Expanding the genotype-phenotype spectrum in SCN8A-related disorders.

Background: SCN8A-related disorders are a group of variable conditions caused by pathogenic variations in SCN8A. Online Mendelian Inheritance in Man (OMIM) terms them as developmental and epileptic encephalopathy 13, benign familial infantile seizures 5 or cognitive impairment with or without cerebellar ataxia.

Methods: In this study, we describe clinical and genetic results on eight individuals from six families with SCN8A pathogenic variants identified via exome sequencing.

Mechanisms of mRNA processing defects in inherited intellectual disability syndrome.

is the genetic basis of autosomal recessive THOC6 Intellectual Disability Syndrome (TIDS). THOC6 facilitates the formation of the Transcription Export complex (TREX) tetramer, composed of four THO monomers. The TREX tetramer supports mammalian mRNA processing that is distinct from yeast TREX dimer functions.

Expanding the genotype-phenotype spectrum in SCN8A-related disorders.

Background: -related disorders are a group of variable conditions caused by pathogenic variations in . Online Mendelian Inheritance in Man (OMIM) terms them as developmental and epileptic encephalopathy 13, benign familial infantile seizures 5 or cognitive impairment with or without cerebellar ataxia.

Methods: In this study, we describe clinical and genetic results on eight individuals from six families with pathogenic variants identified via exome sequencing.

Clinical and genetic spectrum of 104 Indian families with central nervous system white matter abnormalities.

Genetic disorders with predominant central nervous system white matter abnormalities (CNS WMAs), also called leukodystrophies, are heterogeneous entities. We ascertained 117 individuals with CNS WMAs from 104 unrelated families. Targeted genetic testing was carried out in 16 families and 13 of them received a diagnosis.

Biallelic start loss variant, c.1A > G in GCSH is associated with variant nonketotic hyperglycinemia.

The glycine cleavage system H protein (GCSH) is an integral part of the glycine cleavage system with its additional involvement in the synthesis and transport of lipoic acid. We hypothesize that pathogenic variants in GCSH can cause variant nonketotic hyperglycinemia (NKH), a heterogeneous group of disorders with findings resembling a combination of severe NKH (elevated levels of glycine in plasma and CSF, progressive lethargy, seizures, severe hypotonia, no developmental progress, early death) and mitochondriopathies (lactic acidosis, leukoencephalopathy and Leigh-like lesions on MRI). We herein report three individuals from two unrelated Indian families with clinical, biochemical, and radiological findings of variant NKH, harboring a biallelic start loss variant, c.

Recent advances in epilepsy genomics and genetic testing.

Developmental and epileptic encephalopathies (DEEs) are a group of severe, early onset epilepsies characterized by refractory seizures, developmental delay or regression associated with ongoing epileptic activity, and generally poor prognosis. DEE is genetically and phenotypically heterogeneous, and there is a plethora of genetic testing options to investigate the rapidly growing list of epilepsy genes. However, more than 50% of patients with DEE remain without a genetic diagnosis despite state-of-the-art genetic testing.

Locus and allelic heterogeneity in five families with hereditary spastic paraplegia.

Hereditary spastic paraplegias are a group of genetically heterogeneous neurological disorders characterized by progressive weakness and spasticity of lower limbs. We ascertained five families with eight individuals with hereditary spastic paraplegia. Pathogenic variants were identified by exome sequencing of index cases.

Bi-allelic c.181_183delTGT in BTB domain of KLHL7 is associated with overlapping phenotypes of Crisponi/CISS1-like and Bohring-Opitz like syndrome.

Biallelic pathogenic variants in KLHL7 are known to result in Crisponi syndrome (CS)/cold-induced sweating syndrome type 1 (CISS1) like phenotype and Bohring-Opitz-like syndrome. In this report, a trio whole-exome sequencing (WES) was performed in proband with cold-induced sweating, microcephaly, facial dysmorphism, spasticity, failure to thrive, pigmentary abnormalities of the retina, hypoplasia of corpus callosum and periventricular nodular heterotopia. A novel homozygous in-frame deletion was identified in exon 2 of KLHL7, affecting the BTB domain of the protein.

Genetic diversity of NDUFV1-dependent mitochondrial complex I deficiency.

Medical genomics research performed in diverse population facilitates a better understanding of the genetic basis of developmental disorders, with regional implications for community genetics. Autosomal recessive mitochondrial complex I deficiency (MCID) accounts for a constellation of clinical features, including encephalopathies, myopathies, and Leigh Syndrome. Using whole-exome sequencing, we identified biallelic missense variants in NDUFV1 that encodes the 51-kD subunit of complex I (NADH dehydrogenase) NDUFV1.

A biallelic 36-bp insertion in PIBF1 is associated with Joubert syndrome.

Biallelic pathogenic variants in PIBF1 have been identified as one of the genetic etiologies of Joubert syndrome. We report a two-year-old girl with global developmental delay, facial dysmorphism, hypotonia, enlarged cystic kidneys, molar tooth sign, and thinning of corpus callosum. A novel homozygous 36-bp insertion in PIBF1 (c.

A neurodegenerative mitochondrial disease phenotype due to biallelic loss-of-function variants in PNPLA8 encoding calcium-independent phospholipase A2γ.

Animal studies have demonstrated the critical roles of the patatin-like protein family plays in cellular growth, lipid homeostasis, and second messenger signaling the nervous system. Of the nine known calcium-independent phospholipase A2γ, only PNPLA2, PNLPA6, PNPLA9 and most recently a single patient with PNPLA8 are associated with mitochondrial-related neurodegeneration. Using whole exome sequencing, we report two unrelated individuals with variable but similar clinical features of microcephaly, severe global developmental delay, spasticity, lactic acidosis, and progressive cerebellar atrophy with biallelic loss-of-function variants in PNPLA8.

Clinical and genetic spectrum of AMPD2-related pontocerebellar hypoplasia type 9.

Pontocerebellar hypoplasia (PCH) represents a group of autosomal-recessive progressive neurodegenerative disorders of prenatal onset. Eleven PCH subtypes are classified according to clinical, neuroimaging and genetic findings. Individuals with PCH type 9 (PCH9) have a unique combination of postnatal microcephaly, hypoplastic cerebellum and pons, and hypoplastic or absent corpus callosum.

Homozygosity for a nonsense variant in AIMP2 is associated with a progressive neurodevelopmental disorder with microcephaly, seizures, and spastic quadriparesis.

We ascertained two unrelated consanguineous families with two affected children each having microcephaly, refractory seizures, intellectual disability, and spastic quadriparesis. Magnetic resonance imaging showed atrophy of cerebrum, cerebellum and spinal cord, prominent cisterna magna, symmetric T2 hypo-intensities in the bilateral basal ganglia and thinning of corpus callosum. Whole-exome sequencing of three affected individuals revealed c.

p.Arg69Trp in RNASEH2C is a founder variant in three Indian families with Aicardi-Goutières syndrome.

Aicardi-Goutières syndrome is an early-onset severe neurological disorder characterized by intracranial calcification, white matter abnormalities, hepatosplenomegaly, cerebrospinal fluid lymphocytosis, and elevated interferon-α levels, thus mimicking congenital viral infections. It is a genetically heterogeneous condition and autosomal recessive and autosomal dominant forms with variations in seven genes known till date. Variations in RNASEH2C cause an autosomal recessive form of AGS.

Hyperphosphatasia with Mental Retardation Syndrome Due to a Novel Mutation in .

Hyperphosphatasia with mental retardation syndrome is a heterogeneous genetic condition. Two siblings aged 5 years and 3 years were evaluated for global development delay and facial dysmorphism. A novel missense variant, c.

Homozygous c.359del variant in MGME1 is associated with early onset cerebellar ataxia.

We ascertained a child with early onset cerebellar ataxia and identified a novel frameshift deletion, c.359del [p. (Pro120Leufs*2), NM_052865.

Homozygous p.(Glu87Lys) variant in ISCA1 is associated with a multiple mitochondrial dysfunctions syndrome.

The iron-sulfur (Fe-S) cluster (ISC) biogenesis pathway is indispensable for many fundamental biological processes and pathogenic variations in genes encoding several components of the Fe-S biogenesis machinery, such as NFU1, BOLA3, IBA57 and ISCA2 are already implicated in causing four types of multiple mitochondrial dysfunctions syndromes (MMDS). We report on two unrelated families, with two affected children each with early onset neurological deterioration, seizures, extensive white matter abnormalities, cortical migrational abnormalities, lactic acidosis and early demise. Exome sequencing of two affected individuals, one from each family, revealed a homozygous c.

Biallelic Loss of Proprioception-Related PIEZO2 Causes Muscular Atrophy with Perinatal Respiratory Distress, Arthrogryposis, and Scoliosis.

We report ten individuals of four independent consanguineous families from Turkey, India, Libya, and Pakistan with a variable clinical phenotype that comprises arthrogryposis, spontaneously resolving respiratory insufficiency at birth, muscular atrophy predominantly of the distal lower limbs, scoliosis, and mild distal sensory involvement. Using whole-exome sequencing, SNPchip-based linkage analysis, DNA microarray, and Sanger sequencing, we identified three independent homozygous frameshift mutations and a homozygous deletion of two exons in PIEZO2 that segregated in all affected individuals of the respective family. The mutations are localized in the N-terminal and central region of the gene, leading to nonsense-mediated transcript decay and consequently to lack of PIEZO2 protein.