Neurodevelopmental and Epilepsy Phenotypes in Individuals With Missense Variants in the Voltage-Sensing and Pore Domains of KCNH5.

BACKGROUND AND OBJECTIVES: KCNH5 encodes the voltage-gated potassium channel EAG2/Kv10.2. We aimed to delineate the neurodevelopmental and epilepsy phenotypic spectrum associated with de novo KCNH5 variants. METHODS: We screened 893 individuals with developmental and epileptic encephalopathies for KCNH5 variants using targeted or exome sequencing. Additional individuals with KCNH5 variants were identified through an international collaboration. Clinical history, EEG, and imaging data were analyzed; seizure types and epilepsy syndromes were classified. We included 3 previously published individuals including additional phenotypic details. RESULTS: We report a cohort of 17 patients, including 9 with a recurrent de novo missense variant p.Arg327His, 4 with a recurrent missense variant p.Arg333His, and 4 additional novel missense variants. All variants were located in or near the functionally critical voltage-sensing or pore domains, absent in the general population, and classified as pathogenic or likely pathogenic using the American College of Medical Genetics and Genomics criteria. All individuals presented with epilepsy with a median seizure onset at 6 months. They had a wide range of seizure types, including focal and generalized seizures. Cognitive outcomes ranged from normal intellect to profound impairment. Individuals with the recurrent p.Arg333His variant had a self-limited drug-responsive focal or generalized epilepsy and normal intellect, whereas the recurrent p.Arg327His variant was associated with infantile-onset DEE. Two individuals with variants in the pore domain were more severely affected, with a neonatal-onset movement disorder, early-infantile DEE, profound disability, and childhood death. DISCUSSION: We describe a cohort of 17 individuals with pathogenic or likely pathogenic missense variants in the voltage-sensing and pore domains of Kv10.2, including 14 previously unreported individuals. We present evidence for a putative emerging genotype-phenotype correlation with a spectrum of epilepsy and cognitive outcomes. Overall, we expand the role of EAG proteins in human disease and establish KCNH5 as implicated in a spectrum of neurodevelopmental disorders and epilepsy.

The Genetic Landscape and Epidemiology of Phenylketonuria.

Phenylketonuria (PKU), caused by variants in the phenylalanine hydroxylase (PAH) gene, is the most common autosomal-recessive Mendelian phenotype of amino acid metabolism. We estimated that globally 0.45 million individuals have PKU, with global prevalence 1:23,930 live births (range 1:4,500 [Italy]-1:125,000 [Japan]). Comparing genotypes and metabolic phenotypes from 16,092 affected subjects revealed differences in disease severity in 51 countries from 17 world regions, with the global phenotype distribution of 62% classic PKU, 22% mild PKU, and 16% mild hyperphenylalaninemia. A gradient in genotype and phenotype distribution exists across Europe, from classic PKU in the east to mild PKU in the southwest and mild hyperphenylalaninemia in the south. The c.1241A>G (p.Tyr414Cys)-associated genotype can be traced from Northern to Western Europe, from Sweden via Norway, to Denmark, to the Netherlands. The frequency of classic PKU increases from Europe (56%) via Middle East (71%) to Australia (80%). Of 758 PAH variants, c.1222C>T (p.Arg408Trp) (22.2%), c.1066-11G>A (IVS10-11G>A) (6.4%), and c.782G>A (p.Arg261Gln) (5.5%) were most common and responsible for two prevalent genotypes: p.[Arg408Trp];[Arg408Trp] (11.4%) and c.[1066-11G>A];[1066-11G>A] (2.6%). Most genotypes (73%) were compound heterozygous, 27% were homozygous, and 55% of 3,659 different genotypes occurred in only a single individual. PAH variants were scored using an allelic phenotype value and correlated with pre-treatment blood phenylalanine concentrations (n = 6,115) and tetrahydrobiopterin loading test results (n = 4,381), enabling prediction of both a genotype-based phenotype (88%) and tetrahydrobiopterin responsiveness (83%). This study shows that large genotype databases enable accurate phenotype prediction, allowing appropriate targeting of therapies to optimize clinical outcome.

High dose genistein aglycone therapy is safe in patients with mucopolysaccharidoses involving the central nervous system.

Genistein (4,5,7-trihydroexyisoflavone), a soy derived isoflavone, has been proposed as a substrate reduction therapy in patients with mucopolysaccharidoses (MPS) disorders with central nervous system involvement based on studies in cultured fibroblasts demonstrating that this agent inhibits glycosaminoglycan synthesis. Several studies have reported treatment of MPS III patients with low dose genistein (5-15mg/kg/day) with no serious adverse effects and variable neurocognitive outcomes. Mice with MPS IIIB treated with high dose (160mg/kg/day) genistein exhibited a significant decrease in heparan sulfate accumulation and neuroinflammation in the brain and improvement of the behavioral phenotype. No study to date has been performed using high dose genistein treatment in MPS patients. We initiated an open label study to assess the safety of high dose genistein treatment in MPS patients with neurological impairment. Twenty-two eligible patients were treated at least 12months with pure synthetic genistein at a dose of 150mg/kg/day. Safety labs, urine GAG levels, clinical status and history of adverse events were obtained every 3months and physical examination was performed by single examiner at least every 12months. While neurocognitive level was not a primary endpoint, participants were asked to obtain annual neurocognitive testing if available and a 9 point disability scale (FPSS) was recorded at each study visit. In the course of 12months of treatment, we observed no serious adverse events that were unexplained by the underlying condition and no severe adverse events that were felt to be potentially related to the genistein therapy. Two male subjects developed Tanner II breast development not present at baseline which could be related to the mild estrogenic effects of genistein. We observed no consistent decline in urine GAG levels; however, urinary GAG excretion was erratic. After 12months, the FPSS remained unchanged in 16 patients and declined by 1 point in 2 patients. Based on the results obtained so far, high dose oral genistein therapy appears to be safe in MPS patients and additional testing in a larger randomized placebo controlled trial is needed to further assess safety and efficacy.

CDKL5 and ARX mutations in males with early-onset epilepsy.

Mutations in CDKL5 and ARX are known causes of early-onset epilepsy and severe developmental delay in males and females. Although numerous males with ARX mutations associated with various phenotypes have been reported in the literature, the majority of CDKL5 mutations have been identified in females with a phenotype characterized by early-onset epilepsy, severe global developmental delay, absent speech, and stereotypic hand movements. To date, only 10 males with CDKL5 mutations have been reported. Our retrospective study reports on the clinical, neuroimaging, and molecular findings of 18 males with early-onset epilepsy caused by either CDKL5 or ARX mutations. These 18 patients include eight new males with CDKL5 mutations and 10 with ARX mutations identified through sequence analysis of 266 and 346 males, respectively, at our molecular diagnostic laboratory. Our large dataset therefore expands on the number of reported males with CDKL5 mutations and highlights that aberrations of CDKL5 and ARX combined are an important consideration in the genetic forms of early-onset epilepsy in boys.

Home infusion therapy is safe and enhances compliance in patients with mucopolysaccharidoses.

The transition to home infusion therapy is described in 11 patients with mucopolysaccharide (MPS) disorders initially treated with enzyme replacement therapy (ERT) in an out-patient infusion center. Home therapy was well tolerated with no infusion-related reactions (IRR) occurring in 671 patient-weeks of treatment. In addition, compliance with the weekly treatment regimen was improved in patients on home therapy.