WiTNNess: An international natural history study of infantile-onset TNNT1 myopathy

OBJECTIVE

We created WiTNNess as a hybrid prospective/cross-sectional observational study to simulate a clinical trial for infantile-onset TNNT1 myopathy. Our aims were to identify populations for future trial enrollment, rehearse outcome assessments, specify endpoints, and refine trial logistics.

METHODS

Eligible participants had biallelic pathogenic variants of TNNT1 and infantile-onset proximal weakness without confounding conditions. The primary endpoint was ventilator-free survival. "Thriving" was a secondary endpoint defined as the ability to swallow and grow normally without non-oral feeding support. Endpoints of gross motor function included independent sitting and standing as defined by the Word Health Organization, a novel TNNT1 abbreviated motor score, and video mapping of limb movement. We recorded adverse events, concomitant medications, and indices of organ function to serve as comparators of safety in future trials.

RESULTS

Sixteen children were enrolled in the aggregate cohort (6 prospective, 10 cross-sectional; median census age 2.3 years, range 0.5-13.8). Median ventilator-free survival was 20.2 months and probability of death or permanent mechanical ventilation was 100% by age 60 months. All six children (100%) in the prospective arm failed to thrive by age 12 months. Only 2 of 16 (13%) children in the aggregate cohort sat independently and none stood alone. Novel exploratory motor assessments also proved informative. Laboratory and imaging data suggest that primary manifestations of TNNT1 deficiency are restricted to skeletal muscle.

INTERPRETATION

WiTNNess allowed us to streamline and economize the collection of historical control data without compromising scientific rigor, and thereby establish a sound operational framework for future clinical trials.

Pathogenic variants in SLF2 and SMC5 cause segmented chromosomes and mosaic variegated hyperploidy

Embryonic development is dictated by tight regulation of DNA replication, cell division and differentiation. Mutations in DNA repair and replication genes disrupt this equilibrium, giving rise to neurodevelopmental disease characterized by microcephaly, short stature and chromosomal breakage. Here, we identify biallelic variants in two components of the RAD18-SLF1/2-SMC5/6 genome stability pathway, SLF2 and SMC5, in 11 patients with microcephaly, short stature, cardiac abnormalities and anemia. Patient-derived cells exhibit a unique chromosomal instability phenotype consisting of segmented and dicentric chromosomes with mosaic variegated hyperploidy. To signify the importance of these segmented chromosomes, we have named this disorder Atelís (meaning - incomplete) Syndrome. Analysis of Atelís Syndrome cells reveals elevated levels of replication stress, partly due to a reduced ability to replicate through G-quadruplex DNA structures, and also loss of sister chromatid cohesion. Together, these data strengthen the functional link between SLF2 and the SMC5/6 complex, highlighting a distinct role for this pathway in maintaining genome stability.

Clinical characterization of familial hypercholesterolemia due to an amish founder mutation in Apolipoprotein B

Background

Familial hypercholesterolemia (FH) due to a founder variant in Apolipoprotein B (ApoB^R3500Q) is reported in 12% of the Pennsylvania Amish community. By studying a cohort of ApoB^R3500Q heterozygotes and homozygotes, we aimed to characterize the biochemical and cardiac imaging features in children and young adults with a common genetic background and similar lifestyle.

Methods

We employed advanced lipid profile testing, carotid intima media thickness (CIMT), pulse wave velocity (PWV), and peripheral artery tonometry (PAT) to assess atherosclerosis in a cohort of Amish ApoB^R3500Q heterozygotes (n = 13), homozygotes (n = 3), and their unaffected, age-matched siblings (n = 9). ApoB^R3500Q homozygotes were not included in statistical comparisons.

Results

LDL cholesterol (LDL-C) was significantly elevated among ApoB^R3500Q heterozygotes compared to sibling controls, though several ApoB^R3500Q heterozygotes had LDL-C levels in the normal range. LDL particles (LDL-P), small, dense LDL particles, and ApoB were also significantly elevated among subjects with ApoB^R3500Q. Despite these differences in serum lipids and particles, CIMT and PWV were not significantly different between ApoB^R3500Q heterozygotes and controls in age-adjusted analysis.

Conclusions

We provide a detailed description of the serum lipids, atherosclerotic plaque burden, vascular stiffness, and endothelial function among children and young adults with FH due to heterozygous ApoB^R3500Q. Fasting LDL-C was lower than what is seen with other forms of FH, and even normal in several ApoB^R3500Q heterozygotes, emphasizing the importance of cascade genetic testing among related individuals for diagnosis. We found increased number of LDL particles among ApoB^R3500Q heterozygotes but an absence of detectable atherosclerosis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-022-02539-3.

APC7 mediates ubiquitin signaling in constitutive heterochromatin in the developing mammalian brain

Neurodevelopmental cognitive disorders provide insights into mechanisms of human brain development. Here, we report an intellectual disability syndrome caused by the loss of APC7, a core component of the E3 ubiquitin ligase anaphase promoting complex (APC). In mechanistic studies, we uncover a critical role for APC7 during the recruitment and ubiquitination of APC substrates. In proteomics analyses of the brain from mice harboring the patient-specific APC7 mutation, we identify the chromatin-associated protein Ki-67 as an APC7-dependent substrate of the APC in neurons. Conditional knockout of the APC coactivator protein Cdh1, but not Cdc20, leads to the accumulation of Ki-67 protein in neurons in vivo, suggesting that APC7 is required for the function of Cdh1-APC in the brain. Deregulated neuronal Ki-67 upon APC7 loss localizes predominantly to constitutive heterochromatin. Our findings define an essential function for APC7 and Cdh1-APC in neuronal heterochromatin regulation, with implications for understanding human brain development and disease.

Nusinersen by subcutaneous intrathecal catheter for symptomatic spinal muscular atrophy patients with complex spine anatomy

INTRODUCTION/AIMS

Intrathecal administration of nusinersen is challenging in patients with spinal muscular atrophy (SMA) who have spine deformities or fusions. We prospectively studied the safety and efficacy of nusinersen administration via an indwelling subcutaneous intrathecal catheter (SIC) for SMA patients with advanced disease.

METHODS

Seventeen participants commenced nusinersen therapy between 2.7 and 31.5 years of age and received 9 to 12 doses via SIC. Safety was assessed in all participants. A separate efficacy analysis comprised 11 nonambulatory, treatment-naive SMA patients (18.1 ± 6.8 years) with three SMN2 copies and complex spine anatomy.

RESULTS

In the safety analysis, 14 treatment-related adverse events (AEs) occurred among 12 (71%) participants; all were related to the SIC and not nusinersen. Device-related AEs interfered with 2.5% of nusinersen doses. Four SICs (24%) required surgical revision due to mechanical malfunction with or without cerebrospinal fluid leak (n = 2), and one (6%) was removed due to Staphylococcus epidermidis meningitis. In the efficacy analysis, mean performance on the nine-hole peg test improved in dominant (15.9%, P = 0.012) and nondominant (19.0%, P = 0.008) hands and grip strength increased by 44.9% (P = 0.031). We observed no significant changes in motor scales, muscle force, pulmonary function, or SMA biomarkers. All participants in the efficacy cohort reported one or more subjective improvement(s) in endurance, purposeful hand use, arm strength, head control, and/or speech.

DISCUSSION

For SMA patients with complex spine anatomy, the SIC allows for reliable outpatient administration of nusinersen that results in meaningful improvements in upper limb function, but introduces risks of technical malfunction and iatrogenic infection.

Cortical overgrowth in a preclinical forebrain organoid model of CNTNAP2-associated autism spectrum disorder

We utilized forebrain organoids generated from induced pluripotent stem cells of patients with a syndromic form of Autism Spectrum Disorder (ASD) with a homozygous protein-truncating mutation in CNTNAP2, to study its effects on embryonic cortical development. Patients with this mutation present with clinical characteristics of brain overgrowth. Patient-derived forebrain organoids displayed an increase in volume and total cell number that is driven by increased neural progenitor proliferation. Single-cell RNA sequencing revealed PFC-excitatory neurons to be the key cell types expressing CNTNAP2. Gene ontology analysis of differentially expressed genes (DEgenes) corroborates aberrant cellular proliferation. Moreover, the DEgenes are enriched for ASD-associated genes. The cell-type-specific signature genes of the CNTNAP2-expressing neurons are associated with clinical phenotypes previously described in patients. The organoid overgrowth phenotypes were largely rescued after correction of the mutation using CRISPR-Cas9. This CNTNAP2-organoid model provides opportunity for further mechanistic inquiry and development of new therapeutic strategies for ASD.

De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy

Adaptor protein (AP) complexes mediate selective intracellular vesicular trafficking and polarized localization of somatodendritic proteins in neurons. Disease-causing alleles of various subunits of AP complexes have been implicated in several heritable human disorders, including intellectual disabilities (IDs). Here, we report two bi-allelic (c.737C>A [p.Pro246His] and c.1105A>G [p.Met369Val]) and eight de novo heterozygous variants (c.44G>A [p.Arg15Gln], c.103C>T [p.Arg35Trp], c.104G>A [p.Arg35Gln], c.229delC [p.Gln77Lys^∗11], c.399_400del [p.Glu133Aspfs^∗37], c.747G>T [p.Gln249His], c.928-2A>C [p.?], and c.2459C>G [p.Pro820Arg]) in AP1G1, encoding gamma-1 subunit of adaptor-related protein complex 1 (AP1γ1), associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities. The AP1γ1-mediated adaptor complex is essential for the formation of clathrin-coated intracellular vesicles. In silico analysis and 3D protein modeling simulation predicted alteration of AP1γ1 protein folding for missense variants, which was consistent with the observed altered AP1γ1 levels in heterologous cells. Functional studies of the recessively inherited missense variants revealed no apparent impact on the interaction of AP1γ1 with other subunits of the AP-1 complex but rather showed to affect the endosome recycling pathway. Knocking out ap1g1 in zebrafish leads to severe morphological defect and lethality, which was significantly rescued by injection of wild-type AP1G1 mRNA and not by transcripts encoding the missense variants. Furthermore, microinjection of mRNAs with de novo missense variants in wild-type zebrafish resulted in severe developmental abnormalities and increased lethality. We conclude that de novo and bi-allelic variants in AP1G1 are associated with neurodevelopmental disorder in diverse populations.

A recurring NFS1 pathogenic variant causes a mitochondrial disorder with variable intra-familial patient outcomes

Iron‑sulfur clusters (FeSCs) are vital components of a variety of essential proteins, most prominently within mitochondrial respiratory chain complexes I-III; Fe-S assembly and distribution is performed via multi-step pathways. Variants affecting several proteins in these pathways have been described in genetic disorders, including severe mitochondrial disease. Here we describe a Christian Arab kindred with two infants that died due to mitochondrial disorder involving Fe-S containing respiratory chain complexes and a third sibling who survived the initial crisis. A homozygous missense variant in NFS1: c.215G>A; p.Arg72Gln was detected by whole exome sequencing. The NFS1 gene encodes a cysteine desulfurase, which, in complex with ISD11 and ACP, initiates the first step of Fe-S formation. Arginine at position 72 plays a role in NFS1-ISD11 complex formation; therefore, its substitution with glutamine is expected to affect complex stability and function. Interestingly, this is the only pathogenic variant ever reported in the NFS1 gene, previously described once in an Old Order Mennonite family presenting a similar phenotype with intra-familial variability in patient outcomes. Analysis of datasets from both populations did not show a common haplotype, suggesting this variant is a recurrent de novo variant. Our report of the second case of NFS1-related mitochondrial disease corroborates the pathogenicity of this recurring variant and implicates it as a hot-spot variant. While the genetic resolution allows for prenatal diagnosis for the family, it also raises critical clinical questions regarding follow-up and possible treatment options of severely affected and healthy homozygous individuals with mitochondrial co-factor therapy or cysteine supplementation.

Glutaric acidemia type 1: Treatment and outcome of 168 patients over three decades

Glutaric acidemia type 1 (GA1) is a disorder of cerebral organic acid metabolism resulting from biallelic mutations of GCDH. Without treatment, GA1 causes striatal degeneration in >80% of affected children before two years of age. We analyzed clinical, biochemical, and developmental outcomes for 168 genotypically diverse GA1 patients managed at a single center over 31 years, here separated into three treatment cohorts: children in Cohort I (n = 60; DOB 2006-2019) were identified by newborn screening (NBS) and treated prospectively using a standardized protocol that included a lysine-free, arginine-enriched metabolic formula, enteral l-carnitine (100 mg/kg•day), and emergency intravenous (IV) infusions of dextrose, saline, and l-carnitine during illnesses; children in Cohort II (n = 57; DOB 1989-2018) were identified by NBS and treated with natural protein restriction (1.0-1.3 g/kg•day) and emergency IV infusions; children in Cohort III (n = 51; DOB 1973-2016) did not receive NBS or special diet. The incidence of striatal degeneration in Cohorts I, II, and III was 7%, 47%, and 90%, respectively (p < .0001). No neurologic injuries occurred after 19 months of age. Among uninjured children followed prospectively from birth (Cohort I), measures of growth, nutritional sufficiency, motor development, and cognitive function were normal. Adherence to metabolic formula and l-carnitine supplementation in Cohort I declined to 12% and 32%, respectively, by age 7 years. Cessation of strict dietary therapy altered plasma amino acid and carnitine concentrations but resulted in no serious adverse outcomes. In conclusion, neonatal diagnosis of GA1 coupled to management with lysine-free, arginine-enriched metabolic formula and emergency IV infusions during the first two years of life is safe and effective, preventing more than 90% of striatal injuries while supporting normal growth and psychomotor development. The need for dietary interventions and emergency IV therapies beyond early childhood is uncertain.

De Novo and Inherited Variants in GBF1 are Associated with Axonal Neuropathy Caused by Golgi Fragmentation

Distal hereditary motor neuropathies (HMNs) and axonal Charcot-Marie-Tooth neuropathy (CMT2) are clinically and genetically heterogeneous diseases characterized primarily by motor neuron degeneration and distal weakness. The genetic cause for about half of the individuals affected by HMN/CMT2 remains unknown. Here, we report the identification of pathogenic variants in GBF1 (Golgi brefeldin A-resistant guanine nucleotide exchange factor 1) in four unrelated families with individuals affected by sporadic or dominant HMN/CMT2. Genomic sequencing analyses in seven affected individuals uncovered four distinct heterozygous GBF1 variants, two of which occurred de novo. Other known HMN/CMT2-implicated genes were excluded. Affected individuals show HMN/CMT2 with slowly progressive distal muscle weakness and musculoskeletal deformities. Electrophysiological studies confirmed axonal damage with chronic neurogenic changes. Three individuals had additional distal sensory loss. GBF1 encodes a guanine-nucleotide exchange factor that facilitates the activation of members of the ARF (ADP-ribosylation factor) family of small GTPases. GBF1 is mainly involved in the formation of coatomer protein complex (COPI) vesicles, maintenance and function of the Golgi apparatus, and mitochondria migration and positioning. We demonstrate that GBF1 is present in mouse spinal cord and muscle tissues and is particularly abundant in neuropathologically relevant sites, such as the motor neuron and the growth cone. Consistent with the described role of GBF1 in Golgi function and maintenance, we observed marked increase in Golgi fragmentation in primary fibroblasts derived from all affected individuals in this study. Our results not only reinforce the existing link between Golgi fragmentation and neurodegeneration but also demonstrate that pathogenic variants in GBF1 are associated with HMN/CMT2.

Crigler-Najjar Syndrome Type 1: Pathophysiology, Natural History, and Therapeutic Frontier

BACKGROUND AND AIMS

We describe the pathophysiology, treatment, and outcome of Crigler-Najjar type 1 syndrome (CN1) in 28 UGT1A1 c.222C>A homozygotes followed for 520 aggregate patient-years.

APPROACH AND RESULTS

Unbound ("free") bilirubin (B_f ) was measured in patient sera to characterize the binding of unconjugated bilirubin (B_T ) to albumin (A) and validate their molar concentration ratio (B_T /A) as an index of neurological risk. Two custom phototherapy systems were constructed from affordable materials to provide high irradiance in the outpatient setting; light dose was titrated to keep B_T /A at least 30% below intravascular B_T binding capacity (i.e., B_T /A = 1.0). Categorical clinical outcomes were ascertained by chart review, and a measure (L_f ) was used to quantify liver fibrosis. Unbound bilirubin had a nonlinear relationship to B_T (R²  = 0.71) and B_T /A (R²  = 0.76), and B_f as a percentage of B_T correlated inversely to the bilirubin-albumin equilibrium association binding constant (R²  = 0.69), which varied 10-fold among individuals. In newborns with CN1, unconjugated bilirubin increased 4.3 ± 1.1 mg/dL per day. Four (14%) neonates developed kernicterus between days 14 and 45 postnatal days of life; peak B_T  ≥ 30 mg/dL and B_T /A ≥ 1.0 mol:mol were equally predictive of perinatal brain injury (sensitivity 100%, specificity 93.3%, positive predictive value 88.0%), and starting phototherapy after age 13 days increased this risk 3.5-fold. Consistent phototherapy with 33-103 µW/cm² •nm for 9.2 ± 1.1 hours/day kept B_T and B_T /A within safe limits throughout childhood, but B_T increased 0.46 mg/dL per year to reach dangerous concentrations by 18 years of age. Liver transplantation (n = 17) normalized B_T and eliminated phototherapy dependence. Liver explants showed fibrosis ranging from mild to severe.

CONCLUSION

Seven decades after its discovery, CN1 remains a morbid and potentially fatal disorder.

Branched-chain α-ketoacid dehydrogenase deficiency (maple syrup urine disease): Treatment, biomarkers, and outcomes

Over the past three decades, we studied 184 individuals with 174 different molecular variants of branched-chain α-ketoacid dehydrogenase activity, and here delineate essential clinical and biochemical aspects of the maple syrup urine disease (MSUD) phenotype. We collected data about treatment, survival, hospitalization, metabolic control, and liver transplantation from patients with classic (i.e., severe; n = 176), intermediate (n = 6) and intermittent (n = 2) forms of MSUD. A total of 13,589 amino acid profiles were used to analyze leucine tolerance, amino acid homeostasis, estimated cerebral amino acid uptake, quantitative responses to anabolic therapy, and metabolic control after liver transplantation. Standard instruments were used to measure neuropsychiatric outcomes. Despite advances in clinical care, classic MSUD remains a morbid and potentially fatal disorder. Stringent dietary therapy maintains metabolic variables within acceptable limits but is challenging to implement, fails to restore appropriate concentration relationships among circulating amino acids, and does not fully prevent cognitive and psychiatric disabilities. Liver transplantation eliminates the need for a prescription diet and safeguards patients from life-threatening metabolic crises, but is associated with predictable morbidities and does not reverse pre-existing neurological sequelae. There is a critical unmet need for safe and effective disease-modifying therapies for MSUD which can be implemented early in life. The biochemistry and physiology of MSUD and its response to liver transplantation afford key insights into the design of new therapies based on gene replacement or editing.

Homozygosity for a mutation affecting the catalytic domain of tyrosyl-tRNA synthetase (YARS) causes multisystem disease

Aminoacyl-tRNA synthetases (ARSs) are critical for protein translation. Pathogenic variants of ARSs have been previously associated with peripheral neuropathy and multisystem disease in heterozygotes and homozygotes, respectively. We report seven related children homozygous for a novel mutation in tyrosyl-tRNA synthetase (YARS, c.499C > A, p.Pro167Thr) identified by whole exome sequencing. This variant lies within a highly conserved interface required for protein homodimerization, an essential step in YARS catalytic function. Affected children expressed a more severe phenotype than previously reported, including poor growth, developmental delay, brain dysmyelination, sensorineural hearing loss, nystagmus, progressive cholestatic liver disease, pancreatic insufficiency, hypoglycemia, anemia, intermittent proteinuria, recurrent bloodstream infections and chronic pulmonary disease. Related adults heterozygous for YARS p.Pro167Thr showed no evidence of peripheral neuropathy on electromyography, in contrast to previous reports for other YARS variants. Analysis of YARS p.Pro167Thr in yeast complementation assays revealed a loss-of-function, hypomorphic allele that significantly impaired growth. Recombinant YARS p.Pro167Thr demonstrated normal subcellular localization, but greatly diminished ability to homodimerize in human embryonic kidney cells. This work adds to a rapidly growing body of research emphasizing the importance of ARSs in multisystem disease and significantly expands the allelic and clinical heterogeneity of YARS-associated human disease. A deeper understanding of the role of YARS in human disease may inspire innovative therapies and improve care of affected patients.

Recessive GM3 synthase deficiency: Natural history, biochemistry, and therapeutic frontier

GM3 synthase, encoded by ST3GAL5, initiates synthesis of all downstream cerebral gangliosides. Here, we present biochemical, functional, and natural history data from 50 individuals homozygous for a pathogenic ST3GAL5 c.862C>T founder allele (median age 8.1, range 0.7-30.5 years). GM3 and its derivatives were undetectable in plasma. Weight and head circumference were normal at birth and mean Apgar scores were 7.7 ± 2.0 (1 min) and 8.9 ± 0.5 (5 min). Somatic growth failure, progressive microcephaly, global developmental delay, visual inattentiveness, and dyskinetic movements developed within a few months of life. Infantile-onset epileptic encephalopathy was characterized by a slow, disorganized, high-voltage background, poor state transitions, absent posterior rhythm, and spike trains from multiple independent cortical foci; >90% of electrographic seizures were clinically silent. Hearing loss affected cochlea and central auditory pathways and 76% of children tested failed the newborn hearing screen. Development stagnated early in life; only 13 (26%) patients sat independently (median age 30 months), three (6%) learned to crawl, and none achieved reciprocal communication. Incessant irritability, often accompanied by insomnia, began during infancy and contributed to high parental stress. Despite catastrophic neurological dysfunction, neuroimaging showed only subtle or no destructive changes into late childhood and hospitalizations were surprisingly rare (0.2 per patient per year). Median survival was 23.5 years. Our observations corroborate findings from transgenic mice which indicate that gangliosides might have a limited role in embryonic neurodevelopment but become vital for postnatal brain growth and function. These results have critical implications for the design and implementation of ganglioside restitution therapies.

TNNT1 nemaline myopathy: natural history and therapeutic frontier

We describe the natural history of 'Amish' nemaline myopathy (ANM), an infantile-onset, lethal disease linked to a pathogenic c.505G>T nonsense mutation of TNNT1, which encodes the slow fiber isoform of troponin T (TNNT1; a.k.a. TnT). The TNNT1 c.505G>T allele has a carrier frequency of 6.5% within Old Order Amish settlements of North America. We collected natural history data for 106 ANM patients born between 1923 and 2017. Over the last two decades, mean age of molecular diagnosis was 16 ± 27 days. TNNT1 c.505G>T homozygotes were normal weight at birth but failed to thrive by age 9 months. Presenting neonatal signs were axial hypotonia, hip and shoulder stiffness, and tremors, followed by progressive muscle weakness, atrophy and contractures. Affected children developed thoracic rigidity, pectus carinatum and restrictive lung disease during infancy, and all succumbed to respiratory failure by 6 years of age (median survival 18 months, range 0.2-66 months). Muscle histology from two affected children showed marked fiber size variation owing to both Type 1 myofiber smallness (hypotrophy) and Type 2 fiber hypertrophy, with evidence of nemaline rods, myofibrillar disarray and vacuolar pathology in both fiber types. The truncated slow TNNT1 (TnT) fragment (p.Glu180Ter) was undetectable in ANM muscle, reflecting its rapid proteolysis and clearance from sarcoplasm. Similar functional and histological phenotypes were observed in other human cohorts and two transgenic murine models (Tnnt1-/- and Tnnt1 c.505G>T). These findings have implications for emerging molecular therapies, including the suitably of TNNT1 gene replacement for newborns with ANM or other TNNT1-associated myopathies.

Bi-allelic CCDC47 Variants Cause a Disorder Characterized by Woolly Hair, Liver Dysfunction, Dysmorphic Features, and Global Developmental Delay

Ca2+ signaling is vital for various cellular processes including synaptic vesicle exocytosis, muscle contraction, regulation of secretion, gene transcription, and cellular proliferation. The endoplasmic reticulum (ER) is the largest intracellular Ca2+ store, and dysregulation of ER Ca2+ signaling and homeostasis contributes to the pathogenesis of various complex disorders and Mendelian disease traits. We describe four unrelated individuals with a complex multisystem disorder characterized by woolly hair, liver dysfunction, pruritus, dysmorphic features, hypotonia, and global developmental delay. Through whole-exome sequencing and family-based genomics, we identified bi-allelic variants in CCDC47 that encodes the Ca2+-binding ER transmembrane protein CCDC47. CCDC47, also known as calumin, has been shown to bind Ca2+ with low affinity and high capacity. In mice, loss of Ccdc47 leads to embryonic lethality, suggesting that Ccdc47 is essential for early development. Characterization of cells from individuals with predicted likely damaging alleles showed decreased CCDC47 mRNA expression and protein levels. In vitro cellular experiments showed decreased total ER Ca2+ storage, impaired Ca2+ signaling mediated by the IP3R Ca2+ release channel, and reduced ER Ca2+ refilling via store-operated Ca2+ entry. These results, together with the previously described role of CCDC47 in Ca2+ signaling and development, suggest that bi-allelic loss-of-function variants in CCDC47 underlie the pathogenesis of this multisystem disorder.

Genomic diagnostics within a medically underserved population: efficacy and implications

PurposeWe integrated whole-exome sequencing (WES) and chromosomal microarray analysis (CMA) into a clinical workflow to serve an endogamous, uninsured, agrarian community.MethodsSeventy-nine probands (newborn to 49.8 years) who presented between 1998 and 2015 remained undiagnosed after biochemical and molecular investigations. We generated WES data for probands and family members and vetted variants through rephenotyping, segregation analyses, and population studies.ResultsThe most common presentation was neurological disease (64%). Seven (9%) probands were diagnosed by CMA. Family WES data were informative for 37 (51%) of the 72 remaining individuals, yielding a specific genetic diagnosis (n = 32) or revealing a novel molecular etiology (n = 5). For five (7%) additional subjects, negative WES decreased the likelihood of genetic disease. Compared to trio analysis, "family" WES (average seven exomes per proband) reduced filtered candidate variants from 22 ± 6 to 5 ± 3 per proband. Nineteen (51%) alleles were de novo and 17 (46%) inherited; the latter added to a population-based diagnostic panel. We found actionable secondary variants in 21 (4.2%) of 502 subjects, all of whom opted to be informed.ConclusionCMA and family-based WES streamline and economize diagnosis of rare genetic disorders, accelerate novel gene discovery, and create new opportunities for community-based screening and prevention in underserved populations.

Effects of genetic severity on glucose homeostasis in Friedreich ataxia

INTRODUCTION

Friedreich ataxia (FRDA) leads to increased risk of diabetes. Less is known regarding the dynamics of glucose homeostasis in FRDA, the influence of disease features, and the utility of oral-based metrics for capturing metabolic dysfunction.

METHODS

To examine these dynamics, we analyzed oral and intravenous glucose tolerance test data in 42 non-diabetic patients with FRDA.

RESULTS

Patients showed high insulin responsiveness to glucose and low insulin sensitivity. Genetic severity predicted overall metabolic impairment: individuals with longer guanine-adenine-adenine (GAA) repeats on the shorter allele showed a lower disposition index. Genetic severity did not predict any other variables. Measures of disposition index from intravenous and oral glucose tolerance testing did not correlate well, possibly reflecting divergent responses to oral and intravenous glucose loads.

CONCLUSIONS

FRDA patients demonstrate abnormal compensatory activity for managing glucose. Genetic severity impacts the global homeostatic profile, whereas relative contributions of insulin secretion and action vary from patient to patient. Muscle Nerve 54: 887-894, 2016.

Frataxin levels in peripheral tissue in Friedreich ataxia

Objective

Friedreich ataxia (FRDA) is an autosomal recessive ataxia resulting from mutations in the frataxin gene (FXN). Such mutations, usually expanded guanine–adenine–adenine (GAA) repeats, give rise to decreased levels of frataxin protein in both affected and unaffected tissues. The goal was to understand the relationship of frataxin levels in peripheral tissues to disease status.

Methods

Frataxin levels were measured in buccal cells and blood, and analyzed in relation to disease features. Site-directed mutant frataxin was also transfected into human embryonic kidney cells to model results from specific point mutations.

Results

There was no evidence for change in frataxin levels over time with repeated measures analysis, although linear regression analysis of cross-sectional data predicted a small increase over decades. GAA repeat length predicted frataxin levels in both tissues, and frataxin levels themselves predicted neurological ratings (accounting for age). Compound heterozygous patients for a GAA expansion and a point mutation in FXN generally had lower levels of frataxin than those homozygous for the presence of two GAA repeat expansions, though levels varied dramatically between tissues in some compound heterozygotes for point mutations. The G130V mutation led to decreased levels of frataxin in vitro as well as in vivo, while the R165C mutation produced normal immunoreactive levels of frataxin both in vitro and in vivo. Start codon mutations led to low levels of frataxin in buccal cells but preserved immunoreactive frataxin levels in blood.

Interpretation

The present data show that peripheral frataxin levels reflect disease features in FRDA, but emphasize the need for interpretation of such levels in the context of specific mutations.

Friedreich ataxia clinical outcome measures: natural history evaluation in 410 participants

Friedreich ataxia is an autosomal recessive neurodegenerative disorder characterized by ataxia, dysarthria, and areflexia. The authors report the progress of a large international noninterventional cohort (n = 410), tracking the natural history of disease progression using the neurologic examination-based Friedreich Ataxia Rating Scale. The authors analyzed the rate of progression with cross-sectional analysis and longitudinal analysis over a 2-year period. The Friedreich Ataxia Rating Scale captured disease progression when used at 1 and 2 years following initial evaluation, with a lower ratio of standard deviation of change to mean change over 2 years of evaluation. However, modeling of disease progression identified substantial ceiling effects in the Friedreich Ataxia Rating Scale, suggesting this measure is most useful in subjects before maximal deficit is approached.

Novel diagnostic paradigms for Friedreich ataxia

Friedreich ataxia is the most common inherited ataxia, with a wide phenotypic spectrum. It is generally caused by GAA expansions on both alleles of FXN, but a small percentage of patients are compound heterozygotes for a pathogenic expansion and a point mutation. Two recent diagnostic innovations are further characterizing individuals with the phenotype but without the classic genotypes. First, lateral-flow immunoassay is able to quantify the frataxin protein, thereby further characterizing these atypical individuals as likely affected or not affected, and providing some correlation to phenotype. It also holds promise as a biomarker for clinical trials in which the investigative agent increases frataxin. Second, gene dosage analysis and the identification of affected individuals with gene deletions introduce a novel genetic mechanism of disease. Both tests are now clinically available and suggest a new diagnostic paradigm for the disorder. Genetic counseling issues and future diagnostic testing approaches are considered as well.

A0001 in Friedreich ataxia: biochemical characterization and effects in a clinical trial

This study tested the ability of A0001 (α-tocopheryl quinone; EPI-A0001), a potent antioxidant, to improve in vitro measures, glucose metabolism, and neurological function in Friedreich ataxia. We used an in vitro study of protection from cell toxicity followed by a double-blind, randomized, placebo-controlled trial of 2 doses of A0001 in 31 adults with Friedreich ataxia. The primary clinical trial outcome was the Disposition Index, a measure of diabetic tendency, from a frequently sampled intravenous glucose tolerance test, evaluated 4 weeks into therapy. Secondary neurologic measures included the Friedreich Ataxia Rating Scale. A0001 potently inhibited cell death in Friedreich ataxia models in vitro. For the clinical trial, mean guanine-adenine-adenine repeat length was 699, and mean age was 31 years. Four weeks after treatment initiation, differences in changes in the Disposition Index between subjects treated with A0001 and placebo were not statistically significant. In contrast, a dose-dependent improvement in the Friedreich Ataxia Rating Scale score was observed. Patients on placebo improved 2.0 rating scale points, whereas patients on low-dose A0001 improved by 4.9 points (P = .04) and patients on a high dose improved by 6.1 points (P < .01). Although A0001 did not alter the Disposition Index, it caused a dose-dependent improvement in neurologic function, as measured by the Friedreich Ataxia Rating Scale. Longer studies will assess the reproducibility and persistence of neurologic benefit.

First-trimester screening for aneuploidy

Prenatal screening for aneuploidy in the first trimester using novel ultrasound and maternal serum markers represents a promising improvement over the currently available second-trimester screening methods. This article reviews the current status of first-trimester screening for Down syndrome and other aneuploidies and explores the issues related to implementing first-trimester screening into mainstream prenatal care in the United States.