Novel SLC30A2 mutations in the pathogenesis of transient neonatal zinc deficiency.

Importance: Transient neonatal zinc deficiency (TNZD) occurs in breastfed infants due to abnormally low breast milk zinc levels. Mutations in the solute carrier family 30 member 2 (SLC30A2) gene, which encodes the zinc transporter ZNT2, cause low zinc concentration in breast milk. Objective: This study aimed to provide further insights into TNZD pathophysiology. Methods: SLC30A2 sequencing was performed in three unrelated Japanese mothers, whose infants developed TNZD due to low-zinc milk consumption. The effects of the identified mutations were examined using cell-based assays and luciferase reporter analysis. Results: Novel SLC30A2 mutations were identified in each mother. One harbored a heterozygous missense mutation in the ZNT2 zinc-binding site, which resulted in defective zinc transport. The other two mothers exhibited multiple heterozygous mutations in the SLC30A2 promoter, the first mutations in the SLC30A2 regulatory region reported to date. Interpretation: This report provides new genetic insights into TNZD pathogenesis in breastfed infants.

A case of ATR-X syndrome with mitochondrial respiratory chain dysfunction.

Alpha-thalassemia X-linked intellectual disability (ATR-X) syndrome is caused by a mutation in ATRX, which is essential for proper chromatin remodeling. ATRX dysfunction leads to dysregulation of many genes due to abnormal chromatin remodeling, and causes a multisystem disorder in patients with ATR-X. Because mitochondrial disorders also show multisystem involvement, whether mitochondrial function is affected in patients with ATR-X is of interest. Here, we report a case of a 4-year-old male with a mutation (NM_000489.4: c.736C > T p.Arg246Cys) in ATRX, who showed mitochondrial dysfunction with complex I deficiency. The results from our study suggest that target genes of the ATRX protein may include those responsible for mitochondrial function, and mitochondrial dysfunction may contribute to some ATR-X phenotypes.

Clinical and molecular genetic characterization of two female patients harboring the Xq27.3q28 deletion with different ratios of X chromosome inactivation.

A heterozygous deletion at Xq27.3q28 including FMR1, AFF2, and IDS causing intellectual disability and characteristic facial features is very rare in females, with only 10 patients having been reported. Here, we examined two female patients with different clinical features harboring the Xq27.3q28 deletion and determined the chromosomal breakpoints. Moreover, we assessed the X chromosome inactivation (XCI) in peripheral blood from both patients. Both patients had an almost overlapping deletion at Xq27.3q28, however, the more severe patient (Patient 1) showed skewed XCI of the normal X chromosome (79:21) whereas the milder patient (Patient 2) showed random XCI. Therefore, deletion at Xq27.3q28 critically affected brain development, and the ratio of XCI of the normal X chromosome greatly affected the clinical characteristics of patients with deletion at Xq27.3q28. As the chromosomal breakpoints were determined, we analyzed a change in chromatin domains termed topologically associated domains (TADs) using published Hi-C data on the Xq27.3q28 region, and found that only patient 1 had a possibility of a drastic change in TADs. The altered chromatin topologies on the Xq27.3q28 region might affect the clinical features of patient 1 by changing the expression of genes just outside the deletion and/or the XCI establishment during embryogenesis resulting in skewed XCI.

De novo variants in CAMK2A and CAMK2B cause neurodevelopmental disorders.

Objective: α (CAMK2A) and ß (CAMK2B) isoforms of Calcium/calmodulin-dependent protein kinase II (CaMKII) play a pivotal role in neuronal plasticity and in learning and memory processes in the brain. Here, we explore the possible involvement of α- and ß-CaMKII variants in neurodevelopmental disorders. Methods: Whole-exome sequencing was performed for 976 individuals with intellectual disability, developmental delay, and epilepsy. The effect of CAMK2A and CAMK2B variants on CaMKII structure and firing of neurons was evaluated by computational structural analysis, immunoblotting, and electrophysiological analysis. Results: We identified a total of five de novo CAMK2A and CAMK2B variants in three and two individuals, respectively. Seizures were common to three individuals with CAMK2A variants. Using a minigene splicing assay, we demonstrated that a splice site variant caused skipping of exon 11 leading to an in-frame deletion of the regulatory segment of CaMKII α. By structural analysis, four missense variants are predicted to impair the interaction between the kinase domain and the regulatory segment responsible for the autoinhibition of its kinase activity. The Thr286/Thr287 phosphorylation as a result of release from autoinhibition was increased in three mutants when the mutants were stably expressed in Neuro-2a neuroblastoma cells. Expression of a CaMKII α mutant in primary hippocampal neurons significantly increased A-type K+ currents, which facilitated spike repolarization of single action potentials. Interpretation: Our data highlight the importance of CaMKII α and CaMKII ß and their autoinhibitory regulation in human brain function, and suggest the enhancement of A-type K+ currents as a possible pathophysiological basis.

A case report of mitochondrial respiratory chain disorder in the neonatal period for which home mechanical ventilation was introduced.

We report the case of a patient born with extreme muscle hypotonia, respiratory failure, and slightly elevated serum levels of lactic acid. Histochemical examination and mitochondrial respiratory chain enzyme activities of a muscle biopsy specimen revealed reduced activities of complexes Ⅰ, Ⅲ, and Ⅳ, diagnostic of mitochondrial respiratory chain disorder. Hypertrophic cardiomyopathy developed as a complication and additional therapy was administered at 3 months after birth. He was able to be discharged to home on applied home mechanical ventilation with tracheotomy at 1 year old. The patient survived until 4 years and 10 months of age, upon which he died of bronchitis. Early-onset mitochondrial respiratory chain disorder shows very poor prognosis and long-term survival has not been reported. Prompt assessment of mitochondrial respiratory chain enzyme activities is necessary for the diagnosis of congenital nonspecific multiple-organ failure, and early intervention may achieve better prognosis for mitochondrial respiratory chain disorder.

Clinical, biochemical and metabolic characterisation of a mild form of human short-chain enoyl-CoA hydratase deficiency: significance of increased N-acetyl-S-(2-carboxypropyl)cysteine excretion.

BACKGROUND: Short-chain enoyl-CoA hydratase-ECHS1-catalyses many metabolic pathways, including mitochondrial short-chain fatty acid ß-oxidation and branched-chain amino acid catabolic pathways; however, the metabolic products essential for the diagnosis of ECHS1 deficiency have not yet been determined. The objective of this report is to characterise ECHS1 and a mild form of its deficiency biochemically, and to determine the candidate metabolic product that can be efficiently used for neonatal diagnosis. METHODS: We conducted a detailed clinical, molecular genetics, biochemical and metabolic analysis of sibling patients with ECHS1 deficiency. Moreover, we purified human ECHS1, and determined the substrate specificity of ECHS1 for five substrates via different metabolic pathways. RESULTS: Human ECHS1 catalyses the hydration of five substrates via different metabolic pathways, with the highest specificity for crotonyl-CoA and the lowest specificity for tiglyl-CoA. The patients had relatively high (∼7%) residual ECHS1 enzyme activity for crotonyl-CoA and methacrylyl-CoA caused by the compound heterozygous mutations (c.176A>G, (p.N59S) and c.413C>T, (p.A138V)) with normal mitochondrial complex I-IV activities. Affected patients excrete large amounts of N-acetyl-S-(2-carboxypropyl)cysteine, a metabolite of methacrylyl-CoA. CONCLUSIONS: Laboratory data and clinical features demonstrated that the patients have a mild form of ECHS1 deficiency harbouring defective valine catabolic and ß-oxidation pathways. N-Acetyl-S-(2-carboxypropyl) cysteine level was markedly high in the urine of the patients, and therefore, N-acetyl-S-(2-carboxypropyl)cysteine was regarded as a candidate metabolite for the diagnosis of ECHS1 deficiency. This metabolite is not part of current routine metabolic screening protocols, and its inclusion, therefore, holds immense potential in accurate diagnosis.

Three patients manifesting early infantile epileptic spasms associated with 2q24.3 microduplications.

BACKGROUND: Recent development of genetic analyses enabled us to reveal underlying genetic causes of the patients with epileptic encephalopathy in infancy. Mutations of voltage-gated sodium channel type I alpha subunit gene (SCN1A) are to be causally related with several phenotypes of epilepsy, generalized epilepsy with febrile seizure plus (GEFS+), Dravet syndrome, and other infantile epileptic encephalopathies. In addition to SCN1A, contiguous genes such as SCN2A and SCN3A in 2q24.3 are also reported to have contribution to epileptic seizures. Therefore, gene abnormality involving this region is reasonable to contribute to epilepsy manifestation. RESULTS: We encountered three patients with 2q24.3 microduplication diagnosed by Array comparative genomic hybridization array (aCGH). They developed partial seizures and epileptic spasms in their early infantile periods and showed remarkable developmental delay, although their seizures disappeared from 11 to 14 months of age. One of three patients had 2q24.3 microduplication which excludes SCN1A. Therefore, characteristics of epilepsy with 2q24.3 microduplication do not necessarily need duplication of SCN1A. This study suggested that 2q24.3 microduplication is one of the causes for early infantile epileptic spasms. Epileptic spasms associated with 2q24.3 microduplications may have better seizure outcome comparing with other etiologies.

Spinocerebellar ataxias type 27 derived from a disruption of the fibroblast growth factor 14 gene with mimicking phenotype of paroxysmal non-kinesigenic dyskinesia.

Many types of spinocerebellar ataxias (SCAs) manifest as progressive disorders with cerebellar involvement. SCA type 27 (SCA27) is a rare type of SCA caused by mutations in the fibroblast growth factor 14 gene (FGF14). FGF14 disruption caused by a de novo reciprocal chromosomal translocation between chromosomes 13 and 21 was identified in a patient with the phenotype of paroxysmal non-kinesigenic dyskinesia (PNKD). This indicated genetic heterogeneity of PNKD, since 60% of the patients with PNKD exhibit mutations in another gene responsible for PNKD, the myofibrillogenesis regulator 1 gene (MR-1). We hypothesized that the remaining 40% of patients with PNKD may have FGF14 mutations; therefore, the nucleotide sequences of MR-1 and FGF14 were analyzed in another six patients with PNKD, but no nucleotide alterations were observed in these genes for these patients. Further studies should be conducted on the phenotypic heterogeneity of FGF14 mutations and/or haploinsufficiency in SCA27 and PNKD.

Cytokine profiles before and after exchange transfusion in a neonate with transient myeloproliferative disorder and hepatic fibrosis.

SUMMARY: To study the effect of exchange transfusion on cytokine profiles in a patient with transient myeloproliferative disorder and hepatic fibrosis in which cytokines were measured before and after exchange transfusion. A newborn female was diagnosed with Down syndrome phenotypically and on karyotyping. Laboratory data showed a high leukocyte count with blast cells in the peripheral blood and liver dysfunction. Exchange transfusion was performed on day 1. However, respiratory distress and multiorgan failure progressed, and she died after 16 days. Of the cytokines examined, transforming growth factor-beta1 and interleukin-7 were extremely high before exchange transfusion, and decreased after exchange transfusion.