The 8th International RASopathies Symposium: Expanding research and care practice through global collaboration and advocacy

Germline pathogenic variants in the RAS/mitogen-activated protein kinase (MAPK) signaling pathway are the molecular cause of RASopathies, a group of clinically overlapping genetic syndromes. RASopathies constitute a wide clinical spectrum characterized by distinct facial features, short stature, predisposition to cancer, and variable anomalies in nearly all the major body systems. With increasing global recognition of these conditions, the 8th International RASopathies Symposium spotlighted global perspectives on clinical care and research, including strategies for building international collaborations and developing diverse patient cohorts in anticipation of interventional trials. This biannual meeting, organized by RASopathies Network, was held in a hybrid virtual/in-person format. The agenda featured emerging discoveries and case findings as well as progress in preclinical and therapeutic pipelines. Stakeholders including basic scientists, clinician-scientists, practitioners, industry representatives, patients, and family advocates gathered to discuss cutting edge science, recognize current gaps in knowledge, and hear from people with RASopathies about the experience of daily living. Presentations by RASopathy self-advocates and early-stage investigators were featured throughout the program to encourage a sustainable, diverse, long-term research and advocacy partnership focused on improving health and bringing treatments to people with RASopathies.

Supporting Parents Throughout the Genetic Testing Process and New Diagnosis

Receiving a genetic diagnosis can be challenging for parents as they learn to cope and adapt to this news. They often experience a myriad of emotions ranging from shock to relief. Yet overwhelmingly, parents report a negative experience with this process. Factors that improve parental satisfaction include being provided written information, emotional and psychosocial support, and connections with other parents. Genetics care providers are particularly equipped to solicit parental needs and provide support before, during, and after receiving a diagnosis. This review will provide suggestions and recommendations for supporting parents throughout the diagnostic testing experience and receiving a genetic diagnosis.

The cascade screening in heritable forms of pulmonary arterial hypertension

Heritable pulmonary artery hypertension (HPAH) is an increasingly recognized type of pulmonary arterial hypertension, in both pediatric and adult population. Intrinsic to hereditary disease, screening for genetic mutations within families is an important component of diagnosis and understanding burden of disease. Recently, consensus guidelines are published for genetic screening in PAH. These guidelines include recommendations for screening at diagnosis, noting individuals with presumed PAH due to familial, or idiopathic etiologies. Cascade genetic testing is specifically recommended as a testing paradigm to screen relatives for detection of mutation carriers, who may be asymptomatic. Without targeted genetic testing, familial mutation carriers may only come to attention when pulmonary vascular disease burden is high enough to cause symptoms, suggesting more advanced disease. Here, we present our collective experience with HPAH in five distinct families, specifically to report on the clinical courses of patients who were diagnosed with genetic mutation at diagnosis versus those who were offered genetic screening. In three families, asymptomatic mutation carriers were identified and monitored for clinical worsening. In two families, screening was not done and affected family members presented with advanced disease.

Barriers to a successful healthcare transition for individuals with urea cycle disorders

The pediatric to adult healthcare transition (HCT) is a process for individuals with chronic health conditions to gradually shift from a pediatric to an adult-oriented care system. Autonomy and self-management skills required for an individual's HCT readiness can be evaluated through the transition readiness assessment questionnaire (TRAQ). Despite general HCT preparation guidelines, little is known about the HCT experience of individuals with a urea cycle disorder (UCD). This is the first study to report the parent or guardian perception of the HCT process in children with a UCD by investigating the stages of transition readiness and transition outcome. We identify barriers to HCT readiness and planning, along with deficiencies in transition outcome for individuals with a UCD. For children that received special education services compared to those that did not, significantly lower transition readiness scores were identified in the total TRAQ score (p = 0.03) and in the domains of tracking health issues (p = 0.02), talking with providers (p = 0.03), and managing daily activities (p = 0.01). There was a lack of HCT preparation as most subjects did not have a HCT discussion with their healthcare provider before age 26. Deficiencies in HCT outcome are demonstrated by individuals with a UCD reporting delays in needed medical care and dissatisfaction with their healthcare services. Considerations for facilitating a successful HCT for individuals with a UCD include providing individualized education, appointing a transition coordinator, allowing flexibility in HCT timing, and ensuring that the individual recognizes concerning UCD symptoms and knows when to seek medical care.

The seventh international RASopathies symposium: Pathways to a cure-expanding knowledge, enhancing research, and therapeutic discovery

RASopathies are a group of genetic disorders that are caused by genes that affect the canonical Ras/mitogen-activated protein kinase (MAPK) signaling pathway. Despite tremendous progress in understanding the molecular consequences of these genetic anomalies, little movement has been made in translating these findings to the clinic. This year, the seventh International RASopathies Symposium focused on expanding the research knowledge that we have gained over the years to enhance new discoveries in the field, ones that we hope can lead to effective therapeutic treatments. Indeed, for the first time, research efforts are finally being translated to the clinic, with compassionate use of Ras/MAPK pathway inhibitors for the treatment of RASopathies. This biannual meeting, organized by the RASopathies Network, brought together basic scientists, clinicians, clinician scientists, patients, advocates, and their families, as well as representatives from pharmaceutical companies and the National Institutes of Health. A history of RASopathy gene discovery, identification of new disease genes, and the latest research, both at the bench and in the clinic, were discussed.

Evaluation and classification of severity for 176 genes on an expanded carrier screening panel

Background

Disease severity is important when considering genes for inclusion on reproductive expanded carrier screening (ECS) panels. We applied a validated and previously published algorithm that classifies diseases into four severity categories (mild, moderate, severe, and profound) to 176 genes screened by ECS. Disease traits defining severity categories in the algorithm were then mapped to four severity‐related ECS panel design criteria cited by the American College of Obstetricians and Gynecologists (ACOG).

Methods

Eight genetic counselors (GCs) and four medical geneticists (MDs) applied the severity algorithm to subsets of 176 genes. MDs and GCs then determined by group consensus how each of these disease traits mapped to ACOG severity criteria, enabling determination of the number of ACOG severity criteria met by each gene.

Results

Upon consensus GC and MD application of the severity algorithm, 68 (39%) genes were classified as profound, 71 (40%) as severe, 36 (20%) as moderate, and one (1%) as mild. After mapping of disease traits to ACOG severity criteria, 170 out of 176 genes (96.6%) were found to meet at least one of the four criteria, 129 genes (73.3%) met at least two, 73 genes (41.5%) met at least three, and 17 genes (9.7%) met all four.

Conclusion

This study classified the severity of a large set of Mendelian genes by collaborative clinical expert application of a trait‐based algorithm. Further, it operationalized difficult to interpret ACOG severity criteria via mapping of disease traits, thereby promoting consistency of ACOG criteria interpretation.

Loss-of-function mutations in Lysyl-tRNA synthetase cause various leukoencephalopathy phenotypes

OBJECTIVE

To expand the clinical spectrum of lysyl-tRNA synthetase (KARS) gene-related diseases, which so far includes Charcot-Marie-Tooth disease, congenital visual impairment and microcephaly, and nonsyndromic hearing impairment.

METHODS

Whole-exome sequencing was performed on index patients from 4 unrelated families with leukoencephalopathy. Candidate pathogenic variants and their cosegregation were confirmed by Sanger sequencing. Effects of mutations on KARS protein function were examined by aminoacylation assays and yeast complementation assays.

RESULTS

Common clinical features of the patients in this study included impaired cognitive ability, seizure, hypotonia, ataxia, and abnormal brain imaging, suggesting that the CNS involvement is the main clinical presentation. Six previously unreported and 1 known KARS mutations were identified and cosegregated in these families. Two patients are compound heterozygous for missense mutations, 1 patient is homozygous for a missense mutation, and 1 patient harbored an insertion mutation and a missense mutation. Functional and structural analyses revealed that these mutations impair aminoacylation activity of lysyl-tRNA synthetase, indicating that defective KARS function is responsible for the phenotypes in these individuals.

CONCLUSIONS

Our results demonstrate that patients with loss-of-function KARS mutations can manifest CNS disorders, thus broadening the phenotypic spectrum associated with KARS-related disease.

Biallelic mutations in the ferredoxin reductase gene cause novel mitochondriopathy with optic atrophy

Iron-sulfur (Fe-S) clusters are ubiquitous cofactors essential to various cellular processes, including mitochondrial respiration, DNA repair, and iron homeostasis. A steadily increasing number of disorders are being associated with disrupted biogenesis of Fe-S clusters. Here, we conducted whole-exome sequencing of patients with optic atrophy and other neurological signs of mitochondriopathy and identified 17 individuals from 13 unrelated families with recessive mutations in FDXR, encoding the mitochondrial membrane-associated flavoprotein ferrodoxin reductase required for electron transport from NADPH to cytochrome P450. In vitro enzymatic assays in patient fibroblast cells showed deficient ferredoxin NADP reductase activity and mitochondrial dysfunction evidenced by low oxygen consumption rates (OCRs), complex activities, ATP production and increased reactive oxygen species (ROS). Such defects were rescued by overexpression of wild-type FDXR. Moreover, we found that mice carrying a spontaneous mutation allelic to the most common mutation found in patients displayed progressive gait abnormalities and vision loss, in addition to biochemical defects consistent with the major clinical features of the disease. Taken together, these data provide the first demonstration that germline, hypomorphic mutations in FDXR cause a novel mitochondriopathy and optic atrophy in humans.

Genetic counselors on the frontline of precision health

By enabling precise genetic diagnosis and treatment there is great potential for inexpensive, accurate, and widely accessible genomic information to transform health care and improve the general well-being of virtually every person. To maximize this potential, approaches to genetic counseling and the role of genetic counselors will need to adapt to fit changing clinical and commercial needs worldwide. This will require overcoming multiple challenges including an inadequate workforce; development and implementation of alternate models of service delivery; integration of new technologies to improve, extend, and expand services; and support for equitable education and counseling among all populations. Genetic counselors are aptly poised to take on these challenges. The result will be better informed patients and families more capable of utilizing genetic information appropriately, making autonomous decisions about their care, and modifying their approach to disease risk to actively contribute to their health. The contributors to this issue of Seminars discuss how key areas of genetic counseling need to evolve and how genetic counselors can play a role in shaping the future of precision health.

Clinical Metabolomics to Segregate Aromatic Amino Acid Decarboxylase Deficiency From Drug-Induced Metabolite Elevations

BACKGROUND

Phenotyping technologies featured in the diagnosis of inborn errors of metabolism, such as organic acid, amino acid, and acylcarnitine analyses, recently have been supplemented by broad-scale untargeted metabolomic phenotyping. We investigated the analyte changes associated with aromatic amino acid decarboxylase (AADC) deficiency and dopamine medication treatment.

METHODS

Using an untargeted metabolomics platform, we analyzed ethylenediaminetetraacetic acid plasma specimens, and biomarkers were identified by comparing the biochemical profile of individual patient samples to a pediatric-centric population cohort.

RESULTS

Elevated 3-methoxytyrosine (average z score 5.88) accompanied by significant decreases of dopamine 3-O-sulfate (-2.77), vanillylmandelate (-2.87), and 3-methoxytyramine sulfate (-1.44) were associated with AADC deficiency in three samples from two patients. In five non-AADC patients treated with carbidopa-levodopa, levels of 3-methoxytyrosine were elevated (7.65); however, the samples from non-AADC patients treated with DOPA-elevating drugs had normal or elevated levels of metabolites downstream of aromatic l-amino acid decarboxylase, including dopamine 3-O-sulfate (2.92), vanillylmandelate (0.33), and 3-methoxytyramine sulfate (5.07). In one example, a plasma metabolomic phenotype pointed to a probable AADC deficiency and prompted the evaluation of whole exome sequencing data, identifying homozygosity for a known pathogenic variant, whereas whole exome analysis in a second patient revealed compound heterozygosity for two variants of unknown significance.

CONCLUSIONS

These data demonstrate the power of combining broad-scale genotyping and phenotyping technologies to diagnose inherited neurometabolic disorders and suggest that metabolic phenotyping of plasma can be used to identify AADC deficiency and to distinguish it from non-AADC patients with elevated 3-methoxytyrosine caused by DOPA-raising medications.

Cardio-facio-cutaneous syndrome: clinical features, diagnosis, and management guidelines

Cardio-facio-cutaneous syndrome (CFC) is one of the RASopathies that bears many clinical features in common with the other syndromes in this group, most notably Noonan syndrome and Costello syndrome. CFC is genetically heterogeneous and caused by gene mutations in the Ras/mitogen-activated protein kinase pathway. The major features of CFC include characteristic craniofacial dysmorphology, congenital heart disease, dermatologic abnormalities, growth retardation, and intellectual disability. It is essential that this condition be differentiated from other RASopathies, as a correct diagnosis is important for appropriate medical management and determining recurrence risk. Children and adults with CFC require multidisciplinary care from specialists, and the need for comprehensive management has been apparent to families and health care professionals caring for affected individuals. To address this need, CFC International, a nonprofit family support organization that provides a forum for information, support, and facilitation of research in basic medical and social issues affecting individuals with CFC, organized a consensus conference. Experts in multiple medical specialties provided clinical management guidelines for pediatricians and other care providers. These guidelines will assist in an accurate diagnosis of individuals with CFC, provide best practice recommendations, and facilitate long-term medical care.

Deletion of MAP2K2/MEK2: a novel mechanism for a RASopathy?

RASopathies are a class of genetic syndromes caused by germline mutations in genes encoding Ras/mitogen-activated protein kinase (Ras/MAPK) pathway components. Cardio-facio-cutaneous (CFC) syndrome is a RASopathy characterized by distinctive craniofacial features, skin and hair abnormalities, and congenital heart defects caused by activating mutations of BRAF, MEK1, MEK2, and KRAS. We define the phenotype of seven patients with de novo deletions of chromosome 19p13.3 including MEK2; they present with a distinct phenotype but have overlapping features with CFC syndrome. Phenotypic features of all seven patients include tall forehead, thick nasal tip, underdeveloped cheekbones, long midface, sinuous upper vermilion border, tall chin, angular jaw, and facial asymmetry. Patients also have developmental delay, hypotonia, heart abnormalities, failure to thrive, obstructive sleep apnea, gastroesophageal reflux and integument abnormalities. Analysis of epidermal growth factor-stimulated fibroblasts revealed that P-MEK1/2 was ∼50% less abundant in cells carrying the MEK2 deletion compared to the control. Significant differences in total MEK2 and Sprouty1 abundance were also observed. Our cohort of seven individuals with MEK2 deletions has overlapping features associated with RASopathies. This is the first report suggesting that, in addition to activating mutations, MEK2 haploinsufficiency can lead to dysregulation of the MAPK pathway.

Systemic primary carnitine deficiency: an overview of clinical manifestations, diagnosis, and management

Systemic primary carnitine deficiency (CDSP) is an autosomal recessive disorder of carnitine transportation. The clinical manifestations of CDSP can vary widely with respect to age of onset, organ involvement, and severity of symptoms, but are typically characterized by episodes of hypoketotic hypoglycemia, hepatomegaly, elevated transaminases, and hyperammonemia in infants; skeletal myopathy, elevated creatine kinase (CK), and cardiomyopathy in childhood; or cardiomyopathy, arrhythmias, or fatigability in adulthood. The diagnosis can be suspected on newborn screening, but is established by demonstration of low plasma free carnitine concentration (<5 μM, normal 25-50 μM), reduced fibroblast carnitine transport (<10% of controls), and molecular testing of the SLC22A5 gene. The incidence of CDSP varies depending on ethnicity; however the frequency in the United States is estimated to be approximately 1 in 50,000 individuals based on newborn screening data. CDSP is caused by recessive mutations in the SLC22A5 gene. This gene encodes organic cation transporter type 2 (OCTN2) which transport carnitine across cell membranes. Over 100 mutations have been reported in this gene with the c.136C > T (p.P46S) mutation being the most frequent mutation identified. CDSP should be differentiated from secondary causes of carnitine deficiency such as various organic acidemias and fatty acid oxidation defects. CDSP is an autosomal recessive condition; therefore the recurrence risk in each pregnancy is 25%. Carrier screening for at-risk individuals and family members should be obtained by performing targeted mutation analysis of the SLC22A5 gene since plasma carnitine analysis is not a sufficient methodology for determining carrier status. Antenatal diagnosis for pregnancies at increased risk of CDSP is possible by molecular genetic testing of extracted DNA from chorionic villus sampling or amniocentesis if both mutations in SLC22A5 gene are known. Once the diagnosis of CDSP is established in an individual, an echocardiogram, electrocardiogram, CK concentration, liver transaminanses measurement, and pre-prandial blood sugar levels, should be performed for baseline assessment. Primary treatment involves supplementation of oral levocarnitine (L-carnitine) at a dose of 50-400 mg/kg/day divided into three doses. No formal surveillance guidelines for individuals with CDSP have been established to date, however the following screening recommendations are suggested: annual echocardiogram and electrocardiogram, frequent plasma carnitine levels, and CK and liver transaminases measurement can be considered during acute illness. Adult women with CDSP who are planning to or are pregnant should meet with a metabolic or genetic specialist ideally before conception to discuss management of carnitine levels during pregnancy since carnitine levels are typically lower during pregnancy. The prognosis for individuals with CDSP depends on the age, presentation, and severity of symptoms at the time of diagnosis; however the long-term prognosis is favorable as long as individuals remain on carnitine supplementation.

Exploring the utility of whole-exome sequencing as a diagnostic tool in a child with atypical episodic muscle weakness

The advent of whole-exome next-generation sequencing (WES) has been pivotal for the molecular characterization of Mendelian disease; however, the clinical applicability of WES has remained relatively unexplored. We describe our exploration of WES as a diagnostic tool in a 3½-year old female patient with a 2-year history of episodic muscle weakness and paroxysmal dystonia who presented following a previous extensive but unrevealing diagnostic work-up. WES was performed on the proband and her two parents. Parental exome data was used to filter potential de novo genomic events in the proband and suspected variants were confirmed using di-deoxy sequencing. WES revealed a de novo non-synonymous mutation in exon 21 of the calcium channel gene CACNA1S that has been previously reported in a single patient as a rare cause of atypical hypokalemic periodic paralysis. This was unexpected, as the proband's original differential diagnosis had included hypokalemic periodic paralysis, but clinical and laboratory features were equivocal, and standard clinical molecular testing for hypokalemic periodic paralysis and related disorders was negative. This report highlights the potential diagnostic utility of WES in clinical practice, with implications for the approach to similar diagnostic dilemmas in the future.

Chromosome 15q24 microdeletion syndrome

Chromosome 15q24 microdeletion syndrome is a recently described rare microdeletion syndrome that has been reported in 19 individuals. It is characterized by growth retardation, intellectual disability, and distinct facial features including long face with high anterior hairline, hypertelorism, epicanthal folds, downslanting palpebral fissures, sparse and broad medial eyebrows, broad and/or depressed nasal bridge, small mouth, long smooth philtrum, and full lower lip. Other common findings include skeletal and digital abnormalities, genital abnormalities in males, hypotonia, behavior problems, recurrent infections, and eye problems. Other less frequent findings include hearing loss, growth hormone deficiency, hernias, and obesity. Congenital malformations, while rare, can be severe and include structural brain anomalies, cardiovascular malformations, congenital diaphragmatic hernia, intestinal atresia, imperforate anus, and myelomeningocele. Karyotypes are typically normal, and the deletions were detected in these individuals by array comparative genomic hybridization (aCGH). The deletions range in size from 1.7-6.1 Mb and usually result from nonallelic homologous recombination (NAHR) between paralogous low-copy repeats (LCRs). The majority of 15q24 deletions have breakpoints that localize to one of five LCR clusters labeled LCR15q24A, -B, -C, -D, and -E. The smallest region of overlap (SRO) spans a 1.2 Mb region between LCR15q24B to LCR15q24C. There are several candidate genes within the SRO, including CYP11A1, SEMA7A, CPLX3, ARID3B, STRA6, SIN3A and CSK, that may predispose to many of the clinical features observed in individuals with 15q24 deletion syndrome. The deletion occurred as a de novo event in all of the individuals when parents were available for testing. Parental aCGH and/or FISH studies are recommended to provide accurate genetic counseling and guidance regarding prognosis, recurrence risk, and reproductive options. Management involves a multi-disciplinary approach to care with the primary care physician and clinical geneticist playing a crucial role in providing appropriate screening, surveillance, and care for individuals with this syndrome. At the time of diagnosis, individuals should receive baseline echocardiograms, audiologic, ophthalmologic, and developmental assessments. Growth and feeding should be closely monitored. Other specialists that may be involved in the care of individuals with 15q24 deletion syndrome include immunology, endocrine, orthopedics, neurology, and urology. Chromosome 15q24 microdeletion syndrome should be differentiated from other genetic syndromes, particularly velo-cardio-facial syndrome (22q11.2 deletion syndrome), Prader-Willi syndrome, and Noonan syndrome. These conditions share some phenotypic similarity to 15q24 deletion syndrome yet have characteristic features specific to each of them that allows the clinician to distinguish between them. Molecular genetic testing and/or aCGH will be able to diagnose these conditions in the majority of individuals.

Adults with genetic syndromes and cardiovascular abnormalities: clinical history and management

Cardiovascular abnormalities, especially structural congenital heart defects, commonly occur in malformation syndromes and genetic disorders. Individuals with syndromes comprise a significant proportion of those affected with selected congenital heart defects such as complete atrioventricular canal, interrupted arch type B, supravalvar aortic stenosis, and pulmonary stenosis. As these individuals age, they contribute to the growing population of adults with special health care needs. Although most will require longterm cardiology follow-up, primary care providers, geneticists, and other specialists should be aware of (1) the type and frequency of cardiovascular abnormalities, (2) the range of clinical outcomes, and (3) guidelines for prospective management and treatment of potential complications. This article reviews fundamental genetic, cardiac, medical, and reproductive issues associated with common genetic syndromes that are frequently associated with a cardiovascular abnormality. New data are also provided about the cardiac status of adults with a 22q11.2 deletion and with Down syndrome.