Propionic acidemia is an inborn error of metabolism involving an enzymatic defect of propionyl-CoA carboxylase that results in the build-up of toxic metabolites which can induce metabolic decompensation. Secondary mitochondrial dysfunction in propionic acidemia has been commonly recognized; however, its clinical presentation and management are not well represented in literature. Here, we present a case of profound hyperglycemia and lactic acidosis without hyperammonemia in a propionic acidemia patient, where medical management incorporated mitochondrial dysfunction via a brief reduction in glucose infusion rate. We review the literature on propionic acidemia and mitochondrial dysfunction in an effort to provide a tangible clinical case where considerations of mitochondrial dysfunction were made to guide further decision making in taking care of this patient population.

Genomic reanalysis can identify causative variants for rare diseases as patient phenotypes evolve and gene-disease knowledge expands. Despite its diagnostic value, routine reanalysis is limited by clinician capacity, lack of patient follow-up, data silos, cost, and lack of availability of clinical data to testing laboratories that are not obligated to conduct reanalysis. The Children’s Rare Disease Collaborative at Boston Children’s Hospital (BCH) has integrated genomic and phenotypic data from over 15,500 patients into a clinician-facing platform. Leveraging this infrastructure, we developed a Proactive Genomic Reanalysis (PGR) workflow at BCH for clinical sequencing data that is centralized, semi-automated, and clinically integrated. Here, we report initial results and outline required resources and transferable insights applicable to other healthcare settings. Initial pilot implementation, applied to a subset of clinical sequencing patients’ data, revealed practical challenges, notably clinician turnover and patient recontact difficulties. Of 42 patients’ candidate variants discovered by the PGR bioinformatics pipeline and returned to treating clinicians, 33 were determined to have a high suspicion of disease causality and an additional 3 were determined to be candidate variant of uncertain significance. A process to generate reports and return results to patients was initiated when applicable. Although the initial pilot implementation was limited, the PGR bioinformatics pipeline is designed to be utilized iteratively, making reanalysis a continuing process. This work highlights the feasibility and impact of centralized PGR processes and the potential for healthcare institutions to scale genomic reanalysis.

BACKGROUND:CLPB-related mitochondrial disease causes congenital neutropenia, developmental delay/intellectual disability, progressive brain atrophy, movement disorders, cataracts, and 3-methylglutaconic aciduria. Both monoallelic and biallelic forms exist. This retrospective cohort study compared clinical outcomes and genotype-structure-phenotype correlations across zygosity groups. METHODS:Sixty-three individuals (41 biallelic, 22 monoallelic; 6 unpublished) with disease-causing CLPB variants were identified via literature review and a multicenter survey. In silico modeling assessed structural impact. A modified CLPB Disease Burden Index (DBI) quantified severity. RESULTS:Median age at last follow-up was 4.0 years (IQR: 0.25-12.6) in biallelic and 12.0 years (IQR: 5.3-21.0) in monoallelic cases. Death occurred in 66% of biallelic and 23% of monoallelic individuals, with earlier median age at death in biallelic cases (6 months vs 2.4 years). Biallelic cases had significantly higher DBI scores and poorer survival (4-year survival: 50% vs 82%). Stop/stop genotypes were associated with greater disease burden than missense combinations. Structural predictions-particularly variants causing nonsense-mediated decay or ankyrin domain disruption-were stronger survival predictors than zygosity or age of onset. Early-onset disease (<12 months) correlated with more severe progression. Later onset often resulted in milder phenotypes. Hematologic and neurologic features overlapped across zygosity; cataracts and dystonia were more common in biallelic cases. Milestone attainment was poor, with <50% walking or speaking, and only 10-20% doing so on time. Four monoallelic patients received hematopoietic stem cell transplants with mixed outcomes. Granulocyte colony-stimulating factor was associated with improved survival. CONCLUSIONS:This is the largest cohort study to date comparing biallelic and monoallelic CLPB deficiency. Structural variant impact-particularly ankyrin domain disruption-emerged as a key prognostic factor.

Smith-Lemli-Opitz syndrome (SLOS), also known as RSH syndrome, is an inborn error of cholesterol biosynthesis first described in 1964. Since then, significant advances have been made in understanding its pathophysiology, both during fetal development and postnatally. Cholesterol is a crucial lipid in the body, especially in the central nervous system, which accounts for nearly 25% of the body's total cholesterol. Cholesterol deficiency in SLOS can lead to congenital malformations and severe neurodevelopmental disabilities. The biochemical and genetic bases of SLOS have been elucidated. Reduced or absent 7-dehydrocholesterol reductase enzymatic activity results not only in cholesterol deficiency but also in accumulation of 7-dehydrocholesterol, 8-dehydrocholesterol, and toxic oxysterol metabolites, which contribute to the pathophysiology of SLOS and correlate variably with the severity of its clinical symptoms. Despite decades of research, the clinical recognition of SLOS remains challenging because of the condition's multisystemic nature and noteworthy phenotypic variability. This review provides an up-to-date summary of major research advances in the study of SLOS with a focus on clinical manifestations and biochemical and genetic findings, which, taken together, facilitate recognition and diagnostic confirmation. Additionally, we recap past and current efforts in therapeutic development and offer guidance for disease management.

BACKGROUND AND OBJECTIVES:The NALCN channelosome regulates the resting membrane potential through sodium leak currents, influencing cellular excitability. Genetic variants in NALCN and UNC80, a subunit of the NALCN channelosome, cause ultra-rare and severe neurodevelopmental disorders. Autosomal dominant congenital contractures of the limbs and face, hypotonia, and developmental delay (CLIFAHDD) syndrome is associated with gain-of-function (GOF) variants in NALCN. Infantile hypotonia with psychomotor retardation and characteristic facies (IHPRF) 1 syndrome is associated with biallelic variants in NALCN and IHPRF 2 syndrome with biallelic variants in UNC80, both resulting in a loss-of-function (LOF). This study aims to expand the phenotypes associated with these syndromes, exploring potential genotype-phenotype associations. METHODS:This is a cross-sectional study including patients with pathogenic or likely pathogenic variants in NALCN and UNC80. Phenotypes were evaluated through a structured interview, questionnaires, and review of medical records. Associations between variants, clinical features, and syndromes were analyzed. RESULTS:Fifty-one patients were included (34 with CLIFAHDD, 9 with IHPRF 1, 8 with IHPRF 2; 3 months-27 years; 37.3% female). All exhibited neurodevelopmental delay, more severe in patients with LOF variants (p = 0.019). Neurodevelopmental regression was observed in 29.4% of patients with CLIFAHDD syndrome, associated with the onset of ataxia (70%). Patients with CLIFAHDD had more severe respiratory symptoms at birth (11.7% orotracheal intubation). Distal arthrogryposis (76.5%), episodic ataxia (41.2% of ambulatory patients), and paroxysmal dystonia (11.7%) were exclusively diagnosed in patients with CLIFAHDD. Patients with LOF variants presented more frequently with failure to thrive (88.2%, p = 0.001), central sleep apnea (CSA, 64.7%, p < 0.001), and epilepsy (70.6%, p < 0.001). Epilepsy was associated with more severe cognitive delays (p = 0.016) and was refractory in 58.8% of patients. Earlier seizure onset was associated with refractory epilepsy (p = 0.014). Patients with CLIFAHDD and premature death, epilepsy, or paroxysmal dystonia carried variants within NALCN pore domains. DISCUSSION:This study provides an in-depth clinical characterization of NALCN-related and UNC80-related disorders. Distal arthrogryposis, episodic ataxia, and paroxysmal dystonia were diagnosed in patients with CLIFAHDD while failure to thrive, CSA, and epilepsy were associated with LOF variants. We suggest potential genotype-phenotype associations, formulating hypotheses for validation in future studies with larger cohorts.

Smith-Lemli-Opitz Syndrome (SLOS) is an autosomal recessive disorder of cholesterol biosynthesis caused by biallelic pathogenic variants in DHCR7, which encodes the enzyme 7-dehydrocholesterol reductase (DHCR7). SLOS is a multisystemic disorder affecting various aspects of health, including growth, development, behavior, and quality of life, underscoring the need for safe, efficacious interventions that limit disease burden. DHCR7 enzyme deficiency leads to a “metabolic block” resulting in decreased cholesterol production and accumulation of its precursor 7-dehydrocholesterol and the secondary isomer 8-dehydrocholesterol. Reduced cholesterol synthesis, in turn, leads to decreased levels of cholic acid (CA), an endogenous bile acid synthesized from cholesterol and essential for cholesterol absorption. Dietary cholesterol supplementation is standard therapy. Bile acid supplementation with CA has been shown to improve dietary cholesterol absorption and raise plasma cholesterol levels. However, there is a paucity of patient-level data regarding the utility of CA as a treatment for SLOS. The purpose of this case series is to address the lack of comprehensive patient data through documentation of the outcomes of a company-sponsored CA patient experience program. A retrospective chart review was conducted for these individuals while on CA plus cholesterol supplementation. Data for demographics and key clinical/laboratory parameters were captured with a standardized data collection tool. Eight genetically confirmed individuals with SLOS (age range 1 to 20 years) with median plasma cholesterol levels at baseline ≤ 125 mg/dL were treated with CA at 10–15 mg/kg/d for 30 to 450 days. Exogenous CA administration improved cholesterol levels in the majority of patients. Growth improved after CA initiation and trended toward age-appropriate growth percentiles. Reports from the patient, parent/caregiver, and/or healthcare professional noted positive behavioral changes leading to increased social interaction, cognitive engagement, and improved communication skills. Improvements in biochemical parameters and quality of life were also observed in several patients after CA treatment. CA supplementation was well tolerated with minimal adverse events. The cumulative experiences of eight patients provide a compelling narrative supporting the potential utility of CA treatment in SLOS while underscoring the safety of CA in this patient population. Larger longitudinal studies of CA in patients with SLOS are warranted.

Pyruvate dehydrogenase complex deficiency (PDCD) is a mitochondrial disorder of carbohydrate oxidation characterized by lactic acidosis and central nervous system involvement. Knowledge of the affected metabolic pathways and clinical observations suggest that early initiation of the ketogenic diet may ameliorate the metabolic and neurologic course of the disease. We present a case in which first trimester ultrasound identified structural brain abnormalities prompting a prenatal molecular diagnosis of PDCD. Ketogenic diet, thiamine, and N-acetylcysteine were initiated in the perinatal period with good response, including sustained developmental progress. This case highlights the importance of a robust neurometabolic differential diagnosis for prenatally diagnosed structural anomalies and the use of prenatal molecular testing to facilitate rapid, genetically tailored intervention.

Primary proteasomopathies have recently emerged as a new class of rare early-onset neurodevelopmental disorders (NDDs) caused by pathogenic variants in the PSMB1, PSMC1, PSMC3, or PSMD12 proteasome genes. Proteasomes are large multi-subunit protein complexes that maintain cellular protein homeostasis by clearing ubiquitin-tagged damaged, misfolded, or unnecessary proteins. In this study, we have identified PSMD11 as an additional proteasome gene in which pathogenic variation is associated with an NDD-causing proteasomopathy. PSMD11 loss-of-function variants caused early-onset syndromic intellectual disability and neurodevelopmental delay with recurrent obesity in 10 unrelated children. Our findings demonstrate that the cognitive impairment observed in these individuals could be recapitulated in Drosophila melanogaster with depletion of the PMSD11 ortholog Rpn6, which compromised reversal learning. Our investigations in subject samples further revealed that PSMD11 loss of function resulted in impaired 26S proteasome assembly and the acquisition of a persistent type I interferon (IFN) gene signature, mediated by the integrated stress response (ISR) protein kinase R (PKR). In summary, these data identify PSMD11 as an additional member of the growing family of genes associated with neurodevelopmental proteasomopathies and provide insights into proteasomal biology in human health.

Acute liver failure is rare in the neonatal and infant population; however, when encountered, it requires timely diagnosis, management, and identification of the underlying etiology to provide the best clinical outcomes. Here, we present a case of new-onset liver failure in a 4-month-old infant. She had previously been diagnosed with neonatal mucocutaneous herpes simplex virus disease, but had been healthy in the interval, and was referred to our hospital for evaluation of possible need for liver transplantation because of a rapidly progressing pace of disease. In this diagnostic dilemma article, we review the case history and presentation and consider the differential diagnosis from the points of view of the primary and consultative teams. We then follow the clinical evolution of disease, identify a final diagnosis, and explore the short- and long-term management and health implications of the diagnosis. This case should be of interest to primary care providers, intensivists who care for neonates or infants, and specialists who encounter liver failure in their clinical practice.

Developmental and epileptic encephalopathies (DEEs) feature altered brain development, developmental delay and seizures, with seizures exacerbating developmental delay. Here we identify a cohort with biallelic variants in DENND5A, encoding a membrane trafficking protein, and develop animal models with phenotypes like the human syndrome. We demonstrate that DENND5A interacts with Pals1/MUPP1, components of the Crumbs apical polarity complex required for symmetrical division of neural progenitor cells. Human induced pluripotent stem cells lacking DENND5A fail to undergo symmetric cell division with an inherent propensity to differentiate into neurons. These phenotypes result from misalignment of the mitotic spindle in apical neural progenitors. Cells lacking DENND5A orient away from the proliferative apical domain surrounding the ventricles, biasing daughter cells towards a more fate-committed state, ultimately shortening the period of neurogenesis. This study provides a mechanism for DENND5A-related DEE that may be generalizable to other developmental conditions and provides variant-specific clinical information for physicians and families. Developmental and epileptic encephalopathies are devastating neurological disorders. Here, the authors establish a cohort of patients with variants in the gene DENND5A and use human stem cells to discover a disease mechanism involving altered cell division.

Major clinical events (MCEs) related to long-chain fatty acid oxidation disorders (LC-FAOD) in triheptanoin clinical trials include inpatient or emergency room (ER) visits for three major clinical manifestations: rhabdomyolysis, hypoglycemia, and cardiomyopathy. However, outcomes data outside of LC-FAOD clinical trials are limited. The non-interventional cohort LC-FAOD Odyssey study examines data derived from US medical records and patient reported outcomes to quantify LC-FAOD burden according to management strategy including MCE frequency and healthcare resource utilization (HRU).Thirty-four patients were analyzed of which 21 and 29 patients had received triheptanoin and/or medium chain triglycerides (MCT), respectively. 36% experienced MCEs while receiving triheptanoin versus 54% on MCT. Total mean annualized MCE rates on triheptanoin and MCT were 0.1 and 0.7, respectively. Annualized disease-related inpatient and ER events were lower on triheptanoin (0.2, 0.3, respectively) than MCT (1.2, 1.0, respectively). Patients were managed more in an outpatient setting on triheptanoin (8.9 annualized outpatient visits) vs MCT (7.9). Overall, this shows that those with LC-FAOD in the Odyssey program experienced fewer MCEs and less HRU in inpatient and ER settings during triheptanoin-treated periods compared with the MCT-treated periods. The MCE rate was lower after initiation of triheptanoin, consistent with clinical trials.

BACKGROUND:Identifying a precise genetic diagnosis can improve outcomes for individuals with rare disease, though the resources required to do so may impede access and exacerbate healthcare disparities leading to inequitable care. Our objective was therefore to determine the effect of multiple sociodemographic factors on the yield of the diagnostic evaluation for genetics outpatients.METHODS:This is a retrospective cohort study from 2017 to 2019 of outpatient genetics referrals at a pediatric academic tertiary care center. Exposures included: primary language, insurance type, and neighborhood resources (via the Childhood Opportunity Index, COI). The primary outcome was identification of a genetic diagnosis within 2 years of the initial clinic visit.RESULTS:COI quintile was not significantly associated with the odds of diagnosis but was significantly associated with clinic attendance, with lower neighborhood resources leading to incomplete referrals. Limited English proficiency was associated with a higher odds of diagnosis, though at an older age. Public insurance was associated with increased access to genetic testing.CONCLUSIONS:Lower neighborhood resources are negatively associated with clinic attendance. Our findings further suggest delays in care and a referral bias for more severe phenotypes among families with limited English proficiency. Improved access to clinical genetics is needed to improve diagnostic equity.IMPACT:The resources required to identify a genetic diagnosis may impede access and exacerbate healthcare disparities leading to inequitable care. In an analysis of pediatric outpatient genetics referrals, we observed a significant association between neighborhood resources and clinic attendance but not diagnostic yield for those attending, and a higher diagnostic yield for families with limited English proficiency, suggesting referral bias for more severe phenotypes. Thus, the primary barrier to finding a genetic diagnosis was initiation of care, not the ensuing diagnostic odyssey. Further research efforts should be directed at increasing access to clinical genetics evaluations for children with rare disease.