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Epilepsy is one of the most frequent neurological diseases, with focal epilepsy accounting for the largest number of cases. The genetic alterations involved in focal epilepsy are far from being fully elucidated.Here, we show that defective lipid signalling caused by heterozygous ultra-rare variants in PIK3C2B, encoding for the class II phosphatidylinositol 3-kinase PI3K-C2β, underlie focal epilepsy in humans. We demonstrate that patients’ variants act as loss-of-function alleles, leading to impaired synthesis of the rare signalling lipid phosphatidylinositol 3,4-bisphosphate, resulting in mTORC1 hyperactivation. In vivo, mutant Pik3c2b alleles caused dose-dependent neuronal hyperexcitability and increased seizure susceptibility, indicating haploinsufficiency as a key driver of disease. Moreover, acute mTORC1 inhibition in mutant mice prevented experimentally induced seizures, providing a potential therapeutic option for a selective group of patients with focal epilepsy.Our findings reveal an unexpected role for class II PI3K-mediated lipid signalling in regulating mTORC1-dependent neuronal excitability in mice and humans.

We describe a case of epileptic encephalopathy in a young woman with undiagnosed medium-chain acyl-coenzyme A dehydrogenase deficiency (MCADD), who presented with an early-onset focal motor status epilepticus (SE) then followed by permanent left hemiplegia and drug-resistant epilepsy with neurodevelopmental delay. Throughout her clinical history, recurrent episodes of lethargy, feeding difficulties, and clustering seizures occurred, progressing into a super refractory SE and death at the age of 25 years. Although epilepsy is not a distinctive feature of MCADD, we advise considering this metabolic disease as a possible etiology of epileptic encephalopathy and hemiconvulsion-hemiplegia-epilepsy syndrome of unknown origin, on the chance to provide a timely and targeted treatment preventing development delay and evolution to SE. Adult patients with epilepsy of unknown etiology not screened at birth for inborn errors of metabolism, such as MCADD, should be promptly investigated for these treatable conditions.

Bernard-Soulier syndrome (BSS) is an autosomal-recessive bleeding disorder caused by biallelic variants in the GP1BA, GP1BB, and GP9 genes encoding the subunits GPIbα, GPIbβ, and GPIX of the GPIb-IX complex. Pathogenic variants usually affect the extracellular or transmembrane domains of the receptor subunits. We investigated a family with BSS caused by the homozygous c.528_550del (p.Arg177Serfs*124) variant in GP1BB, which is the first mutation ever identified that affects the cytoplasmic domain of GPIbβ. The loss of the intracytoplasmic tail of GPIbβ results in a mild form of BSS, characterized by only a moderate reduction of the GPIb-IX complex expression and mild or absent bleeding tendency. The variant induces a decrease of the total platelet expression of GPIbβ, however, all of the mutant subunit expressed in platelets is correctly assembled into the GPIb-IX complex in the plasma membrane, indicating that the cytoplasmic domain of GPIbβ is not involved in assembly and trafficking of the GPIb-IX receptor. Finally, the c.528_550del mutation exerts a dominant effect and causes mild macrothrombocytopenia in heterozygous individuals, as also demonstrated by the investigation of a second unrelated pedigree. The study of this novel GP1BB variant provides new information on pathophysiology of BSS and the assembly mechanisms of the GPIb-IX receptor.

The inherited thrombocytopenias (IT) are a heterogeneous group of diseases resulting from mutations in more than 30 different genes. Among them, ACTN1-related thrombocytopenia (ACTN1-RT; Online Mendelian Inheritance in Man: 615193) is one of the most recently identified forms. It has been described as a mild autosomal dominant macrothrombocytopenia caused by mutations in ACTN1, a gene encoding for one of the two non-muscle isoforms of alpha-actinin. We recently identified seven new unrelated families with ACTN1-RT caused by different mutations. Two of them are novel missense variants (p.Trp128Cys and p.Pro233Leu), whose pathogenic role has been confirmed by in vitro studies. Together with the 10 families we have previously described, our cohort of ACTN1-RT now consists of 49 individuals carrying ACTN1 mutations. This is the largest case series ever collected and enabled a critical evaluation of the clinical aspects of the disease. We concluded that ACTN1-RT is the fourth most frequent form of IT worldwide and it is characterized by platelet macrocytosis in all affected subjects and mild thrombocytopenia in less than 80% of cases. The risk of bleeding, either spontaneous or upon haemostatic challenge, is negligible and there are no other associated defects, either congenital or acquired. Therefore, ACTN1-RT is a benign form of IT, whose diagnosis provides affected individuals and their families with a good prognosis.

MYH9-assoziierte Erkrankung (MYH9-RD) ist eine autosomal-dominante Thrombozytopenie, die durch Mutationen im Gen für die Nicht-Muskel-Myosin schwere Kette IIA (NMMHC-IIA) verursacht wird. Die Patienten weisen eine kongenitale Makrothrombozytopenie und Einschlüsse von NMMHC-IIA in Leukozyten auf und haben ein variables Risiko, Nierenschäden, sensorineurale Taubheit, präsenile Katarakte und / oder Leberenzyme zu entwickeln. Das Spektrum der bei MYH9-RD-Patienten gefundenen Mutationen ist begrenzt und die Inzidenz und der Schweregrad der nicht-kongenitalen Merkmale werden durch die verursachende MYH9-Variante prognostiziert. Insbesondere assoziieren verschiedene Veränderungen der C-terminalen Schwanzdomäne von NMMHC-IIA mit einer bemerkenswert unterschiedlichen Krankheitsentwicklung. Wir berichten über vier neue MYH9-Mutationen, die die Schwanzdomäne von NMMHC-IIA betreffen und in vier Familien für MYH9-RD verantwortlich sind. Zwei Varianten verursachen Aminosäuresubstitutionen in der Coiled-Coil-Region von NMMHC-IIA, während die anderen beiden eine Splicing-Variante und eine Einzelnucleotid-Deletion sind, die beide zu Frameshift-Veränderungen des kurzen nicht-helikalen Schwanzstückes führen. Die Charakterisierung der Phänotypen betroffener Individuen zeigt, dass alle diese neuen Varianten mit einer milden klinischen Entwicklung der Erkrankung einhergehen.

Thrombopoietin (THPO) is an essential regulator of haemopoiesis that is required for the maintenance of haemopoietic progenitors and their differentiation into megakaryocytes (Mks). Moreover, it modulates the events that drive Mk maturation and allows the release of platelets into bone marrow sinusoids. THPO plays these roles by binding the MPL receptor, which is expressed in bone marrow stem cells, Mks, platelets and many other human cells. Until recently, no inherited THPO defect was known to cause thrombocytopenia or bone marrow aplasia. However, it was recently shown that microdeletions encompassing the THPO gene in chromosome 3 result in a complex clinical picture, including mild congenital thrombocytopenia. Moreover, a Micronesian family carrying the homozygous c.112C>T (p.Arg38Cys or p.Arg17Cys in the mature protein) missense mutation in THPO presents inherited bone marrow aplasia. No THPO mutation associated with isolated thrombocytopenia has been reported to date, but the application of whole exome sequencing (WES) in a cohort of patients with inherited thrombocytopenias (ITs) of unknown origin revealed that monoallelic changes in this gene identify a new form of IT. In fact, WES identified two unrelated individuals carrying the heterozygous variant c.91C>T (p. Arg31*), which is expected to result in mutant protein degradation and THPO haploinsufficiency.

The increased risk for autosomal recessive disorders is one of the most well-known medical implications of consanguinity. In the Sultanate of Oman, a country characterized by one of the highest rates of consanguineous marriages worldwide, prevalence of genetic hearing loss (GHL) is estimated to be 6/10 000. Families of GHL patients have higher consanguinity rates than the general Omani population, indicating a major role for recessive forms. Mutations in GJB2, the most commonly mutated GHL gene, have been sporadically described. We collected 97 DNA samples of GHL probands, affected/unaffected siblings and parents from 26 Omani consanguineous families. Analyzing a first family by whole-exome sequencing, we identified a novel homozygous frameshift duplication (c.1171_1177dupGCCATCT) in MYO15A, the gene linked to the deafness locus DFNB3. This duplication was then found in a total of 8/26 (28%) families, within a 849 kb founder haplotype. Reconstruction of haplotype structure at MYO15A surrounding genomic regions indicated that the founder haplotype branched out in the past two to three centuries from a haplotype present worldwide. The MYO15A duplication emerges as the major cause of GHL in Oman. These findings have major implications for the design of GHL diagnosis and prevention policies in Oman.