Biallelic variants in SLC4A10 encoding a sodium-dependent bicarbonate transporter lead to a neurodevelopmental disorder.

PURPOSE: SLC4A10 encodes a plasma membrane-bound transporter, which mediates Na+-dependent HCO3- import, thus mediating net acid extrusion. Slc4a10 knockout mice show collapsed brain ventricles, an increased seizure threshold, mild behavioral abnormalities, impaired vision, and deafness. METHODS: Utilizing exome/genome sequencing in families with undiagnosed neurodevelopmental disorders and international data sharing, 11 patients from 6 independent families with biallelic variants in SLC4A10 were identified. Clinico-radiological and dysmorphology assessments were conducted. A minigene assay, localization studies, intracellular pH recordings, and protein modeling were performed to study the possible functional consequences of the variant alleles. RESULTS: The families harbor 8 segregating ultra-rare biallelic SLC4A10 variants (7 missense and 1 splicing). Phenotypically, patients present with global developmental delay/intellectual disability and central hypotonia, accompanied by variable speech delay, microcephaly, cerebellar ataxia, facial dysmorphism, and infrequently, epilepsy. Neuroimaging features range from some non-specific to distinct neuroradiological findings, including slit ventricles and a peculiar form of bilateral curvilinear nodular heterotopia. In silico analyses showed 6 of 7 missense variants affect evolutionarily conserved residues. Functional analyses supported the pathogenicity of 4 of 7 missense variants. CONCLUSION: We provide evidence that pathogenic biallelic SLC4A10 variants can lead to neurodevelopmental disorders characterized by variable abnormalities of the central nervous system, including altered brain ventricles, thus resembling several features observed in knockout mice.

Recurrent De Novo NAHR Reciprocal Duplications in the ATAD3 Gene Cluster Cause a Neurogenetic Trait with Perturbed Cholesterol and Mitochondrial Metabolism.

Recent studies have identified both recessive and dominant forms of mitochondrial disease that result from ATAD3A variants. The recessive form includes subjects with biallelic deletions mediated by non-allelic homologous recombination. We report five unrelated neonates with a lethal metabolic disorder characterized by cardiomyopathy, corneal opacities, encephalopathy, hypotonia, and seizures in whom a monoallelic reciprocal duplication at the ATAD3 locus was identified. Analysis of the breakpoint junction fragment indicated that these 67 kb heterozygous duplications were likely mediated by non-allelic homologous recombination at regions of high sequence identity in ATAD3A exon 11 and ATAD3C exon 7. At the recombinant junction, the duplication allele produces a fusion gene derived from ATAD3A and ATAD3C, the protein product of which lacks key functional residues. Analysis of fibroblasts derived from two affected individuals shows that the fusion gene product is expressed and stable. These cells display perturbed cholesterol and mitochondrial DNA organization similar to that observed for individuals with severe ATAD3A deficiency. We hypothesize that the fusion protein acts through a dominant-negative mechanism to cause this fatal mitochondrial disorder. Our data delineate a molecular diagnosis for this disorder, extend the clinical spectrum associated with structural variation at the ATAD3 locus, and identify a third mutational mechanism for ATAD3 gene cluster variants. These results further affirm structural variant mutagenesis mechanisms in sporadic disease traits, emphasize the importance of copy number analysis in molecular genomic diagnosis, and highlight some of the challenges of detecting and interpreting clinically relevant rare gene rearrangements from next-generation sequencing data.

Functional insight into a neurodevelopmental disorder caused by missense variants in an RNA-binding protein, RBM10.

The RNA-binding motif protein 10, RBM10, is an RNA splicing regulator essential for development. Loss-of-function RBM10 variants are associated with TARP syndrome, a severe X-linked recessive condition in males. We report a 3-year-old male with a mild phenotype, consisting of cleft palate, hypotonia, developmental delay, and minor dysmorphisms, associated with a missense RBM10 variant, c.943T>C, p.Ser315Pro, affecting the RRM2 RNA-binding domain. His clinical features were similar to a previously reported case associated with a missense variant. The p.Ser315Pro mutant protein was expressed normally in the nucleus, but its expression level and protein stability were slightly reduced. Nuclear magnetic resonance spectroscopy showed that the structure and the RNA-binding ability of the RRM2 domain with the p.Ser315Pro were unaffected. However, it affects the alternative splicing regulations of downstream genes, NUMB and TNRC6A, and its splicing alteration patterns were variable depending on target transcripts. In summary, a novel germline missense RBM10 p.Ser315Pro variant that causes functional changes in the expression of its downstream genes results in a non-lethal phenotype associated with developmental delays. The functional alteration effects depend on the residues affected by missense variants. Our findings are expected to bring broader insights into the RBM10-associated genotype-phenotype relationships by delineating the molecular mechanism of RBM10 functions.

Delineating the genotypic and phenotypic spectrum of HECW2-related neurodevelopmental disorders.

BACKGROUND: Variants in HECW2 have recently been reported to cause a neurodevelopmental disorder with hypotonia, seizures and impaired language; however, only six variants have been reported and the clinical characteristics have only broadly been defined. METHODS: Molecular and clinical data were collected from clinical and research cohorts. Massive parallel sequencing was performed and identified individuals with a HECW2-related neurodevelopmental disorder. RESULTS: We identified 13 novel missense variants in HECW2 in 22 unpublished cases, of which 18 were confirmed to have a de novo variant. In addition, we reviewed the genotypes and phenotypes of previously reported and new cases with HECW2 variants (n=35 cases). All variants identified are missense, and the majority of likely pathogenic and pathogenic variants are located in or near the C-terminal HECT domain (88.2%). We identified several clustered variants and four recurrent variants (p.(Arg1191Gln);p.(Asn1199Lys);p.(Phe1327Ser);p.(Arg1330Trp)). Two variants, (p.(Arg1191Gln);p.(Arg1330Trp)), accounted for 22.9% and 20% of cases, respectively. Clinical characterisation suggests complete penetrance for hypotonia with or without spasticity (100%), developmental delay/intellectual disability (100%) and developmental language disorder (100%). Other common features are behavioural problems (88.9%), vision problems (83.9%), motor coordination/movement (75%) and gastrointestinal issues (70%). Seizures were present in 61.3% of individuals. Genotype-phenotype analysis shows that HECT domain variants are more frequently associated with cortical visual impairment and gastrointestinal issues. Seizures were only observed in individuals with variants in or near the HECT domain. CONCLUSION: We provide a comprehensive review and expansion of the genotypic and phenotypic spectrum of HECW2 disorders, aiding future molecular and clinical diagnosis and management.

Consolidation of the clinical and genetic definition of a SOX4-related neurodevelopmental syndrome.

BACKGROUND: A neurodevelopmental syndrome was recently reported in four patients with SOX4 heterozygous missense variants in the high-mobility-group (HMG) DNA-binding domain. The present study aimed to consolidate clinical and genetic knowledge of this syndrome. METHODS: We newly identified 17 patients with SOX4 variants, predicted variant pathogenicity using in silico tests and in vitro functional assays and analysed the patients' phenotypes. RESULTS: All variants were novel, distinct and heterozygous. Seven HMG-domain missense and five stop-gain variants were classified as pathogenic or likely pathogenic variant (L/PV) as they precluded SOX4 transcriptional activity in vitro. Five HMG-domain and non-HMG-domain missense variants were classified as of uncertain significance (VUS) due to negative results from functional tests. When known, inheritance was de novo or from a mosaic unaffected or non-mosaic affected parent for patients with L/PV, and from a non-mosaic asymptomatic or affected parent for patients with VUS. All patients had neurodevelopmental, neurological and dysmorphic features, and at least one cardiovascular, ophthalmological, musculoskeletal or other somatic anomaly. Patients with L/PV were overall more affected than patients with VUS. They resembled patients with other neurodevelopmental diseases, including the SOX11-related and Coffin-Siris (CSS) syndromes, but lacked the most specific features of CSS. CONCLUSION: These findings consolidate evidence of a fairly non-specific neurodevelopmental syndrome due to SOX4 haploinsufficiency in neurogenesis and multiple other developmental processes.

A Novel Kleefstra Syndrome-associated Variant That Affects the Conserved TPLX Motif within the Ankyrin Repeat of EHMT1 Leads to Abnormal Protein Folding.

Kleefstra syndrome (KS) (Mendelian Inheritance in Man (MIM) no. 610253), also known as 9q34 deletion syndrome, is an autosomal dominant disorder caused by haploinsufficiency of euchromatic histone methyltransferase-1 (EHMT1). The clinical phenotype of KS includes moderate to severe intellectual disability with absent speech, hypotonia, brachycephaly, congenital heart defects, and dysmorphic facial features with hypertelorism, synophrys, macroglossia, protruding tongue, and prognathism. Only a few cases of de novo missense mutations in EHMT1 giving rise to KS have been described. However, some EHMT1 variants have been described in individuals presenting with autism spectrum disorder or mild intellectual disability, suggesting that the phenotypic spectrum resulting from EHMT1 alterations may be quite broad. In this report, we describe two unrelated patients with complex medical histories consistent with KS in whom next generation sequencing identified the same novel c.2426C>T (p.P809L) missense variant in EHMT1 To examine the functional significance of this novel variant, we performed molecular dynamics simulations of the wild type and p.P809L variant, which predicted that the latter would have a propensity to misfold, leading to abnormal histone mark binding. Recombinant EHMT1 p.P809L was also studied using far UV circular dichroism spectroscopy and intrinsic protein fluorescence. These functional studies confirmed the model-based hypotheses and provided evidence for protein misfolding and aberrant target recognition as the underlying pathogenic mechanism for this novel KS-associated variant. This is the first report to suggest that missense variants in EHMT1 that lead to protein misfolding and disrupted histone mark binding can lead to KS.

Psychiatric disease in an adolescent as a harbinger of cerebral X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (XALD) typically presents as a childhood cerebral demyelinating form, as an adult-onset adrenomyeloneuropathy or as adrenocortical insufficiency. Cerebral demyelination presenting in adolescence is unusual. We present an 17-year-old boy with adolescent-onset XALD initially manifesting with slowly progressive psychiatric symptoms. He was initially diagnosed with attention-deficit hyperactivity disorder and an acute psychosis. However, he was ultimately diagnosed with XALD based on his clinical course, neuroimaging findings and biochemical abnormalities. This case reiterates the atypical presentations of adolescent-onset cerebral XALD that may go unrecognised and misdiagnosed as a neurodevelopmental or psychiatric disease. Treatments for cerebral ALD are potentially life-saving, particularly when given early in the disease course.

High Incidence of Noonan Syndrome Features Including Short Stature and Pulmonic Stenosis in Patients carrying NF1 Missense Mutations Affecting p.Arg1809: Genotype-Phenotype Correlation.

Neurofibromatosis type 1 (NF1) is one of the most frequent genetic disorders, affecting 1:3,000 worldwide. Identification of genotype-phenotype correlations is challenging because of the wide range clinical variability, the progressive nature of the disorder, and extreme diversity of the mutational spectrum. We report 136 individuals with a distinct phenotype carrying one of five different NF1 missense mutations affecting p.Arg1809. Patients presented with multiple café-au-lait macules (CALM) with or without freckling and Lisch nodules, but no externally visible plexiform neurofibromas or clear cutaneous neurofibromas were found. About 25% of the individuals had Noonan-like features. Pulmonic stenosis and short stature were significantly more prevalent compared with classic cohorts (P < 0.0001). Developmental delays and/or learning disabilities were reported in over 50% of patients. Melanocytes cultured from a CALM in a segmental NF1-patient showed two different somatic NF1 mutations, p.Arg1809Cys and a multi-exon deletion, providing genetic evidence that p.Arg1809Cys is a loss-of-function mutation in the melanocytes and causes a pigmentary phenotype. Constitutional missense mutations at p.Arg1809 affect 1.23% of unrelated NF1 probands in the UAB cohort, therefore this specific NF1 genotype-phenotype correlation will affect counseling and management of a significant number of patients.

Infantile hypertrophic cardiomyopathy associated with a novel MYL3 mutation.

Mutations in genes encoding cardiac sarcomeric proteins are thought to be a very rare cause of hypertrophic cardiomyopathy (HCM) in infants and young children. We report on genetic and histopathological findings in a 3-month-old infant presenting with severe progressive HCM arising from a mutation in the gene encoding the essential light chain of myosin (MYL3). The patient was found to have a novel, paternally inherited pathogenic c.530 A>G mutation in exon 5 of the MYL3 gene. His father was asymptomatic. Although, MYL3 mutations have been previously associated with adult-onset HCM, it has not been seen in infantile forms. As such, this case adds to the emerging evidence demonstrating that familial disease associated with mutations in cardiac sarcomere protein genes may have an important role in infants and children with HCM. In addition, this case highlights the marked phenotypic heterogeneity associated with sarcomeric protein mutations both within and between families.

A complex 6p25 rearrangement in a child with multiple epiphyseal dysplasia.

Genomic rearrangements are increasingly recognized as important contributors to human disease. Here we report on an 11½-year-old child with myopia, Duane retraction syndrome, bilateral mixed hearing loss, skeletal anomalies including multiple epiphyseal dysplasia, and global developmental delay, and a complex 6p25 genomic rearrangement. We have employed oligonucleotide-based comparative genomic hybridization arrays (aCGH) of different resolutions (44 and 244K) as well as a 1 M single nucleotide polymorphism (SNP) array to analyze this complex rearrangement. Our analyses reveal a complex rearrangement involving a ∼2.21 Mb interstitial deletion, a ∼240 kb terminal deletion, and a 70-80 kb region in between these two deletions that shows maintenance of genomic copy number. The interstitial deletion contains eight known genes, including three Forkhead box containing (FOX) transcription factors (FOXQ1, FOXF2, and FOXC1). The region maintaining genomic copy number partly overlaps the dual specificity protein phosphatase 22 (DUSP22) gene. Array analyses suggest a homozygous loss of genomic material at the 5' end of DUSP22, which was corroborated using TaqMan® copy number analysis. It is possible that this homozygous genomic loss may render both copies of DUSP22 or its products non-functional. Our analysis suggests a rearrangement mechanism distinct from a previously reported replication-based error-prone mechanism without template switching for a specific 6p25 rearrangement with a 1.22 Mb interstitial deletion. Our study demonstrates the utility and limitations of using oligonucleotide-based aCGH and SNP array technologies of increasing resolutions in order to identify complex DNA rearrangements and gene disruptions.

A 3'-truncating FTL mutation associated with hypoferritinemia without neuroferritinopathy.

Mutations in the gene for the ferritin light chain (FTL) often present with hypoferritinemia associated with progressive, late onset extrapyramidal dysfunction. However, it has been suggested that some FTL mutations may impact ferritin levels without any neurological manifestations. We report on a FTL mutation in a three generation family with autosomal dominant hypoferritinemia without neurodegeneration. The 4 year old proband was identified with longstanding history of hypoferritinemia without evidence of anemia. Brain MRI did not show any evidence of iron deposition. It was found that the patient's 19 month old sister, 30 year old mother and 58 year old maternal grandmother also had hypoferritinemia and normal iron levels. Over the next nine years, none of these persons had any evidence of neurological dysfunction, including movement disorders, gait disturbances, behavioral or psychiatric dysfunction. Whole exome sequencing revealed a heterozygous interstitial deletion of at least 5 kb within cytogenic band 19q13.33 involving exons 3 and 4 of FTL in all affected family members. This 3' FTL deletion is predicted to create a significantly truncated protein product. We conclude that haploinsufficiency of FTL may be associated with hypoferritinemia without neurological dysfunction.

A Case of 45,X/46,XY Mosaicism Presenting as Swyer Syndrome.

BACKGROUND: Swyer syndrome is a difference of sex development that is typically associated with mutations in genes responsible for testicular development. It is speculated that some cases may result from cryptic 45,X/46,XY mosaicism leading to abnormal gonadal development. The presence or absence of a 45,X lineage is important for prognosis and management. CASE: We present a case of apparent Swyer syndrome associated with a 46,XY chromosomal complement in lymphocytes and 45,X/46,XY mosaicism on analysis of her noncancerous gonad. Gonadal histology was consistent with a 45,X phenotype. SUMMARY AND CONCLUSION: This case demonstrates the clinical variability in the presentation of 45,X/46,XY mosaicism and highlights the importance of thorough genetic testing that includes consideration of chromosomal mosaicism. We will discuss the implications of this diagnosis for management.

Contribution of the closing base pair to exceptional stability in RNA tetraloops: roles for molecular mimicry and electrostatic factors.

Hairpins are common RNA secondary structures that play multiple roles in nature. Tetraloops are the most frequent RNA hairpin loops and are often phylogenetically conserved. For both the UNCG and GNRA families, CG closing base pairs (cbps) confer exceptional thermodynamic stability but the molecular basis for this has remained unclear. We propose that, despite having very different overall folds, these two tetraloop families achieve stability by presenting the same functionalities to the major groove edge of the CG cbp. Thermodynamic contributions of this molecular mimicry were investigated using substitutions at the nucleobase and functional group levels. By either interrupting or deleting loop-cbp electrostatic interactions, which were identified by solving the nonlinear Poisson-Boltzmann (NLPB) equation, stability changed in a manner consistent with molecular mimicry. We also observed a linear relationship between DeltaG(o)(37) and log[Na(+)] for both families, and loops with a CG cbp had a decreased dependence of stability on salt. NLPB calculations revealed that, for both UUCG and GAAA tetraloops, the GC cbp form has a higher surface charge density, although it arises from changes in loop compaction for UUCG and changes in loop configuration for GAAA. Higher surface charge density leads to stronger interactions of GC cbp loops with solvent and salt, which explains the correlation between experimental and calculated trends of free energy with salt. Molecular mimicry as evidenced in these two stable but otherwise unrelated tetraloops may underlie common functional roles in other RNA and DNA motifs.

Ethnic heterogeneity in the longitudinal effects of placental vascular blood flow on birthweight.

OBJECTIVE: Our goals were: (1) to estimate the longitudinal trends in uterine artery (UtArt) and umbilical artery (UmArt) resistance indices (RIs) in different ethnic strata; (2) to estimate time-dependent changes across gestation in the influence of variation in UtArt and UmArt RI on variation in birthweight in different ethnic strata; and (3) to determine the optimum set of UtArt and UmArt RIs for predicting birthweight in different ethnic strata. STUDY DESIGN: Analyses were carried out on data collected in a prospective study of 535 multiethnic gravidas recruited from the Cedars-Sinai Medical Center (Los Angeles, CA). Baseline maternal characteristics were recorded at time of entry into the study. UtArt and UmArt RIs were measured on 3 occasions during pregnancy (visit 1, 16-20 weeks' gestation; visit 2, 21-29 weeks' gestation; and visit 3, 30-36 weeks' gestation). The outcome for this study was gestational age-adjusted birthweight (aBW). RESULTS: The average UtArt and UmArt RI decreased steadily across gestation for all ethnicities. The average UtArt RI at each visit and the average rate of change between visits were not significantly different among the ethnicities. However, the UmArt RI measured at visit 3 and its rate of change in the last trimester were significantly different among the ethnic groups (P < .02). After adjustment for traditional risk factors for fetal growth restriction, the magnitude and rate of change of UtArt RI significantly predicted aBW only in Hispanic women, whereas the magnitude and rate of change of UmArt RI predicted aBW only in African American women. The most parsimonious combination of UtArt and UmArt RI measurements at visits 1, 2, and 3 that predicted statistically significant variation in aBW differed by ethnicity. CONCLUSION: The relationships between aBW and longitudinally collected measures of UtArt and UmArt RI depend on the context defined by ethnicity and time of measurement after adjusting for a parsimoniously selected subset of traditional risk factors.

A Case of Congenital Hypopituitarism Associated With a 1p31 Microdeletion: A Possible Role for LEPR and JAK1.

CONTEXT: Genetic defects affecting the expression and function of factors involved in pituitary development have been found to be associated with congenital hypopituitarism (CH). However, for most cases of CH, the etiology remains unknown. CASE DESCRIPTION: We present an unusual case of an infant with CH, associated with septo-optic dysplasia with an absent anterior pituitary and an ectopic posterior pituitary gland, resulting from a de novo 8.04-Mb interstitial deletion of chromosome 1p31.1-1p31.3. The deleted region includes several genes that might be involved in pituitary development, including LEPR and JAK1. CONCLUSIONS: Haploinsufficiency of LEPR and/or JAK1 might be associated with CH. This finding suggests a role for LEPR-mediated glycoprotein 130 signaling in human pituitary development.

Preterm Delivery as a Unique Pathophysiologic State Characterized by Maternal Soluble FMS-Like Tyrosine Kinase 1 and Uterine Artery Resistance During Pregnancy: A Longitudinal Cohort Study.

BACKGROUND: Preterm delivery (PTD) may be characterized by altered interrelationships among angiogenic factors and measures of placental function. We analyzed the longitudinal relationship between maternal serum concentrations of soluble fms-like tyrosine kinase 1 (sFlt1), an important antiangiogenic factor, and uterine artery resistance in pregnancies resulting in preterm and term deliveries. METHODS: Data were collected in a longitudinal cohort study involving 278 women monitored at 6 to 10, 10 to 14, 16 to 20, 22 to 26, and 32 to 36 weeks of gestation. Concentrations of maternal serum sFlt1 were determined using solid-phase enzyme-linked immunosorbent assay, and uterine artery resistance indices (RI) were measured by Doppler velocimetry at each interval. Preterm delivery was defined as birth before 37-weeks completed gestation. Data analyses used multivariable repeated measures regression models. RESULTS: Uterine artery RI decreased across gestation. As pregnancy progressed, RI trajectories diverged for term and preterm deliveries; the mean RI was significantly higher in third trimester for pregnancies resulting in PTD ( P = .08). sFlt1 was stable through 21 3/7 weeks of gestation and then increased rapidly; women who delivered preterm had significantly higher sFlt1 levels in the third trimester ( P = .04). The relationship between uterine artery RI and sFlt1 from the prior visit was significantly different between the groups ( P < .0001). For term deliveries, higher sFlt1 concentrations were associated with a smaller RI at the subsequent visit (ß = -.08, 95% confidence interval [CI]: -0.14 to -0.02). For PTD, higher sFlt1 concentrations were associated with a larger uterine artery RI (ß = .14, 95% CI: 0.06 to 0.22). CONCLUSION: PTD is characterized by altered relationships between angiogenic factors and placental vascular blood flow starting in early pregnancy.