include early onset intractable epileptic encephalopathy with a burst-suppression pattern on EEG, generalized muscular hypotonia, structural brain abnormalities, macrocephaly and increased birth weight, joint contractures, coarse facial features, widely spaced eyes, a short nose with anteverted nares, gingival overgrowth, a wide mouth, short limbs with short distal phalanges, and a small penis. Based on the phenotypic overlap with Simpson-Golabi-Behmel syndrome type 2 (SGBS2), we hypothesized that both disorders might have the same underlying cause. We were able to confirm the same c.1234C>T (p.Arg412*) mutation in the DNA sample from an affected fetus of the original family affected with SGBS2. We conclude that the recurrent PIGA germline mutation c.1234C>T leads to a recognizable clinical phenotype with a poor prognosis and is the cause of SGBS2.

N(8)-acetylspermidine as a potential plasma biomarker for Snyder-Robinson syndrome identified by clinical metabolomics.

Clinical metabolomics has emerged as a powerful tool to study human metabolism in health and disease. Comparative statistical analysis of untargeted metabolic profiles can reveal perturbations of metabolite levels in diseases and thus has the potential to identify novel biomarkers. Here we have applied a simultaneous genetic-metabolomic approach in twin boys with epileptic encephalopathy of unclear etiology. Clinical exome sequencing identified a novel missense mutation in the spermine synthase gene (SMS) that causes Snyder-Robinson syndrome (SRS). Untargeted plasma metabolome analysis revealed significantly elevated levels of N(8)-acetylspermidine, a precursor derivative of spermine biosynthesis, as a potential novel plasma biomarker for SRS. This result was verified in a third patient with genetically confirmed SRS. This study illustrates the potential of metabolomics as a translational technique to support exome data on a functional and clinical level.

APCDD1 is a novel Wnt inhibitor mutated in hereditary hypotrichosis simplex.

Hereditary hypotrichosis simplex is a rare autosomal dominant form of hair loss characterized by hair follicle miniaturization. Using genetic linkage analysis, we mapped a new locus for the disease to chromosome 18p11.22, and identified a mutation (Leu9Arg) in the adenomatosis polyposis down-regulated 1 (APCDD1) gene in three families. We show that APCDD1 is a membrane-bound glycoprotein that is abundantly expressed in human hair follicles, and can interact in vitro with WNT3A and LRP5-two essential components of Wnt signalling. Functional studies show that APCDD1 inhibits Wnt signalling in a cell-autonomous manner and functions upstream of beta-catenin. Moreover, APCDD1 represses activation of Wnt reporters and target genes, and inhibits the biological effects of Wnt signalling during both the generation of neurons from progenitors in the developing chick nervous system, and axis specification in Xenopus laevis embryos. The mutation Leu9Arg is located in the signal peptide of APCDD1, and perturbs its translational processing from the endoplasmic reticulum to the plasma membrane. APCDD1(L9R) probably functions in a dominant-negative manner to inhibit the stability and membrane localization of the wild-type protein. These findings describe a novel inhibitor of the Wnt signalling pathway with an essential role in human hair growth. As APCDD1 is expressed in a broad repertoire of cell types, our findings indicate that APCDD1 may regulate a diversity of biological processes controlled by Wnt signalling.

Variants in CUL4B are associated with cerebral malformations.

Variants in cullin 4B (CUL4B) are a known cause of syndromic X-linked intellectual disability. Here, we describe an additional 25 patients from 11 families with variants in CUL4B. We identified nine different novel variants in these families and confirmed the pathogenicity of all nontruncating variants. Neuroimaging data, available for 15 patients, showed the presence of cerebral malformations in ten patients. The cerebral anomalies comprised malformations of cortical development (MCD), ventriculomegaly, and diminished white matter volume. The phenotypic heterogeneity of the cerebral malformations might result from the involvement of CUL-4B in various cellular pathways essential for normal brain development. Accordingly, we show that CUL-4B interacts with WDR62, a protein in which variants were previously identified in patients with microcephaly and a wide range of MCD. This interaction might contribute to the development of cerebral malformations in patients with variants in CUL4B.

The clinical significance of small copy number variants in neurodevelopmental disorders.

BACKGROUND: Despite abundant evidence for pathogenicity of large copy number variants (CNVs) in neurodevelopmental disorders (NDDs), the individual significance of genome-wide rare CNVs <500 kb has not been well elucidated in a clinical context. METHODS: By high-resolution chromosomal microarray analysis, we investigated the clinical significance of all rare non-polymorphic exonic CNVs sizing 1-500 kb in a cohort of 714 patients with undiagnosed NDDs. RESULTS: We detected 96 rare CNVs <500 kb affecting coding regions, of which 58 (60.4%) were confirmed. 6 of 14 confirmed de novo, one of two homozygous and four heterozygous inherited CNVs affected the known microdeletion regions 17q21.31, 16p11.2 and 2p21 or OMIM morbid genes (CASK, CREBBP, PAFAH1B1, SATB2; AUTS2, NRXN3, GRM8). Two further de novo CNVs affecting single genes (MED13L, CTNND2) were instrumental in delineating novel recurrent conditions. For the first time, we here report exonic deletions of CTNND2 causing low normal IQ with learning difficulties with or without autism spectrum disorder. Additionally, we discovered a homozygous out-of-frame deletion of ACOT7 associated with features comparable to the published mouse model. In total, 24.1% of the confirmed small CNVs were categorised as pathogenic or likely pathogenic (median size 130 kb), 17.2% as likely benign, 3.4% represented incidental findings and 55.2% remained unclear. CONCLUSIONS: These results verify the diagnostic relevance of genome-wide rare CNVs <500 kb, which were found pathogenic in ∼2% (14/714) of cases (1.1% de novo, 0.3% homozygous, 0.6% inherited) and highlight their inherent potential for discovery of new conditions.

A new chromosome 17q21.31 microdeletion syndrome associated with a common inversion polymorphism.

Submicroscopic genomic copy number changes have been identified only recently as an important cause of mental retardation. We describe the detection of three interstitial, overlapping 17q21.31 microdeletions in a cohort of 1,200 mentally retarded individuals associated with a clearly recognizable clinical phenotype of mental retardation, hypotonia and a characteristic face. The deletions encompass the MAPT and CRHR1 genes and are associated with a common inversion polymorphism.

Infantile epileptic encephalopathy, transient choreoathetotic movements, and hypersomnia due to a De Novo missense mutation in the SCN2A gene.

Mutations of the SCN2A gene have originally been described in association with benign familial neonatal-infantile seizures (BFNIS). Recently, single patients with more severe phenotypes and persisting epileptic encephalopathies have been recognized. We report the case of a girl with severe infantile onset epileptic encephalopathy and a de novo missense mutation in the SCN2A gene (c.4025T > C/ = ; p.L1342P/ = ), who presented with a transient choreatic movement disorder, hypersomnia, and progressive brain atrophy. Whole exome sequencing did not reveal any other disease causing mutation. Our patient contributes to the expanding phenotypic spectrum of SCN2A-related disorders and underlines the importance of genetic workup in epileptic encephalopathies.

Microcephalic osteodysplastic primordial dwarfism type II (MOPD II) with multiple vascular complications misdiagnosed as Dubowitz syndrome.

UNLABELLED: To date, the genetic basis of Dubowitz syndrome (short stature, microcephaly, facial abnormalities, eczema) is unknown and vascular complications are not known to be associated with this syndrome. In microcephalic osteodysplastic primordial dwarfism type II (MOPD II; disproportionate short statue, microcephaly, facial abnormalities), however, cerebral aneurysms and other vascular abnormalities are frequent complications. MOPD II is a genetic disorder caused by mutations in the pericentrin (PCNT) gene (21q22). We report on a patient who came to our attention as a 22-year-old with subarachnoid bleeding due to a ruptured cranial aneurysm. Until then, the patient was thought and published to have Dubowitz syndrome; previously, he was treated with coronary bypass surgery for extensive coronary angiopathy. Consecutive genetic testing revealed MOPD II. After clinical stabilization, the patient was discharged to a specialized rehabilitation center where he died due to re-rupture of a cranial aneurysm. CONCLUSION: In patients with short stature-especially when clinical features are accompanied by vascular complications-MOPD II should be considered as a differential diagnosis leading to consecutive genetic testing. After detection of mutations in the PCNT gene, a full vascular status including cerebral imaging and cardiac evaluation needs to be determined in order to analyze vascular abnormalities and initiate prophylactic treatment.

High-resolution chromosomal microarrays in prenatal diagnosis significantly increase diagnostic power.

OBJECTIVE: The objective of this study was to determine for the first time the reliability and the diagnostic power of high-resolution microarray testing in routine prenatal diagnostics. METHODS: We applied high-resolution chromosomal microarray testing in 464 cytogenetically normal prenatal samples with any indication for invasive testing. RESULTS: High-resolution testing revealed a diagnostic yield of 6.9% and 1.6% in cases of fetal ultrasound anomalies and cases of advanced maternal age (AMA), respectively, which is similar to previous studies using low-resolution microarrays. In three (0.6%) additional cases with an indication of AMA, an aberration in susceptibility risk loci was detected. Moreover, one case (0.2%) showed an X-linked aberration in a female fetus, a finding relevant for future family planning. We found the rate of cases, in which the parents had to be tested for interpretation of unreported copy number variants (3.7%), and the rate of remaining variants of unknown significance (0.4%) acceptably low. Of note, these findings did not cause termination of pregnancy after expert genetic counseling. The 0.4% rate of confined placental mosaicism was similar to that observed by conventional karyotyping and notably involved a case of placental microdeletion. CONCLUSION: High-resolution prenatal microarray testing is a reliable technique that increases diagnostic yield by at least 17.3% when compared with conventional karyotyping, without an increase in the frequency of variants of uncertain significance.

Methylation profiling in individuals with uniparental disomy identifies novel differentially methylated regions on chromosome 15.

The maternal and paternal genomes possess distinct epigenetic marks that distinguish them at imprinted loci. In order to identify imprinted loci, we used a novel method, taking advantage of the fact that uniparental disomy (UPD) provides a system that allows the two parental chromosomes to be studied independently. We profiled the paternal and maternal methylation on chromosome 15 using immunoprecipitation of methylated DNA and hybridization to tiling oligonucleotide arrays. Comparison of six individuals with maternal versus paternal UPD15 revealed 12 differentially methylated regions (DMRs). Putative DMRs were validated by bisulfite sequencing, confirming the presence of parent-of-origin-specific methylation marks. We detected DMRs associated with known imprinted genes within the Prader-Willi/Angelman syndrome region, such as SNRPN and MAGEL2, validating this as a method of detecting imprinted loci. Of the 12 DMRs identified, eight were novel, some of which are associated with genes not previously thought to be imprinted. These include a site within intron 2 of IGF1R at 15q26.3, a gene that plays a fundamental role in growth, and an intergenic site upstream of GABRG3 that lies within a previously defined candidate region conferring an increased maternal risk of psychosis. These data provide a map of parent-of-origin-specific epigenetic modifications on chromosome 15, identifying DNA elements that may play a functional role in the imprinting process. Application of this methodology to other chromosomes for which UPD has been reported will allow the systematic identification of imprinted sites throughout the genome.

Further delineation of genotype-phenotype correlation in homozygous 2p21 deletion syndromes: first description of patients without cystinuria.

Homozygous contiguous gene deletion syndromes are rare. On 2p21, however, several overlapping homozygous gene deletion syndromes have been described, all presenting with cystinuria but otherwise distinct phenotypes. Hypotonia-cystinuria syndrome (HCS, OMIM606407) is characterized by infantile hypotonia, poor feeding, and growth hormone deficiency. Affected individuals carry homozygous deletions including the cystinuria gene SLC3A1 and the adjacent PREPL gene. Larger homozygous deletions in this region encompassing the PPM1B, SLC3A1, PREPL, and C2orf34 (CAMKMT) genes result in a more severe phenotype, the 2p21 deletion syndrome. A phenotype intermediate to HCS and the 2p21 deletion syndrome is termed atypical HCS and is caused by deletion of SLC3A1, PREPL, and C2orf34 (CAMKMT). Using high resolution SNP array molecular karyotyping we identified two siblings with a homozygous deletion of 83 kb partially encompassing the genes PREPL and C2orf34 (CAMKMT), but not the SLC3A1 gene. The affected siblings display a recognizable phenotype which is similar to atypical HCS with regard to growth failure and neuro-muscular features, but is characterized by lack of cystinuria. The patients also exhibit features which have not been reported to date such as cleft palate and genital abnormalities. In conclusion, we report the first patients with a homozygous 2p21 deletion syndrome without cystinuria and further delineate the complex genotype-phenotype correlations of homozygous microdeletion syndromes of this region.

Long-term follow-up of four patients with Langer-Giedion syndrome: clinical course and complications.

Long-term observations of individuals with the so-called Langer-Giedion (LGS) or tricho-rhino-phalangeal type II (TRPS2) are scarce. We report here a on follow-up of four LGS individuals, including one first described by Andres Giedion in 1969, and review the sparse publications on adults with this syndrome which comprises ectodermal dysplasia, multiple cone-shaped epiphyses prior to puberty, multiple cartilaginous exostoses, and mostly mild intellectual impairment. LGS is caused by deletion of the chromosomal segment 8q24.11-q24.13 containing among others the genes EXT1 and TRPS1. Most patients with TRPS2 are only borderline or mildly cognitively delayed, and few are of normal intelligence. Their practical skills are better than their intellectual capability, and, for this reason and because of their low self-esteem, they are often underestimated. Some patients develop seizures at variable age. Osteomas on processes of cervical vertebrae may cause pressure on cervical nerves or dissection of cerebral arteries. Joint stiffness is observed during childhood and changes later to joint laxity causing instability and proneness to trauma. Perthes disease is not rare. Almost all males become bald at or soon after puberty, and some develop (pseudo) gynecomastia. Growth hormone deficiency was found in a few patients, TSH deficiency so far only in one. Puberty and fertility are diminished, and no instance of transmission of the deletion from a non-mosaic parent to a child has been observed so far. Several affected females had vaginal atresia with consequent hydrometrocolpos.

The genetic landscape and clinical implication of pediatric Moyamoya angiopathy in an international cohort.

Pediatric Moyamoya Angiopathy (MMA) is a progressive intracranial occlusive arteriopathy that represents a leading cause of transient ischemic attacks and strokes in childhood. Despite this, up to now no large, exclusively pediatric MMA cohort has been subjected to systematic genetic investigation. In this study, we performed molecular karyotyping, exome sequencing and automated structural assessment of missense variants on a series of 88 pediatric MMA patients and correlated genetic, angiographic and clinical (stroke burden) findings. The two largest subgroups in our cohort consisted of RNF213 and neurofibromatosis type 1 (NF1) patients. While deleterious RNF213 variants were associated with a severe MMA clinical course with early symptom onset, frequent posterior cerebral artery involvement and higher stroke rates in multiple territories, NF1 patients had a similar infarct burden compared to non-NF1 individuals and were often diagnosed incidentally during routine MRIs. Additionally, we found that MMA-associated RNF213 variants have lower predicted functional impact compared to those associated with aortic disease. We also raise the question of MMA as a feature of recurrent as well as rare chromosomal imbalances and further support the possible association of MMA with STAT3 deficiency. In conclusion, we provide a comprehensive characterization at the genetic and clinical level of a large exclusively pediatric MMA population. Due to the clinical differences found across genetic subgroups, we propose genetic testing for risk stratification as part of the routine assessment of pediatric MMA patients.

First Report of a Low-Frequency Mosaic Mutation in the Hydroxymethylbilane Synthase Gene Causing Acute Intermittent Porphyria.

Acute porphyrias are a group of monogenetic inborn errors of heme biosynthesis, characterized by acute and potentially life-threatening neurovisceral attacks upon exposure to certain triggering factors. Biochemical analyses can determine the type of acute porphyria, and subsequent genetic analysis allows for the identification of pathogenic variants in the specific gene, which provides information for family counselling. In 2017, a male Swiss patient was diagnosed with an acute porphyria while suffering from an acute attack. The pattern of porphyrin metabolite excretion in urine, faeces, and plasma was typical for an acute intermittent porphyria (AIP), which is caused by inherited autosomal dominant mutations in the gene for hydroxymethylbilane synthase (HMBS), the third enzyme in the heme biosynthetic pathway. However, the measurement of HMBS enzymatic activity in the erythrocytes was within the normal range and Sanger sequencing of the HMBS gene failed to detect any pathogenic variants. To explore the molecular basis of the apparent AIP in this patient, we performed third-generation long-read single-molecule sequencing (nanopore sequencing) on a PCR product spanning the entire HMBS gene, including the intronic sequences. We identified a known pathogenic variant, c.77G>A, p.(Arg26His), in exon 3 at an allelic frequency of ~22% in the patient's blood. The absence of the pathogenic variant in the DNA of the parents and the results of additional confirmatory studies supported the presence of a de novo mosaic mutation. To our knowledge, such a mutation has not been previously described in any acute porphyria. Therefore, de novo mosaic mutations should be considered as potential causes of acute porphyrias when no pathogenic genetic variant can be identified through routine molecular diagnostics.

Identification of a novel loss-of-function calcium channel gene mutation in short QT syndrome (SQTS6).

AIMS: Short QT syndrome (SQTS) is a genetically determined ion-channel disorder, which may cause malignant tachyarrhythmias and sudden cardiac death. Thus far, mutations in five different genes encoding potassium and calcium channel subunits have been reported. We present, for the first time, a novel loss-of-function mutation coding for an L-type calcium channel subunit. METHODS AND RESULTS: The electrocardiogram of the affected member of a single family revealed a QT interval of 317 ms (QTc 329 ms) with tall, narrow, and symmetrical T-waves. Invasive electrophysiological testing showed short ventricular refractory periods and increased vulnerability to induce ventricular fibrillation. DNA screening of the patient identified no mutation in previously known SQTS genes; however, a new variant at a heterozygous state was identified in the CACNA2D1 gene (nucleotide c.2264G > C; amino acid p.Ser755Thr), coding for the Ca(v)α(2)δ-1 subunit of the L-type calcium channel. The pathogenic role of the p.Ser755Thr variant of the CACNA2D1 gene was analysed by using co-expression of the two other L-type calcium channel subunits, Ca(v)1.2α1 and Ca(v)ß(2b), in HEK-293 cells. Barium currents (I(Ba)) were recorded in these cells under voltage-clamp conditions using the whole-cell configuration. Co-expression of the p.Ser755Thr Ca(v)α(2)δ-1 subunit strongly reduced the I(Ba) by more than 70% when compared with the co-expression of the wild-type (WT) variant. Protein expression of the three subunits was verified by performing western blots of total lysates and cell membrane fractions of HEK-293 cells. The p.Ser755Thr variant of the Ca(v)α(2)δ-1 subunit was expressed at a similar level compared with the WT subunit in both fractions. Since the mutant Ca(v)α(2)δ-1 subunit did not modify the expression of the pore-forming subunit of the L-type calcium channel, Ca(v)1.2α1, it suggests that single channel biophysical properties of the L-type channel are altered by this variant. CONCLUSION: In the present study, we report the first pathogenic mutation in the CACNA2D1 gene in humans, which causes a new variant of SQTS. It remains to be determined whether mutations in this gene lead to other manifestations of the J-wave syndrome.

A Xp22.11-p21.3 microdeletion in a three-generation family supports male lethality of POLA1 nullisomy resulting in reduced fertility of female carriers.

POLA1 encodes a subunit of the DNA polymerase alpha, a key enzyme for the initiation of DNA synthesis. In males, hemizygous hypomorphic variants in POLA1 have been identified as the cause of X-linked pigmentary reticulate disorder (XLPDR) and a novel X-linked neurodevelopmental disorder termed Van Esch-O'Driscoll syndrome (VEODS), while female carriers have been reported to be healthy. Nullisomy for POLA1 was speculated to be lethal due to its crucial function, while the effect of loss of one allele in females remained unknown. Here, we report on a three-generation family harboring a deletion of POLA1 in females showing subfertility as the only phenotype. Our findings show that heterozygous deletions or truncating variants in females with skewed X inactivation do not cause VEODS and support the hypothesis of very early embryonic lethality in males with POLA1 nullisomy.