We aimed to assess the definition of actionability of secondary findings in childhood, using a screening framework.
For 31 disorders on the American College of Medical Genetics and Genomics SF v.2.0 ...list, World Health Organization screening criteria were applied to assess actionability in childhood.
The age of onset was variable. We categorized disorders based on the proportion of cases that presented in childhood: rare (n = 6), fewer than half the cases (n = 9), the majority of cases (n = 12), or unclear (n = 4). The age at initiation of intervention was based on the youngest age of onset reported, not evidence of the benefit of early intervention. For 15 disorders, guidelines were supported by a moderate quality of evidence for at least one recommendation. Only tuberous sclerosis complex had recommendations based on high-quality evidence. All others were based on evidence of low or very low quality.
We propose that actionability in childhood should be based on the proportion of cases that manifest in childhood and the quality of the evidence supporting intervention recommendations. Ideally, disclosure in childhood would be limited to disorders for which a majority of cases present in childhood and for which interventions are supported by evidence of at least moderate quality (i.e., multiple endocrine neoplasia type 2, retinoblastoma, tuberous sclerosis complex, Marfan syndrome, and Wilson's disease).
The aim of this Position Statement is to provide recommendations for Canadian medical geneticists, clinical laboratory geneticists, genetic counsellors and other physicians regarding the use of ...genome-wide sequencing of germline DNA in the context of clinical genetic diagnosis. This statement has been developed to facilitate the clinical translation and development of best practices for clinical genome-wide sequencing for genetic diagnosis of monogenic diseases in Canada; it does not address the clinical application of this technology in other fields such as molecular investigation of cancer or for population screening of healthy individuals.
Two multidisciplinary groups consisting of medical geneticists, clinical laboratory geneticists, genetic counsellors, ethicists, lawyers and genetic researchers were assembled to review existing literature and guidelines on genome-wide sequencing for clinical genetic diagnosis in the context of monogenic diseases, and to make recommendations relevant to the Canadian context. The statement was circulated for comment to the Canadian College of Medical Geneticists (CCMG) membership-at-large and, following incorporation of feedback, approved by the CCMG Board of Directors. The CCMG is a Canadian organisation responsible for certifying medical geneticists and clinical laboratory geneticists, and for establishing professional and ethical standards for clinical genetics services in Canada.
Recommendations include (1) clinical genome-wide sequencing is an appropriate approach in the diagnostic assessment of a patient for whom there is suspicion of a significant monogenic disease that is associated with a high degree of genetic heterogeneity, or where specific genetic tests have failed to provide a diagnosis; (2) until the benefits of reporting incidental findings are established, we do not endorse the intentional clinical analysis of disease-associated genes other than those linked to the primary indication; and (3) clinicians should provide genetic counselling and obtain informed consent prior to undertaking clinical genome-wide sequencing. Counselling should include discussion of the limitations of testing, likelihood and implications of diagnosis and incidental findings, and the potential need for further analysis to facilitate clinical interpretation, including studies performed in a research setting. These recommendations will be routinely re-evaluated as knowledge of diagnostic and clinical utility of clinical genome-wide sequencing improves. While the document was developed to direct practice in Canada, the applicability of the statement is broader and will be of interest to clinicians and health jurisdictions internationally.
Thoracic aortic aneurysm and dissection (TAAD) is typically inherited in an autosomal dominant manner, but rare X-linked families have been described. So far, the only known X-linked gene is FLNA, ...which is associated with the periventricular nodular heterotopia type of Ehlers-Danlos syndrome. However, mutations in this gene explain only a small number of X-linked TAAD families.
We performed targeted resequencing of 368 candidate genes in a cohort of 11 molecularly unexplained Marfan probands. Subsequently, Sanger sequencing of BGN in 360 male and 155 female molecularly unexplained TAAD probands was performed.
We found five individuals with loss-of-function mutations in BGN encoding the small leucine-rich proteoglycan biglycan. The clinical phenotype is characterized by early-onset aortic aneurysm and dissection. Other recurrent findings include hypertelorism, pectus deformity, joint hypermobility, contractures, and mild skeletal dysplasia. Fluorescent staining revealed an increase in TGF-β signaling, evidenced by an increase in nuclear pSMAD2 in the aortic wall. Our results are in line with those of prior reports demonstrating that Bgn-deficient male BALB/cA mice die from aortic rupture.
In conclusion, BGN gene defects in humans cause an X-linked syndromic form of severe TAAD that is associated with preservation of elastic fibers and increased TGF-β signaling.
Genet Med19 4, 386–395.
Smooth muscle dysfunction syndrome (SMDS) due to heterozygous ACTA2 arginine 179 alterations is characterized by patent ductus arteriosus, vasculopathy (aneurysm and occlusive lesions), pulmonary ...arterial hypertension, and other complications in smooth muscle-dependent organs. We sought to define the clinical history of SMDS to develop recommendations for evaluation and management.
Medical records of 33 patients with SMDS (median age 12 years) were abstracted and analyzed.
All patients had congenital mydriasis and related pupillary abnormalities at birth and presented in infancy with a patent ductus arteriosus or aortopulmonary window. Patients had cerebrovascular disease characterized by small vessel disease (hyperintense periventricular white matter lesions; 95%), intracranial artery stenosis (77%), ischemic strokes (27%), and seizures (18%). Twelve (36%) patients had thoracic aortic aneurysm repair or dissection at median age of 14 years and aortic disease was fully penetrant by the age of 25 years. Three (9%) patients had axillary artery aneurysms complicated by thromboembolic episodes. Nine patients died between the ages of 0.5 and 32 years due to aortic, pulmonary, or stroke complications, or unknown causes.
Based on these data, recommendations are provided for the surveillance and management of SMDS to help prevent early-onset life-threatening complications.
Loeys-Dietz Syndrome (LDS) is an autosomal dominant connective tissue disorder. The major hallmark of LDS is thoracic aortic aneurysm and dissection (TAAD). We generated an induced pluripotent stem ...cell (iPSC) line of a severely affected LDS patient carrying a pathogenic SMAD3 p.Arg287Gln variant. Peripheral blood mononuclear cells were reprogrammed using non-integrating Sendai viral vectors. The autonomous pluripotency state of the resulting iPSC model was proven by the presence of pluripotency markers, trilineage differentiation potential and absence of the Sendai vector backbone. This iPSC line can be used to study and/or therapeutically target the cellular pathomechanisms of SMAD3-related LDS.
We investigated seven children from six families to expand the phenotypic spectrum associated with an early infantile epileptic encephalopathy caused by biallelic pathogenic variants in the ...phosphatidylinositol glycan anchor biosynthesis class Q (PIGQ) gene. The affected children were all identified by clinical or research exome sequencing. Clinical data, including EEGs and MRIs, was comprehensively reviewed and flow cytometry and transfection experiments were performed to investigate PIGQ function. Pathogenic biallelic PIGQ variants were associated with increased mortality. Epileptic seizures, axial hypotonia, developmental delay and multiple congenital anomalies were consistently observed. Seizure onset occurred between 2.5 months and 7 months of age and varied from treatable seizures to recurrent episodes of status epilepticus. Gastrointestinal issues were common and severe, two affected individuals had midgut volvulus requiring surgical correction. Cardiac anomalies including arrythmias were observed. Flow cytometry using granulocytes and fibroblasts from affected individuals showed reduced expression of glycosylphosphatidylinositol (GPI)‐anchored proteins. Transfection of wildtype PIGQ cDNA into patient fibroblasts rescued this phenotype. We expand the phenotypic spectrum of PIGQ‐related disease and provide the first functional evidence in human cells of defective GPI‐anchoring due to pathogenic variants in PIGQ.
Intronic variants outside the canonical splice site are challenging to interpret and therefore likely represent an underreported cause of human disease. Autosomal recessive variants in DYNC2H1 are ...associated with short-rib thoracic dysplasia 3 with or without polydactyly (SRTD3), a clinically heterogeneous disease generally presenting with short ribs, shortened tubular bones, narrow thorax and acetabular roof anomalies. We describe a case of SRTD3 with compound heterozygous frameshift and intronic variants and highlight the essential role of RNA sequencing (RNA-Seq) in variant interpretation.
Following inconclusive clinical genetic testing identifying a likely pathogenic frameshift variant and an intronic variant of uncertain significance (VUS) in DYNC2H1 in trans, the family enrolled in the Care4Rare Canada research program, where RNA-Seq studies were performed.
The proband presented with post-axial polydactyly of all four limbs, a significantly small chest with a pectus excavatum and anterior flaring of the ribs. RNA-Seq investigations revealed a novel splice junction as a result of the intronic VUS and significantly decreased DYNC2H1 gene expression in the proband.
This case demonstrates the diagnostic utility of RNA-Seq for variant interpretation following inconclusive clinical testing, which can ultimately lead to diagnosis for patients with rare disease.
Abstract The knowledge surrounding the genetic etiologies of familial aortopathies and familial thoracic aortic aneurysms and dissections has greatly expanded over the past few years. However, ...despite these advances, the underlying molecular etiology remains unidentified in most families with nonsyndromic familial aortopathies, and in a subset of families with syndromic aortopathies. In these families we cannot offer a genetic test to establish which family members are at risk. Although the general consensus has been to clinically follow all at-risk family members on the basis of family history, it remains unclear at the age at which to initiate clinical surveillance and the frequency which to screen asymptomatic relatives, whether or not a genetic etiology has been established in the family. These questions are particularly troublesome in a pediatric context where the risks of screening are potentially higher and the likelihood that such screening will provide immediate benefits is often lower than in adults. In this report we aim to: (1) provide clinicians with a framework within which to evaluate risks and benefits of screening asymptomatic pediatric patients for a family history of thoracic aortic aneurysms and dissections; and (2) provide a potential approach for patients (a) in whose family a disease-causing mutation has been identified, (b) patients in whose family the proband is syndromic, but does not have an identified disease-causing mutation, and (c) patients in whose family the proband is nonsyndromic and does not have an identified disease-causing mutation.
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