Heterotrimeric G proteins are immediate transducers of G protein-coupled receptors—the biggest receptor family in metazoans—and play innumerate functions in health and disease. A set of de novo point mutations in GNAO1 and GNAI1, the genes encoding the α-subunits (Gαo and Gαi1, respectively) of the heterotrimeric G proteins, have been described to cause pediatric encephalopathies represented by epileptic seizures, movement disorders, developmental delay, intellectual disability, and signs of neurodegeneration. Among such mutations, the Gln52Pro substitutions have been previously identified in GNAO1 and GNAI1. Here, we describe the case of an infant with another mutation in the same site, Gln52Arg. The patient manifested epileptic and movement disorders and a developmental delay, at the onset of 1.5 weeks after birth. We have analyzed biochemical and cellular properties of the three types of dominant pathogenic mutants in the Gln52 position described so far: Gαo[Gln52Pro], Gαi1[Gln52Pro], and the novel Gαo[Gln52Arg]. At the biochemical level, the three mutant proteins are deficient in binding and hydrolyzing GTP, which is the fundamental function of the healthy G proteins. At the cellular level, the mutants are defective in the interaction with partner proteins recognizing either the GDP-loaded or the GTP-loaded forms of Gαo. Further, of the two intracellular sites of Gαo localization, plasma membrane and Golgi, the former is strongly reduced for the mutant proteins. We conclude that the point mutations at Gln52 inactivate the Gαo and Gαi1 proteins leading to aberrant intracellular localization and partner protein interactions. These features likely lie at the core of the molecular etiology of pediatric encephalopathies associated with the codon 52 mutations in GNAO1/GNAI1.

GNE myopathy (GNEM) is a rare hereditary disease, but at the same time, it is the most common distal myopathy in several countries due to a founder effect of some pathogenic variants in the GNE gene. We collected the largest cohort of patients with GNEM from Russia and analyzed their mutational spectrum and clinical data. In our cohort, 10 novel variants were found, including 2 frameshift variants and 2 large deletions. One novel missense variant c.169_170delGCinsTT (p.(Ala57Phe)) was detected in 4 families in a homozygous state and in 3 unrelated patients in a compound heterozygous state. It was the second most frequent variant in our cohort. All families with this novel frequent variant were non-consanguineous and originated from the 3 neighboring areas in the European part of Russia. The clinical picture of the patients carrying this novel variant was typical, but the severity of clinical manifestation differed significantly. In our study, we reported two atypical cases expanding the phenotypic spectrum of GNEM. One female patient had severe quadriceps atrophy, hand joint contractures, keloid scars, and non-classical pattern on leg muscle magnetic resonance imaging, which was more similar to atypical collagenopathy rather than GNEM. Another patient initially had been observed with spinal muscular atrophy due to asymmetric atrophy of hand muscles and results of electromyography. The peculiar pattern of muscle involvement on magnetic resonance imaging consisted of pronounced changes in the posterior thigh muscle group with relatively spared muscles of the lower legs, apart from the soleus muscles. Different variants in the GNE gene were found in both atypical cases. Thus, our data expand the mutational and clinical spectrum of GNEM.

A timely detection of patients with tetrahydrobiopterin (BH₄) -deficient types of hyperphenylalaninemia (HPABH₄) is important for assignment of correct therapy, allowing to avoid complications. Often HPABH₄ patients receive the same therapy as phenylalanine hydroxylase (PAH) -deficiency (phenylketonuria) patients—dietary treatment—and do not receive substitutive BH₄ therapy until the diagnosis is confirmed by molecular genetic means. In this study, we present a cohort of 30 Russian patients with HPABH₄ with detected variants in genes causing different types of HPA. Family diagnostics and biochemical urinary pterin spectrum analyses were carried out. HPABH₄A is shown to be the prevalent type, 83.3% of all HPABH₄ cases. The mutation spectrum for the PTS gene was defined, the most common variants in Russia were p.Thr106Met—32%, p.Asn72Lys—20%, p.Arg9His—8%, p.Ser32Gly—6%. We also detected 7 novel PTS variants and 3 novel QDPR variants. HPABH₄ prevalence was estimated to be 0.5–0.9% of all HPA cases in Russia, which is significantly lower than in European countries on average, China, and Saudi Arabia. The results of this research show the necessity of introducing differential diagnostics for HPABH₄ into neonatal screening practice.

Heterozygous variants in RAR-related orphan receptor B (RORB) have recently been associated with susceptibility to idiopathic generalized epilepsy. However, few reports have been published so far describing pathogenic variants of this gene in patients with epilepsy and intellectual disability (ID). In this study, we aimed to delineate the epilepsy phenotype associated with RORB pathogenic variants and to provide arguments in favor of the pathogenicity of variants. Through an international collaboration, we analyzed seizure characteristics, EEG data, and genotypes of a cohort of patients with heterozygous variants in RORB. To gain insight into disease mechanisms, we performed ex vivo cortical electroporation in mouse embryos of 5 selected variants, 2 truncating and 3 missense, and evaluated on expression and quantified changes in axonal morphology. We identified 35 patients (17 male, median age 10 years, range 2.5-23 years) carrying 32 different heterozygous variants in RORB, including 28 single-nucleotide variants or small insertions/deletions (12 missense, 12 frameshift or nonsense, 2 splice-site variants, and 2 in-frame deletions), and 4 microdeletions; de novo in 18 patients and inherited in 10. Seizures were reported in 31/35 (89%) patients, with a median age at onset of 3 years (range 4 months-12 years). Absence seizures occurred in 25 patients with epilepsy (81%). Nineteen patients experienced a single seizure type: absences, myoclonic absences, or absences with eyelid myoclonia and focal seizures. Nine patients had absence seizures combined with other generalized seizure types. One patient had presented with absences associated with photosensitive occipital seizures. Three other patients had generalized tonic-clonic seizures without absences. ID of variable degree was observed in 85% of the patients. Expression studies in cultured neurons showed shorter axons for the 5 tested variants, both truncating and missense variants, supporting an impaired protein function. In most patients, the phenotype of the RORB-related disorder associates absence seizures with mild-to-moderate ID. In silico and in vitro evaluation of the variants in our cohort, including axonal morphogenetic experiments in cultured neurons, supports their pathogenicity, showing a hypomorphic effect.

A young boy with multifocal epilepsy with infantile spasms and hypsarrhythmia with minimal organic lesions of brain structures underwent DNA diagnosis using whole‐exome sequencing. A heterozygous amino‐acid substitution p.L519R in a PHACTR1 gene was identified. PHACTR1 belongs to a protein family of G‐actin binding protein phosphatase 1 (PP1) cofactors and was not previously associated with a human disease. The missense single nucleotide variant in the proband was shown to occur de novo in the paternal allele. The mutation was shown in vitro to reduce the affinity of PHACTR1 for G‐actin, and to increase its propensity to form complexes with the catalytic subunit of PP1. These properties are associated with altered subcellular localization of PHACTR1 and increased ability to induce cytoskeletal rearrangements. Although the molecular role of the PHACTR1 in neuronal excitability and differentiation remains to be defined, PHACTR1 has been previously shown to be involved in Slack channelopathy pathogenesis, consistent with our findings. We conclude that this activating mutation in PHACTR1 causes a severe type of sporadic multifocal epilepsy in the patient.