Biallelic pathogenic variants in PNKP are associated with microcephaly and early-onset seizures (MCSZ), ataxia with oculomotor apraxia type 4 and Charcot-Marie-Tooth disease type 2B2. We describe the clinical and neuroimaging features of 27 new patients with PNKP variants. All patients presented with early-onset seizures, congenital microcephaly and intellectual disability. In addition, we compared our results with data in the literature. Twenty-five patients presented with the classic MCSZ phenotype, while two showed a more severe clinical phenotype. The brain imaging features of the 25 patients varied significantly, but widening of the frontal lobe gyri with frontal hypoplasia and prominent cerebellar folia (consistent with atrophy) could point to PNKP-related microcephaly . In contrast, the two patients with severe phenotype showed additional brain MRI features of white matter loss and pontocerebellar hypoplasia fulfilling the criteria of microlissencephaly. Exome sequencing identified seven different PNKP variants, including two novel ones. The c.1253_1269dup p.(Thr424GlyfsTer49) and c.1381_1383dup p.(Asn461dup) variants, each was recurrent in 10 patients (37%), while the c.1381_1383del p.(Asn461del) variant was recurrent in four patients (14.8%). Haplotype analysis confirmed that the p.Asn461dup variant has a founder effect in our population. No genotype-phenotype correlation was observed in our cohort. Our results provide 'microlissencephaly' as an emerging distinct phenotype linked to PNKP variants. As such, PNKP variants could be associated with four overlapping subgroups that lie along a unifying phenotypic continuum.

Pontocerebellar hypoplasia (PCH) represents a group of disorders characterized by cerebellum and pons hypoplasia, variable cerebral involvement, microcephaly, severe global developmental delay (GDD), and seizures. We sought the genetic cause of PCH in two siblings. Genetic workup was performed by whole-exome sequencing followed by Sanger validation. Morpholino-knockdown zebrafish embryos with human wild-type gene rescue were used to assess cerebellar development and motor function. Transfected mouse hippocampal cultures and electroporated mouse embryos were employed to assess functional effects on neuronal morphology and development. Both patients presented with profound GDD, severe microcephaly, cataracts, and variably seizures. Their MRIs demonstrated marked cerebellar and pontine hypoplasia. Both were homozygous for a c.416T > C, p.(Leu139Pro) MED29 variant which was predicted to be pathogenic. Locomotion and cerebellar GABAergic neurons development were both impaired in MED29 Morpholino-knockdown zebrafish and rescued by human wild-type gene expression. ShRNA-knockdown of MED29 in mouse hippocampal neurons decreased neurite length and arborization in vitro, and caused defective embryonic neuronal migration in vivo. Overexpression of MED29 p.(Leu139Pro) was consistent with a loss-of-function. Taken together, the Mediator complex regulates transcription processes, and defects in particular subunits are associated with distinct neurodevelopmental phenotypes involving PCH. We conclude that MED29 is a novel risk gene for PCH.

Objective: Vaccinia-related kinase 1 (VRK1)-related disease is an extremely rare autosomal recessive disorder primarily affecting the peripheral and/or central nervous system. In this report, we describe the genetic and clinical features of two siblings from a Turkish family presenting with an amyotrophic lateral sclerosis (ALS) phenotype due to a novel homozygous VRK1 mutation, and discuss the broad phenotypic spectrum associated with pathogenic variants in this gene. Methods: We analyzed the demographic data, clinical histories, neurological examinations, laboratory findings, and genetic results of 53 patients, including our cases, derived from 27 different reports. Results: Whole-exome sequencing identified a novel homozygous missense mutation, c.700A > G (p.Asn234Asp), in the VRK1 gene in two affected siblings. The characteristic features of the ALS phenotype included a recessive inheritance pattern, motor deficits with onset in the lower limbs, pyramidal tract signs, and a muscle magnetic resonance imaging (MRI) pattern demonstrating preferential involvement of the posterior compartments of the leg and thigh. The most common phenotypes associated with VRK1 mutations were ALS (18/53, 34%) and distal hereditary motor neuropathy (dHMN) (14/53, 26.4%), followed by pontocerebellar hypoplasia type 1 (7/53, 13.2%), hereditary motor and sensory neuropathy (5/53, 9.4%), autosomal recessive primary microcephaly with brain malformations (4/53, 7.5%), and spastic paraplegia (2/53, 3.8%). The ALS phenotype exhibited a significantly earlier mean age of onset compared to the dHMN phenotype (p = 0.015; 15.3 ± 11.5 and 27 ± 15.5 years, respectively). Conclusion: Our findings highlight the importance of investigating VRK1 mutations in patients with young-onset familial ALS. Furthermore, this report provides a systematic classification of the phenotype definitions associated with VRK1 mutations.

Maple Syrup Urine Disease (MSUD, OMIM# 248600) is an autosomal recessive inborn error of metabolism characterized by elevated branched chain amino acids (BCAA) leucine/isoleucine and valine in blood of affected children. The phenotypic and genotypic spectrum of MSUD is largely unreported in Egypt. We recruited ten patients (4 males/6 females, 2weeks-12years) from nine unrelated families with clinical and biochemical evidence of MSUD. We performed Sanger sequencing for the three most-commonly responsible genes: BCKDHA, BCKDHB and DBT and conducted exome sequencing for unresolved cases. Through Sanger sequencing, we detected eight homozygous pathogenic/likely pathogenic variants (four in BCKDHB, three in BCKDHA and one in DBT gene) in eight different families. The proband of family VI, who had no significant genetic findings by Sanger, had a peculiar phenotype and atypical radiological findings. His exome sequencing revealed a previously reported homozygous likely pathogenic variant in the RARS2 gene (NM_020320.5:c.1026G > A;p.(Met342Ile)) causing the mitochondrial-encephalopathy disorder pontocerebellar hypoplasia, type 6 (OMIM# 611523). Furthermore, the copy-number-variant analysis of the exome data revealed a biallelic duplication affecting exons 2-6 of the BCKDHB gene (GRCh38: Chr.6-g.80127496:80171441dup) evaluated as variant of uncertain significance but expected to cause a breakpoint and may disrupt gene function, which can explain the markedly elevated BCAA levels in the patient's blood. In conclusion, we expanded the genotypic and phenotypic spectrum of the disease and showed that aggressive intervention with specific treatment in the first few days of life resulted in normal development even in a developing country setting. Inclusion of MSUD in the national newborn screening program in Egypt is highly recommended.

To describe the MR features enabling prenatal diagnosis of pontocerebellar hypoplasia (PCH). This was a retrospective single monocentre study. The inclusion criteria were decreased cerebellar biometry on dedicated neurosonography and available fetal Magnetic Resonance Imaging (MRI) with PCH diagnosis later confirmed either genetically or clinically on post-natal MRI or by autopsy. The exclusion criteria were non-available MRI and sonographic features suggestive of a known genetic or other pathologic diagnosis. The collected data were biometric or morphological imaging parameters, clinical outcome, termination of pregnancy (TOP), pathological findings and genetic analysis (karyotyping, chromosomal microarray, DNA sequencing targeted or exome). PCH was classified as classic, non-classic, chromosomal, or unknown type. Forty-two fetuses were diagnosed with PCH, of which 27 were referred for decreased transverse cerebellar diameter at screening ultrasound. Neurosonography and fetal MRI were performed at a mean gestational age of 29 + 4 and 31 + 0 weeks, respectively. Termination of pregnancy occurred. Pregnancy was terminated in 24 cases. Neuropathological examination confirmed the diagnosis in 24 cases and genetic testing identified abnormalities in 29 cases (28 families, 14 chromosomal anomaly). Classic PCH is associated with pontine atrophy and small MR measurements decreasing with advancing gestation. This is the first large series of prenatally diagnosed PCHs. Our study shows the essential contribution of fetal MRI to the prenatal diagnosis of PCH. Classic PCHs are particularly severe and are associated with certain MR features.