Family Lore, a Variant of Uncertain Significance, and CADASIL.

An infant presents in extremis. After the medical team stabilizes him, the race is on to figure out why he got so sick in the first place. The consulting genetics team thinks that it is unlikely his problems are due to a genetic cause, but his extreme, confounding presentation is enough to justify trio exome sequencing. When the results reveal an unexpected, paternally inherited variant of uncertain significance (VUS) in NOTCH3, fresh questions arise. The infant's presenting symptoms and descriptive diagnoses, including hematemesis, epistaxis, and gastric ulcers, certainly do not fit the mold of CADASIL. However, closer inspection of his family history yields tantalizing clues: a father and paternal grandfather with seizures, and a paternal grandfather with unexplained mood disturbances in middle age. Combining details gleaned from the family history and medical literature, the clinical genetics and laboratory genetics team collaborated, reclassified the VUS as likely pathogenic, and offered a new unifying diagnosis to explain much of the family's lore.

Clinical exome sequencing uncovers genetic disorders in neonates with suspected hypoxic-ischemic encephalopathy: A retrospective analysis.

Hypoxic-ischemic encephalopathy (HIE) occurs in up to 7 out of 1000 births and accounts for almost a quarter of neonatal deaths worldwide. Despite the name, many newborns with HIE have little evidence of perinatal hypoxia. We hypothesized that some infants with HIE have genetic disorders that resemble encephalopathy. We reviewed genetic results for newborns with HIE undergoing exome or genome sequencing at a clinical laboratory (2014-2022). Neonates were included if they had a diagnosis of HIE and were delivered ≥35 weeks. Neonates were excluded for cardiopulmonary pathology resulting in hypoxemia or if neuroimaging suggested postnatal hypoxic-ischemic injury. Of 24 patients meeting inclusion criteria, six (25%) were diagnosed with a genetic condition. Four neonates had variants at loci linked to conditions with phenotypic features resembling HIE, including KIF1A, GBE1, ACTA1, and a 15q13.3 deletion. Two additional neonates had variants in genes not previously associated with encephalopathy, including DUOX2 and PTPN11. Of the six neonates with a molecular diagnosis, two had isolated HIE without apparent comorbidities to suggest a genetic disorder. Genetic diagnoses were identified among neonates with and without sentinel labor events, abnormal umbilical cord gasses, and low Apgar scores. These results suggest that genetic evaluation is clinically relevant for patients with perinatal HIE.

MED12 Loss-of-Function Variants as a Cause of Congenital Diaphragmatic Hernia in Females With Hardikar Syndrome and Nonspecific Intellectual Disability.

Mediator complex subunit 12 (MED12) is required for the assembly of the kinase module of Mediator, a regulatory complex that controls the formation of the RNA polymerase II-mediated preinitiation complex. MED12-related disorders display unique gender-specific genotype-phenotype associations and include X-linked recessive Opitz-Kaveggia syndrome, Lujan-Fryns syndrome, Ohdo syndrome, and nonspecific intellectual disability in males predominantly carrying missense variants, and X-linked dominant Hardikar syndrome and nonspecific intellectual disability in females known to predominantly carry de novo nonsense/frameshift and nonsense/missense variants, respectively. MED12 was previously identified as a low-penetrance candidate gene for non-isolated congenital diaphragmatic hernia (CDH+). At the time, however, there was insufficient evidence to confirm this association. In a clinical database search, we identified 18 individuals who were molecularly diagnosed with MED12-related disorders by exome or genome sequencing, including eight missense, four frameshift, two nonsense, and one splice variant. Nine of these variants have not been previously reported. Two females with nonspecific intellectual disability were found to carry a de novo frameshift variant, indicating that potentially truncating variants causing nonspecific intellectual disability are not limited to nonsense variants. Notably, CDH was reported in three out of seven females with Hardikar syndrome or nonspecific intellectual disability but was not reported in males with MED12-related disorders. These results suggest that pathogenic MED12 variants are a cause of CDH+ in females with Hardikar syndrome and nonspecific intellectual disability.

Heteroplasmic pathogenic m.12315G>A variant in MT-TL2 presenting with MELAS syndrome and depletion of nitric oxide donors.

The MT-TL2 m.12315G>A pathogenic variant has previously been reported in five individuals with mild clinical phenotypes. Herein we report the case of a 5-year-old child with heteroplasmy for this variant who developed neurological regression and stroke-like episodes similar to those observed in mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS). Biochemical evaluation revealed depletion of arginine on plasma amino acid analysis and low z-scores for citrulline on untargeted plasma metabolomics analysis. These findings suggested that decreased availability of nitric oxide may have contributed to the stroke-like episodes. The use of intravenous arginine during stroke-like episodes and daily enteral L-citrulline supplementation normalized her biochemical values of arginine and citrulline. Untargeted plasma metabolomics showed the absence of nicotinamide and 1-methylnicotinamide, and plasma total glutathione levels were low; thus, nicotinamide riboside and N-acetylcysteine therapies were initiated. This report expands the phenotype associated with the rare mitochondrial variant MT-TL2 m.12315G>A to include neurological regression and a MELAS-like phenotype. Individuals with this variant should undergo in-depth biochemical analysis to include untargeted plasma metabolomics, plasma amino acids, and glutathione levels to help guide a targeted approach to treatment.

Intracranial calcifications simulating Aicardi-Goutières syndrome in PARS2-related mitochondrial disease.

PARS2 encodes an aminoacyl-tRNA synthetase that catalyzes the ligation of proline to mitochondrial prolyl-tRNA molecules. Diseases associated with PARS2 primarily affect the central nervous system, causing early infantile developmental epileptic encephalopathies (EIDEE; DEE75; MIM #618437) with infantile-onset neurodegeneration. Dilated cardiomyopathy has also been reported in the affected individuals. About 10 individuals to date have been described with pathogenic biallelic variants in PARS2. While many of the reported individuals succumbed to the disease in the first two decades of life, autopsy findings have not yet been reported. Here, we describe neuropathological findings in a deceased male with evidence of intracranial calcifications in the basal ganglia, thalamus, cerebellum, and white matter, similar to Aicardi-Goutières syndrome. This report describes detailed autopsy findings in a child with PARS2-related mitochondrial disease and provides plausible evidence that intracranial calcifications may be a previously unrecognized feature of this disorder.

Expanded clinical phenotype and untargeted metabolomics analysis in RARS2-related mitochondrial disorder: a case report.

BACKGROUND: RARS2-related mitochondrial disorder is an autosomal recessive mitochondrial encephalopathy caused by biallelic pathogenic variants in the gene encoding the mitochondrial arginyl-transfer RNA synthetase 2 (RARS2, MIM *611524, NM_020320.5). RARS2 catalyzes the transfer of L-arginine to its cognate tRNA during the translation of mitochondrially-encoded proteins. The classical presentation of RARS2-related mitochondrial disorder includes pontocerebellar hypoplasia (PCH), progressive microcephaly, profound developmental delay, feeding difficulties, and hypotonia. Most patients also develop severe epilepsy by three months of age, which consists of focal or generalized seizures that frequently become pharmacoresistant and lead to developmental and epileptic encephalopathy (DEE). CASE PRESENTATION: Here, we describe a six-year-old boy with developmental delay, hypotonia, and failure to thrive who developed an early-onset DEE consistent with Lennox-Gastaut Syndrome (LGS), which has not previously been observed in this disorder. He had dysmorphic features including bilateral macrotia, overriding second toes, a depressed nasal bridge, retrognathia, and downslanting palpebral fissures, and he did not demonstrate progressive microcephaly. Whole genome sequencing identified two variants in RARS2, c.36 + 1G > T, a previously unpublished variant that is predicted to affect splicing and is, therefore, likely pathogenic and c.419 T > G (p.Phe140Cys), a known pathogenic variant. He exhibited significant, progressive generalized brain atrophy and ex vacuo dilation of the supratentorial ventricular system on brain MRI and did not demonstrate PCH. Treatment with a ketogenic diet (KD) reduced seizure frequency and enabled him to make developmental progress. Plasma untargeted metabolomics analysis showed increased levels of lysophospholipid and sphingomyelin-related metabolites. CONCLUSIONS: Our work expands the clinical spectrum of RARS2-related mitochondrial disorder, demonstrating that patients can present with dysmorphic features and an absence of progressive microcephaly, which can help guide the diagnosis of this condition. Our case highlights the importance of appropriate seizure phenotyping in this condition and indicates that patients can develop LGS, for which a KD may be a viable therapeutic option. Our work further suggests that analytes of phospholipid metabolism may serve as biomarkers of mitochondrial dysfunction.

Clinical genome sequencing: Three years' experience at a tertiary children's hospital.

PURPOSE: Genome sequencing (GS) may shorten the diagnostic odyssey for patients, but clinical experience with this assay in nonresearch settings remains limited. Texas Children's Hospital began offering GS as a clinical test to admitted patients in 2020, providing an opportunity to study GS utilization, possibilities for test optimization, and testing outcomes. METHODS: We retrospectively reviewed GS orders for admitted patients for a nearly 3-year period from March 2020 through December 2022. We gathered anonymized clinical data from the electronic health record to answer the study questions. RESULTS: The diagnostic yield over 97 admitted patients was 35%. The majority of GS clinical indications were neurologic or metabolic (61%) and most patients were in intensive care (58%). Tests were often characterized as candidates for intervention/improvement (56%), frequently because of redundancy with prior testing. Patients receiving GS without prior exome sequencing (ES) had higher diagnostic rates (45%) than the cohort as a whole. In 2 cases, GS revealed a molecular diagnosis that is unlikely to be detected by ES. CONCLUSION: The performance of GS in clinical settings likely justifies its use as a first-line diagnostic test, but the incremental benefit for patients with prior ES may be limited.

Genetic counseling in diabetes mellitus: A practice resource of the National Society of Genetic Counselors.

Diabetes mellitus is a group of diseases characterized by hyperglycemia and its consequences, affecting over 34 million individuals in the United States and 422 million worldwide. While most diabetes is polygenic and is classified as type 1 (T1D), type 2 (T2D), or gestational diabetes (GDM), at least 0.4% of all diabetes is monogenic in nature. Correct diagnosis of monogenic diabetes has important implications for glycemic management and genetic counseling. We provide this Practice Resource to familiarize the genetic counseling community with (1) the existence of monogenic diabetes, (2) how it differs from more common polygenic/complex diabetes types, (3) the advantage of a correct diagnosis, and (4) guidance for identifying, counseling, and testing patients and families with suspected monogenic diabetes. This document is intended for genetic counselors and other healthcare professionals providing clinical services in any setting, with the goal of maximizing the likelihood of a correct diagnosis of monogenic diabetes and access to related care.

NAXE deficiency: A neurometabolic disorder of NAD(P)HX repair amenable for metabolic correction.

The NAD(P)HX repair system is a metabolite damage repair mechanism responsible for restoration of NADH and NADPH after their inactivation by hydration. Deficiency in either of its two enzymes, NAD(P)HX dehydratase (NAXD) or NAD(P)HX epimerase (NAXE), causes a fatal neurometabolic disorder characterized by decompensations precipitated by inflammatory stress. Clinical findings include rapidly progressive muscle weakness, ataxia, ophthalmoplegia, and motor and cognitive regression, while neuroimaging abnormalities are subtle or nonspecific, making a clinical diagnosis challenging. During stress, nonenzymatic conversion of NAD(P)H to NAD(P)HX increases, and in the absence of repair, NAD(P)H is depleted, and NAD(P)HX accumulates, leading to decompensation; however, the contribution of each to the metabolic derangement is not established. Herein, we summarize the clinical knowledge of NAXE deficiency from 30 cases and lessons learned about disease pathogenesis from cell cultures and model organisms and describe a metabolomics signature obtained by untargeted metabolomics analysis in one case at the time of crisis and after initiation of treatment. Overall, biochemical findings support a model of acute depletion of NAD+, signs of mitochondrial dysfunction, and altered lipidomics. These findings are further substantiated by untargeted metabolomics six months post-crisis showing that niacin supplementation reverses primary metabolomic abnormalities concurrent with improved clinical status.

A phenotypic expansion of TRNT1 associated sideroblastic anemia with immunodeficiency, fevers, and developmental delay.

Sideroblastic anemia with immunodeficiency, fevers, and developmental delay (SIFD; MIM #616084) is an autosomal recessive disorder of mitochondrial and cytosolic tRNA processing caused by pathogenic, biallelic variants in TRNT1. Other features of this disorder include central nervous system, renal, cardiac, ophthalmological features, and sensorineural hearing impairment. SIFD was first described in 2013 and to date, it has been reported in 46 patients. Herein, we review the literature and describe two siblings with SIFD and note the novel phenotype of hypoglycemia in the context of growth hormone (GH) deficiency. GH deficiency without hypoglycemia has previously been reported in three patients with SIFD, but GH deficiency had not been firmly ascribed to SIFD. We propose to expand the phenotype to include GH deficiency, hypoglycemia, and previously unreported dysmorphic features. Furthermore, we highlight the intrafamilial variability of the disease by the discordance of our patients' clinical phenotypes and biochemical profiles measured by untargeted metabolomics analysis. Several metabolomic abnormalities were observed in both patients, and these may represent a potential biochemical signature for SIFD.

Characterization of genetic counselor practices in inpatient care settings.

Rapid genomic testing is increasingly used in inpatient settings for diagnostic and treatment purposes. With the expansion of genetic testing in this setting, requests for inpatient genetics consultations have increased. There have been reports of genetic counselors working in inpatient care, though their specific roles are not well described. In this study, we characterized the roles of genetic counselors practicing in inpatient care settings in the United States and Canada. Genetic counselors were recruited via professional organization listservs to complete an online survey. The survey gathered information on participants' roles and workflow of inpatient genetics consultation services at their institution. Responses from 132 participants demonstrate that 50.4% of genetic counselors cover genetics consultations as needed or on a rotating schedule (34.6%). They practice in general pediatric (59.1%), neonatal (42.5%), cancer (28.3%), and/or prenatal (18.9%) specialties, among others. Participants reported working independently (16.1%) or with other providers (54.8%), including geneticists and other attending physicians. The workflow of genetics consultation services varies between institutions in the delivery of consults, members of the inpatient genetics consultation care team, and administrative support. Fifty percent of participants reported having no exposure to inpatients during graduate training, and 87.3% of participants reported receiving no institutional training for their inpatient role. This is the first study to describe roles of genetic counselors in inpatient care. It establishes a foundation for future research on inpatient genetic counseling and genetic counseling outcomes in inpatient services. As demand for genetics expertise in inpatient care grows, genetic counselors can be hired to serve inpatient populations alongside genetics and non-genetics providers.

Sudden infant death with dysgenesis of the testes syndrome in a non-Amish infant: A case report.

Sudden Infant Death with Dysgenesis of the Testes syndrome (SIDDT) is a very rare condition associated with biallelic pathogenic variants in the TSPYL1 gene first reported in 2004. It is characterized by sudden cardiac or respiratory arrest, disordered testicular development, neurologic dysfunction, and is uniformly fatal before the age of 12 months. There were previously 21 reported cases of SIDDT in the literature, all from nine Old Order Amish families published in a single paper. In this report, we describe a non-Amish, phenotypically female infant with poor feeding and abnormal motor movements noted at birth. Initial testing showed that she had a 46,XY chromosome complement, and chromosomal microarray showed a significant absence of heterozygosity (AOH) totalling roughly 600 Mb across multiple different chromosomes, indicating consanguinity. Further workup with exome sequencing revealed homozygosity for a frameshift variant in TSPYL1 (c.725_726delTG, p.Val242GlufsTer52) consistent with a diagnosis of SIDDT, explaining many of her clinical features. However, she was also noted to have a mild T-cell lymphopenia and developed intractable epilepsy after hospital discharge. These features have not previously been reported in SIDDT and may represent phenotypic expansion. To our knowledge, this patient is the 22nd case of SIDDT to be reported in the literature, and the first to be of non-Amish heritage.

Multiple mitochondrial dysfunctions syndrome 1: An unusual cause of developmental pulmonary hypertension.

Pulmonary hypertension (pHTN) is a severe, life-threatening disease, which can be idiopathic or associated with an underlying syndrome or genetic diagnosis. Here we discuss a patient who presented with severe pHTN and was later found to be compound heterozygous for pathogenic variants in the NFU1 gene causing multiple mitochondrial dysfunctions syndrome 1 (MMDS1). Review of autopsy slides from an older sibling revealed the same diagnosis along with pulmonary findings consistent with a developmental lung disorder. In particular, these postmortem, autopsy findings have not been described previously in humans with this mitochondrial syndrome and suggest a possible developmental basis for the severe pHTN seen in this disease. Given the rarity of patients reported with MMDS1, we review the current state of knowledge of this disease and our novel management strategies for pHTN and MMDS1-associated complications in this population.

Phenotypic expansion of POGZ-related intellectual disability syndrome (White-Sutton syndrome).

White-Sutton syndrome (WHSUS) is a recently-identified genetic disorder resulting from de novo heterozygous pathogenic variants in POGZ. Thus far, over 50 individuals have been reported worldwide, however phenotypic characterization and data regarding the natural history are still incomplete. Here we report the clinical features of 22 individuals with 21 unique loss of function POGZ variants. We observed a broad spectrum of intellectual disability and/or developmental delay with or without autism, and speech delay in all individuals. Other common problems included ocular abnormalities, hearing loss and gait abnormalities. A validated sleep disordered breathing questionnaire identified symptoms of obstructive sleep apnea in 4/12 (33%) individuals. A higher-than-expected proportion of cases also had gastrointestinal phenotypes, both functional and anatomical, as well as genitourinary anomalies. In line with previous publications, we observed an increased body mass index (BMI) z-score compared to the general population (mean 0.59, median 0.9; p 0.0253). Common facial features included microcephaly, broad forehead, midface hypoplasia, triangular mouth, broad nasal root and flat nasal bridge. Analysis of the Baylor Genetics clinical laboratory database revealed that POGZ variants were implicated in approximately 0.14% of cases who underwent clinical exome sequencing for neurological indications with or without involvement of other body systems. This study describes a greater allelic series and expands the phenotypic spectrum of this new syndromic form of intellectual disability and autism.

GARS-related disease in infantile spinal muscular atrophy: Implications for diagnosis and treatment.

The majority of patients with spinal muscular atrophy (SMA) identified to date harbor a biallelic exonic deletion of SMN1. However, there have been reports of SMA-like disorders that are independent of SMN1, including those due to pathogenic variants in the glycyl-tRNA synthetase gene (GARS1). We report three unrelated patients with de novo variants in GARS1 that are associated with infantile-onset SMA (iSMA). Patients were ascertained during inpatient hospital evaluations for complications of neuropathy. Evaluations were completed as indicated for clinical care and management and informed consent for publication was obtained. One newly identified, disease-associated GARS1 variant, identified in two out of three patients, was analyzed by functional studies in yeast complementation assays. Genomic analyses by exome and/or gene panel and SMN1 copy number analysis of three patients identified two previously undescribed de novo missense variants in GARS1 and excluded SMN1 as the causative gene. Functional studies in yeast revealed that one of the de novo GARS1 variants results in a loss-of-function effect, consistent with other pathogenic GARS1 alleles. In sum, the patients' clinical presentation, assessments of previously identified GARS1 variants and functional assays in yeast suggest that the GARS1 variants described here cause iSMA. GARS1 variants have been previously associated with Charcot-Marie-Tooth disease (CMT2D) and distal SMA type V (dSMAV). Our findings expand the allelic heterogeneity of GARS-associated disease and support that severe early-onset SMA can be caused by variants in this gene. Distinguishing the SMA phenotype caused by SMN1 variants from that due to pathogenic variants in other genes such as GARS1 significantly alters approaches to treatment.

Case report and novel treatment of an autosomal recessive Leigh syndrome caused by short-chain enoyl-CoA hydratase deficiency.

Short chain enoyl-CoA hydratase (SCEH) deficiency leads to a severe form of autosomal recessive Leigh syndrome with inevitable neurological decline and early mortality. SCEH is most notably involved in valine catabolism, a deficiency of which results in various metabolic alterations, including increased levels of the highly reactive metabolite 2-methacrylyl-CoA. With no proven treatments available to date, it has been speculated that patients may respond to a valine restricted diet and/or N-acetylcysteine supplementation, as suggested by early studies of a very similar inborn error of metabolism, 3-hydroxyisobutyryl-CoA hydrolase deficiency. We describe a patient with typical Leigh syndrome clinical findings and identified compound heterozygous variants in ECSH1. Valine-restricted diet was initiated at 6 months of age and N-acetylcysteine supplementation at 9 months with subsequent improvement in growth and slow progress in developmental milestones. However, at 15 months, the patient aspirated during a breakthrough seizure from which he did not recover and died soon after from related complications. This report highlights some of the challenges that remain in the management and treatment of SCEH deficiency, while demonstrating that a valine restricted diet and N-acetylcysteine can be safely administered with the potential for clinical improvement.

Review of the phenotypic spectrum associated with haploinsufficiency of MYRF.

The myelin regulatory factor gene (MYRF) encodes a transcription factor that is widely expressed. There is increasing evidence that heterozygous loss-of-function variants in MYRF can lead to abnormal development of the heart, genitourinary tract, diaphragm, and lungs. Here, we searched a clinical database containing the results of 12,000 exome sequencing studies. We identified three previously unreported males with putatively deleterious variants in MYRF: one with a point mutation predicted to affect splicing and two with frameshift variants. In all cases where parental DNA was available, these variants were found to have arisen de novo. The phenotypes identified in these subjects included a variety of congenital heart defects (CHD) (hypoplastic left heart syndrome, scimitar syndrome, septal defects, and valvular anomalies), genitourinary anomalies (ambiguous genitalia, hypospadias, and cryptorchidism), congenital diaphragmatic hernia, and pulmonary hypoplasia. The phenotypes seen in our subjects overlap those described in individuals diagnosed with PAGOD syndrome [MIM# 202660], a clinically defined syndrome characterized by pulmonary artery and lung hypoplasia, agonadism, omphalocele, and diaphragmatic defects that can also be associated with hypoplastic left heart and scimitar syndrome. These cases provide additional evidence that haploinsufficiency of MYRF causes a genetic syndrome whose cardinal features include CHD, urogenital anomalies, congenital diaphragmatic hernia, and pulmonary hypoplasia. We also conclude that consideration should be given to screening individuals with PAGOD for pathogenic variants in MYRF, and that individuals with MYRF deficiency who survive the neonatal period should be monitored closely for developmental delay and intellectual disability.