Phenotypic heterogeneity associated with KIF21A: Two new cases and review of the literature.

Our understanding of genetic and phenotypic heterogeneity associated with the clinical spectrum of rare diseases continues to expand. Thorough phenotypic descriptions and model organism functional studies are valuable tools in dissecting the biology of the disease process. Kinesin genes are well known to be associated with specific disease phenotypes and a subset of kinesin genes, including KIF21A, have been associated with more than one disease. Here we report two patients with KIF21A variants identified by exome sequencing; one with biallelic variants, supporting a novel KIF21A related syndrome with recessive inheritance and the second report of this condition, and another with a heterozygous de novo variant allele representing a phenotypic expansion of the condition described to date. We provide detailed phenotypic information on both families, including a novel neuropathology finding of neuroaxonal dystrophy associated with biallelic variants in KIF21A. Additionally, we studied the dominant variant in Saccharomyces cerevisiae to assess variant pathogenicity and found that this variant appears to impair protein function. KIF21A associated disease has mounting evidence for phenotypic heterogeneity; further patients and study of an allelic series are required to define the phenotypic spectrum and further explore the molecular etiology for each of these conditions.

Evaluation of the diagnostic accuracy of exome sequencing and its impact on diagnostic thinking for patients with rare disease in a publicly funded health care system: A prospective cohort study.

PURPOSE: To evaluate the diagnostic utility of publicly funded clinical exome sequencing (ES) for patients with suspected rare genetic diseases. METHODS: We prospectively enrolled 297 probands who met eligibility criteria and received ES across 5 sites in Ontario, Canada, and extracted data from medical records and clinician surveys. Using the Fryback and Thornbury Efficacy Framework, we assessed diagnostic accuracy by examining laboratory interpretation of results and assessed diagnostic thinking by examining the clinical interpretation of results and whether clinical-molecular diagnoses would have been achieved via alternative hypothetical molecular tests. RESULTS: Laboratories reported 105 molecular diagnoses and 165 uncertain results in known and novel genes. Of these, clinicians interpreted 102 of 105 (97%) molecular diagnoses and 6 of 165 (4%) uncertain results as clinical-molecular diagnoses. The 108 clinical-molecular diagnoses were in 104 families (35% diagnostic yield). Each eligibility criteria resulted in diagnostic yields of 30% to 40%, and higher yields were achieved when >2 eligibility criteria were met (up to 45%). Hypothetical tests would have identified 61% of clinical-molecular diagnoses. CONCLUSION: We demonstrate robustness in eligibility criteria and high clinical validity of laboratory results from ES testing. The importance of ES was highlighted by the potential 40% of patients that would have gone undiagnosed without this test.

Elucidating the clinical and molecular spectrum of SMARCC2-associated NDD in a cohort of 65 affected individuals.

PURPOSE: Coffin-Siris and Nicolaides-Baraitser syndromes are recognizable neurodevelopmental disorders caused by germline variants in BAF complex subunits. The SMARCC2 BAFopathy was recently reported. Herein, we present clinical and molecular data on a large cohort. METHODS: Clinical symptoms for 41 novel and 24 previously published affected individuals were analyzed using the Human Phenotype Ontology. For genotype-phenotype correlations, molecular data were standardized and grouped into non-truncating and likely gene-disrupting (LGD) variants. Missense variant protein expression and BAF-subunit interactions were examined using 3D protein modeling, co-immunoprecipitation, and proximity-ligation assays. RESULTS: Neurodevelopmental delay with intellectual disability, muscular hypotonia, and behavioral disorders were the major manifestations. Clinical hallmarks of BAFopathies were rare. Clinical presentation differed significantly, with LGD variants being predominantly inherited and associated with mildly reduced or normal cognitive development, whereas non-truncating variants were mostly de novo and presented with severe developmental delay. These distinct manifestations and non-truncating variant clustering in functional domains suggest different pathomechanisms. In vitro testing showed decreased protein expression for N-terminal missense variants similar to LGD. CONCLUSION: This study improved SMARCC2 variant classification and identified discernible SMARCC2-associated phenotypes for LGD and non-truncating variants, which were distinct from other BAFopathies. The pathomechanism of most non-truncating variants has yet to be investigated.

Homozygous WNT9B variants in two families with bilateral renal agenesis/hypoplasia/dysplasia.

WNT9B plays a key role in the development of the mammalian urogenital system. It is essential for the induction of mesonephric and metanephric tubules, the regulation of renal tubule morphogenesis, and the regulation of renal progenitor cell expansion and differentiation. To our knowledge, WNT9B has not been associated with renal defects in humans; however, WNT9B-/- mice have renal agenesis/hypoplasia and reproductive tract abnormalities. We report four individuals from two unrelated consanguineous families with bilateral renal agenesis/hypoplasia/dysplasia and homozygous variants in WNT9B. The proband from Family 1 has bilateral renal cystic dysplasia and chronic kidney disease. He has two deceased siblings who presented with bilateral renal hypoplasia/agenesis. The three affected family members were homozygous for a missense variant in WNT9B (NM_003396.2: c.949G>A/p.(Gly317Arg)). The proband from Family 2 has renal hypoplasia/dysplasia, chronic kidney disease, and is homozygous for a nonsense variant in WNT9B (NM_003396.2: c.11dupC/p.(Pro5Alafs*52)). Two of her siblings died in the neonatal period, one confirmed to be in the context of oligohydramnios. The proband's unaffected brother is also homozygous for the nonsense variant in WNT9B, suggesting nonpenetrance. We propose a novel association of WNT9B and renal anomalies in humans. Further study is needed to delineate the contribution of WNT9B to genitourinary anomalies in humans.

A pilot eConsultation service in Eastern Ontario: bridging clinical genetics and primary care.

With the rising demand for clinical genetics services, it is a challenge for clinical geneticists to meet the needs of patients and referring primary care providers in a timely way, using current models of genetics health care delivery. One method of providing primary care providers with greater access to clinical genetics expertise is through an electronic consultation (eConsult) service. We describe here a pilot project of a clinical genetics eConsult service that our genetics centre in Eastern Ontario, Canada provided, using the Champlain Building Access to Specialists through eConsultation (BASE)TM web-based application. We analyzed 111 genetics eConsults submitted by primary care providers to a single clinical geneticist over a 28-month time period. More than half (54%) of the eConsult questions were regarding (1) hereditary cancer and (2) genetic syndromes, with the remainder encompassing a wide variety of clinical genetics topics. We avoided a referral to the Genetics clinic for an in-person appointment for 30% of the eConsult cases, based on a contemplated referral rate to Genetics clinic of 72% prior to eConsult and a planned referral rate to Genetics clinic of 42% following all eConsults. Primary care providers rated the eConsult service of high value to themselves and also to their patients. This pilot service supports the potential of an eConsultation service to create a stronger and more dynamic link between clinical genetics and primary care providers, which may lead to better patient care.

A retrospective review of 48 individuals, including 12 families, molecularly diagnosed with hereditary leiomyomatosis and renal cell cancer (HLRCC).

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is caused by autosomal dominant germline mutations in the fumarate hydratase (FH) gene and is characterized by cutaneous leiomyomas, uterine leiomyomas and aggressive renal malignancies. We conducted a retrospective chart review to characterize the patients referred to our Regional Genetics Program for assessment of HLRCC from 2004 to mid-2016. Forty-eight of 69 (69.5%) referred individuals were positive for a pathogenic or likely pathogenic variant in FH; they had an average age of 39.1 years. There were 11 different FH variants among them. As expected, the most sensitive indications for a positive genetic test were papillary renal cell carcinoma (RCC) at a young age (5/5; 100%) and multiple cutaneous leiomyomas (18/19; 95%). However, only twenty-two of 48 (46%) individuals with a positive molecular test had cutaneous leiomyomas, which is considerably lower than previously reported and supports the likelihood of ascertainment bias in previous reports. Notably, we have experience with 1 large family in which there were no cutaneous leiomyomas across a large age range. We confirm that multiple cutaneous leiomyomas and papillary RCCs at a young age have a high positive predictive value for a molecular diagnosis of HLRCC, but that cutaneous leiomyomas are less prevalent in HLRCC than previously understood, and therefore the condition is likely to be under-ascertained. Our understanding of the phenotypic spectrum of HLRCC is still evolving.

Autosomal dominant cutis laxa with progeroid features due to a novel, de novo mutation in ALDH18A1.

De novo dominant mutations in the aldehyde dehydrogenase 18 family member A1 (ALDH18A1) gene have recently been shown to cause autosomal dominant cutis laxa with progeroid features (MIM 616603). To date, all de novo dominant mutations have been found in a single highly conserved amino acid residue at position p.Arg138. We report an 8-year-old male with a clinical diagnosis of autosomal dominant cutis laxa (ADCL) with progeroid features and a novel de novo missense mutation in ALDH18A1 (NM_002860.3: c.377G>A (p.Arg126His)). This is the first report of an individual with ALDH18A1-ADCL due to a substitution at a residue other than p.Arg138. Knowledge of the complete spectrum of dominant-acting mutations that cause this rare syndrome will have implications for molecular diagnosis and genetic counselling of these families.