Variable Phenotypic Expression Research Articles

A novel frameshift TBX4 variant in a family with ischio-coxo-podo-patellar syndrome and variable severity.

Congenital anomalies of the knee are a spectrum of rare disorders with wide clinical and genetic variability, which are mainly due to the complex processes underlying knee development. Despite progresses in understanding pathomechanisms and associated genes, many patients remain undiagnosed. To uncover the genetic bases of a congenital patellar dislocation affecting multiple family members with variable severity. We performed ES in the proband and his father, both showing bilateral patellar dislocation, his sister with a milder similar condition, and his unaffected mother. Sanger sequencing was then performed in the proband's brother and paternal aunt, both affected as well. ES and Sanger sequencing identified the presence of the novel heterozygous frameshift mutation c.735delT in the TBX4 gene in all affected family members. TBX4 is associated with autosomal dominant ischio-coxo-podo-patellar syndrome with/without pulmonary arterial hypertension (ICPPS, #147891), reaching a diagnosis in the family. Intrafamilial clinical heterogeneity suggests that other factors might be involved, such as additional variants in TBX4 or in other modifier genes. Interestingly, we identified three additional variants in the TBX4 gene in the proband only, whose phenotype is more severe. Despite being classified as benign, one of these variants is predicted to disrupt a splicing protein binding site, and may therefore affect TBX4 alternative splicing, accounting for the more severe phenotype of the proband. We expand and further delineate the genotypic and phenotypic spectrum of ICPPS. Further studies are necessary to shed light on the potential effect of this variant and on the variable phenotypic expressivity of TBX4-related phenotypes.

A novel pathogenic variant in ALAS2 gene in young Indian male with X-linked sideroblastic anemia: a case report

BackgroundCongenital sideroblastic anemias are heterogenous disorders with variable phenotypic expression. The most common form is X-linked and is caused by pathogenic variants of the 5-aminolevulinate synthase 2 (ALAS2) enzyme of heme biosynthesis.Case presentationA 19 year old Indian young male presented with severe microcytic anemia. Bone marrow examination revealed ring sideroblasts. Using second generation sequencing, a novel pathogenic variant (Arg204Leu) was found in exon 5 of the ALAS2 gene, establishing the diagnosis of X-linked sideroblastic anemia. On treatment with oral pyridoxine supplement the patient’s hemoglobin level returned to normal.ConclusionsMore than 100 pathogenic variants in the ALAS2 gene have been reported to date. The Arg204Leu variant in our case adds to the XLSA pathogenic variant data base. The associated anemia is fully responsive to pyridoxine supplementation.

Fine‐scale phenotypic variation of a large herbivore in a pulsed environment

AbstractThe resource rule hypothesis predicts that geographic differences in body size among populations of organisms are due to the amount, availability, and quality of food resources. For instance, the body size of large herbivores is often correlated with soil characteristics because better soils produce better forage. In semiarid environments, rainfall variation is an important driver of forage availability, especially highly nutritious annual forbs. Thus, in such pulsed‐resource environments, it is unclear whether the body size of large herbivores is influenced by fixed resources correlated with soil characteristics, irregular resource pulses correlated with rainfall, or both. Furthermore, it is not clear whether phenotypic expression is a function of forage quality or quantity. During the early autumns of 2011–2018, we captured 4554 white‐tailed deer (Odocoileus virginianus) on seven rangeland sites in the semiarid climate of South Texas, USA. The sites range from coastal to 140 km inland and represent gradients in both soil texture and annual rainfall. We recorded age‐ and sex‐specific indices of skeletal size, antler size, and body mass. Site‐specific soil characteristics explained most of the variation in skeletal size; percent sand was inversely related to skeletal size. For environmentally sensitive phenotypes (antler size and body mass), both soil characteristics and rainfall were influencers; increases in rainfall reduced the negative effect of sand. Percent sand and rainfall were positively correlated with annual biomass of preferred forbs, yet all phenotypic traits declined with increases in forb quantity. Increases in percent shrub cover increased all phenotype sizes. Our data suggest that the phenotypic expression of large herbivores in semiarid environments is driven by forage quality via edaphic characteristics rather than forage quantity via rainfall. Specifically, less sand in the soil allows for the development of shrub communities, which in turn provide a consistent source of forage in a variable, pulsed‐rainfall environment. Although forbs are of higher quality, they are highly ephemeral. The availability of a consistent source of forage may enable white‐tailed deer to extend time invested in body growth, which results in greater phenotype size. Our findings align with the resource rule hypothesis that identifies resource availability as a fundamental element explaining geographical variation in phenotypic expression.

Cardiomyopathy and Sudden Cardiac Death: Bridging Clinical Practice with Cutting-Edge Research.

Sudden cardiac death (SCD) prevention in cardiomyopathies such as hypertrophic (HCM), dilated (DCM), non-dilated left ventricular (NDLCM), and arrhythmogenic right ventricular cardiomyopathy (ARVC) remains a crucial but complex clinical challenge, especially among younger populations. Accurate risk stratification is hampered by the variability in phenotypic expression and genetic heterogeneity inherent in these conditions. This article explores the multifaceted strategies for preventing SCD across a spectrum of cardiomyopathies and emphasizes the integration of clinical evaluations, genetic insights, and advanced imaging techniques such as cardiac magnetic resonance (CMR) in assessing SCD risks. Advanced imaging, particularly CMR, not only enhances our understanding of myocardial architecture but also serves as a cornerstone for identifying at-risk patients. The integration of new research findings with current practices is essential for advancing patient care and improving survival rates among those at the highest risk of SCD. This review calls for ongoing research to refine risk stratification models and enhance the predictive accuracy of both clinical and imaging techniques in the management of cardiomyopathies.

Phenotypic spectrum of the first Belgian MYBPC3 founder: a large multi-exon deletion with a varying phenotype.

Variants in the MYBPC3 gene are a frequent cause of hypertrophic cardiomyopathy (HCM) but display a large phenotypic heterogeneity. Founder mutations are often believed to be more benign as they prevailed despite potential negative selection pressure. We detected a pathogenic variant in MYBPC3 (del exon 23-26) in several probands. We aimed to assess the presence of a common haplotype and to describe the cardiac characteristics, disease severity and long-term outcome of mutation carriers. Probands with HCM caused by a pathogenic deletion of exon 23-26 of MYBPC3 were identified through genetic screening using a gene panel encompassing 59 genes associated with cardiomyopathies in a single genetic center in Belgium. Cascade screening of first-degree relatives was performed, and genotype positive relatives were further phenotyped. Clinical characteristics were collected from probands and relatives. Cardiac outcomes included death, heart transplantation, life-threatening arrhythmia, heart failure hospitalization or septal reduction therapy. Haplotype analysis, using microsatellite markers surrounding MYBPC3, was performed in all index patients to identify a common haplotype. The age of the founder variant was estimated based on the size of the shared haplotype using a linkage-disequilibrium based approach. We identified 24 probands with HCM harbouring the MYBPC3 exon 23-26 deletion. Probands were on average 51 ± 16years old at time of clinical HCM diagnosis and 62 ± 10 years old at time of genetic diagnosis. A common haplotype of 1.19Mb was identified in all 24 probands, with 19 of the probands sharing a 13.8Mb haplotype. The founder event was estimated to have happened five generations, or 175-200years ago, around the year 1830 in central Flanders. Through cascade screening, 59 first-degree relatives were genetically tested, of whom 37 (62.7%) were genotype positive (G+) and 22 (37.3%) genotype negative (G-). They were on average 38 ± 19years old at time of genetic testing. Subsequent clinical assessment revealed a HCM phenotype in 19 (51.4%) G+ relatives. Probands were older (63 ± 10 vs. 42 ± 21years; p < 0.001) and had more severe phenotypes than G+ family members, presenting with more symptoms (50% vs. 13.5%; p = 0.002), arrhythmia (41.7% vs. 12.9%, p = 0.014), more overt hypertrophy and left ventricular outflow tract obstruction (43.5% vs. 3.0%; p < 0.001). Male G+ relatives more often had a HCM phenotype (78.6% vs. 34.8%; p = 0.010) and were more severely affected than females. At the age of 50, a penetrance of 78.6% was observed, defined as the presence of HCM in 11 of 14 G+ relatives with age ≥50years. Overall, 20.3% of all variant carriers developed one of the predefined cardiac outcomes after a median follow-up of 5.5years with an average age of 50 (±21) years. A Belgian founder variant, an exon 23-26 deletion in MYBPC3, was identified in 24 probands and 37 family members. The variant is characterized by a high penetrance of 78.6% at the age of 50years but has variable phenotypic expression. Adverse outcomes were observed in 20.3% of patients during follow-up.

Exceptional observation of congenital hyperinsulinism with variable phenotypic expression

Exceptional observation of congenital hyperinsulinism with variable phenotypic expression

Arrhythmogenic Left Ventricular Cardiomyopathy: From Diagnosis to Risk Management.

Left ventricular arrhythmogenic cardiomyopathy (ALVC) is a rare and poorly characterized cardiomyopathy that has recently been reclassified in the group of non-dilated left ventricular cardiomyopathies. This review aims to summarize the background, diagnosis, and sudden cardiac death risk in patients presenting this cardiomyopathy. Although there is currently a lack of data on this condition, arrhythmogenic left ventricular dysplasia can be considered a specific disease of the left ventricle (LV). We have collected the latest evidence about the management and the risks associated with this cardiomyopathy. Left ventricular arrhythmogenic cardiomyopathy is still poorly characterized. ALVC is characterized by fibrofatty replacement in the left ventricular myocardium, with variable phenotypic expression. Diagnosis is based on a multiparametric approach, including cardiac magnetic resonance (CMR) and genetic testing, and is important for sudden cardiac death (SCD) risk stratification and management. Recent guidelines have improved the management of left ventricular arrhythmogenic cardiomyopathy. Further studies are necessary to improve knowledge of this cardiomyopathy.

Novel JAG1 variants leading to Alagille syndrome in two Chinese cases

Alagille Syndrome (ALGS) is a complex genetic disorder characterized by cholestasis, congenital cardiac anomalies, and butterfly vertebrae. The variable phenotypic expression of ALGS can lead to challenges in accurately diagnosing affected infants, potentially resulting in misdiagnoses or underdiagnoses. This study highlights novel JAG1 gene mutations in two cases of ALGS. The first case with a novel p.Pro325Leufs*87 variant was diagnosed at 2 months of age and exhibited a favorable prognosis and an unexpected manifestation of congenital hypothyroidism. Before the age of 2, the second patient was incorrectly diagnosed with liver structural abnormalities, necessitating extensive treatment. In addition, he exhibited delays in language acquisition that may have been a result of SNAP25 haploinsufficiency. The identification of ALGS remains challenging, highlighting the importance of early detection and genetic testing for effective patient management. The variant p.Pro325Leufs*87 is distinct from reported variants linked to congenital hypothyroidism in ALGS patients, thereby further confirming the clinical and genetic complexity of ALGS. This emphasizes the critical need for individualized and innovative approaches to diagnosis and medical interventions, uniquely intended to address the complexity of this syndrome.

Increased Activated Protein C Response Rates to Thrombin Formation in Asymptomatic Factor V Leiden Carriers Are Driven By the Endothelium

Background The thrombophilic factor V Leiden (FVL) mutation shows a highly variable clinical expressivity. We have shown in vivo that asymptomatic FVL carriers respond to extrinsic coagulation activation with higher activated protein C (APC) formation rates than those with a history of venous thromboembolism (VTE). Recently we have established an ex vivo model for personalized assessment of the protein C (PC) pathway combining endothelial colony forming cells (ECFCs) and autologous plasma. Aim of this study was to investigate potential modulating factors of the APC response in the endothelium unraveling the enigma of the variable expressivity of the FVL phenotype. Methods ECFCs were isolated from FVL carriers with (FVL VTE+) or without (FVL VTE-) a history of unprovoked VTE and healthy controls (non-FVL) (n=7 each). Quality control of cultured cells included cobblestone morphology as examined by light microscopy, positive staining for CD31, CD309, CD201, and CD141, CD34, and negative staining for CD45 analyzed by flow cytometry. We either added autologous or pooled normal defibrinated plasma to the confluent cell culture and inititated thrombin formation by addition of tissue factor (1 pmol/L) and CaCl 2 (16.6 mmol/L) ( Fig. 1A). Thrombin and APC formation were measured over time using oligonucleotide-based enzyme capture assays (OECAs) and the ratio between the area under the curve (AUC) of APC formation and the AUC of thrombin formation was calculated as measure for APC response to thrombin. Moreover, we quantified thrombomodulin (TM) and endothelial protein C receptor (EPCR) expression in cell-based enzyme-linked immunosorbent assays (cell-ELISAs) and measured activation of purified PC on ECFCs in the APC-OECA. Results ECFC morphology in light microscopy and characteristic surface marker expression in flow cytometry did not differ between non-FVL, FVL VTE-, and FVL VTE+ subgroups. In the ECFC-based ex vivo model, the APC response in plasma on autologous cells was significantly higher in asymptomatic FVL VTE- carriers compared to non-FVL carriers (P = .0072) and compared to the FVL VTE+ subgroup (P = .0292) whereas it did not differ significantly between non-FVL and FVL VTE+ carriers. EPCR expression on ECFCs measured by cell-ELISA was higher in non-FVL carriers compared to FVL VTE+ subjects (P = .0374) but did not differ significantly when comparing non-FVL versus FVL VTE-, and FVL VTE+ versus FVL VTE-. Similarly, we showed that TM expression as well as activation of purified PC on ECFCs did not differ between cohorts. However, when the APC response was assessed on FVL VTE- and FVL VTE+ ECFCs using non-FVL plasma, the difference in the APC response between asymptomatic FVL carriers and FVL carriers with a history of VTE persisted (P = .0111) ( Fig. 1B). Conclusion Consistent with previous in vivo experiments, APC response rates to thrombin formation were increased on ECFCs obtained from asymptomatic FVL carriers compared to those from FVL carriers with a history of VTE in autologous plasma. Although TM and EPCR expression did not differ between both groups, we showed that the endothelial APC response in asymptomatic FVL carriers remained increased when using plasma from healthy controls. Our observations suggest that the increased APC response to thrombin in asymptomatic FVL carriers is driven by the endothelium. Further studies are warranted to elucidate the underlying mechanism for a better understanding of endogenous protective factors in FVL carriers. These findings may pave the way towards personalized, precision medicine approaches for managing the thrombotic risk in FVL and other disorders related to the PC pathway.

Characterization of heterozygous and homozygous mouse models with the most common hypertrophic cardiomyopathy mutation MYBPC3c.2373InsG in the Netherlands

Hypertrophic cardiomyopathy (HCM) is frequently caused by mutations in the cardiac myosin binding protein-C (cMyBP-C) encoding gene MYBPC3. In the Netherlands, approximately 25% of patients carry the MYBPC3c.2373InsG founder mutation. Most patients are heterozygous (MYBPC3+/InsG) and have highly variable phenotypic expression, whereas homozygous (MYBPC3InsG/InsG) patients have severe HCM at a young age. To improve understanding of disease progression and genotype-phenotype relationship based on the hallmarks of human HCM, we characterized mice with CRISPR/Cas9-induced heterozygous and homozygous mutations. At 18–28 weeks of age, we assessed the cardiac phenotype of Mybpc3+/InsG and Mybpc3InsG/InsG mice with echocardiography, and performed histological analyses. Cytoskeletal proteins and cardiomyocyte contractility of 3–4 week old and 18–28 week old Mybpc3c.2373InsG mice were compared to wild-type (WT) mice. Expectedly, knock-in of Mybpc3c.2373InsG resulted in the absence of cMyBP-C and our 18–28 week old homozygous Mybpc3c.2373InsG model developed cardiac hypertrophy and severe left ventricular systolic and diastolic dysfunction, whereas HCM was not evident in Mybpc3+/InsG mice. Mybpc3InsG/InsG cardiomyocytes also presented with slowed contraction-relaxation kinetics, to a greater extent in 18–28 week old mice, partially due to increased levels of detyrosinated tubulin and desmin, and reduced cardiac troponin I (cTnI) phosphorylation. Impaired cardiomyocyte contraction-relaxation kinetics were successfully normalized in 18–28 week old Mybpc3InsG/InsG cardiomyocytes by combining detyrosination inhibitor parthenolide and β-adrenergic receptor agonist isoproterenol. Both the 3–4 week old and 18–28 week old Mybpc3InsG/InsG models recapitulate HCM, with a severe phenotype present in the 18–28 week old model.

SAT084 Maternally Inherited Diabetes With Deafness: A Rare And Challenging Diagnosis Of Diabetes

Abstract Disclosure: K. Cuan: None. I.R. Bass: None. Introduction: Maternally inherited diabetes with deafness (MIDD) is a rare mitochondrial disease with variable phenotypic expression characterized by a defect in insulin secretion and sensorineural hearing loss. Other potential features of MIDD include proximal myopathy, macular retinal dystrophy, and renal focal segmental glomerulosclerosis. Mitochondrial diseases are difficult to recognize given their heterogeneous presentation, however accurate diagnosis of MIDD is important as there are implications for management. DESCRIPTION: A 38-year-old adopted woman with previously diagnosed type 1 diabetes (T1DM), congenital deafness, and chronic kidney disease presented to our endocrinology clinic with concerns for difficulty controlling her blood glucose levels. She was diagnosed with T1DM at age 21 based on age and normal body habitus and was started on insulin. Due to insurance issues, she discontinued insulin use for several years and her diabetes was poorly controlled during that time, however, she never experienced diabetic ketoacidosis (DKA). Upon resuming insulin, she experienced multiple unpredictable episodes of hypoglycemia and subsequently self-discontinued insulin and presented 8 months later for further care. Past history was notable for muscle weakness with walking upstairs and vision loss in her left eye, which led to a diagnosis of retinopathy in her early twenties. Her family history was unavailable as she was adopted. Her physical exam was significant for a normal body mass index of 24. Labs showed a hemoglobin A1C of 10.8% and detectable c-peptide, 2.7 ng/mL (1.1-4.4 ng/mL) with a glucose of 192mg/dL. Glutamic acid decarboxylase, zinc transporter 8, IA-2 and islet-cell antibodies were all negative. Her creatinine was 1.23 ng/dL with a severely increased microalbumin to creatinine ratio (638, 0-29 mg/g). In view of her congenital deafness, non-diabetic retinopathy, absence of DKA while off insulin, negative antibody testing, and chronic kidney disease, mitochondrial diabetes was considered. She was referred to a geneticist for mitochondrial genome sequencing, of which the results are pending. Dietary modification and oral agents were recommended for her diabetes management, rather than insulin therapy. DISCUSSION: MIDD can be challenging to diagnose and patients may be incorrectly labeled as having type 1 diabetes. The presence of maternal transmission can aid in the diagnosis of MIDD, however, our patient was adopted and this information is unavailable. Additionally, retinal and renal features of MIDD can be misconstrued as microvascular complications of diabetes. In patients with deafness and poorly controlled diabetes with negative antibody testing, MIDD should be considered as an alternative diagnosis. MIDD can be managed with dietary modification, oral agents, and insulin if appropriate. Presentation: Saturday, June 17, 2023

A recurrent KCNK4 variant in a dominant pedigree with hypertrichosis and gingival fibromatosis syndrome: Variable phenotypic expressivity and insights on patients' dental management.

Abnormal hyperpolarization of the KCNK4 gene, expressed in the nervous system, brain, and periodontal ligament fibroblasts, leads to impaired neurotransmitter sensitivity, cardiac arrhythmias, and endocrine dysfunction, as well as, progressive cell proliferation. De novo gain of function variants in the KCNK4 gene were reported to cause a recognizable syndrome characterized by facial dysmorphism, hypertrichosis, epilepsy, intellectual/developmental delay, and gingival overgrowth (FHEIG, OMIM# 618381). FHEIG is extremely rare with only three reported cases in the literature. Herein, we describe the first inherited KCNK4 variant (c.730G>C, p.Ala244Pro) in an Egyptian boy and his mother. Variable phenotypic expressivity was noted as the patient presented with the full-blown picture of the syndrome while the mother presented only with hypertrichosis and gingival overgrowth without any neurological manifestations. The c.730G>C (p.Ala244Pro) variant was described before in a single patient and when comparing the phenotype with our patient, a phenotype-genotype correlation seems likely. Atrial fibrillation and joint laxity are new associated findings noted in our patient extending the clinical phenotype of the syndrome. Dental management was offered to the affected boy and a dramatic improvement was noted as the patient regained his smile, restored the mastication function, and resumed his psychological stability.

Clinical Characterization of Alagille Syndrome in Patients with Cholestatic Liver Disease.

Alagille syndrome (ALGS) is a multisystem condition characterized by cholestasis and bile duct paucity on liver biopsy and variable involvement of the heart, skeleton, eyes, kidneys, and face and caused by pathogenic variants in the JAG1 or NOTCH2 gene. The variable expressivity of the clinical phenotype and the lack of genotype-phenotype correlations lead to significant diagnostic difficulties. Here we present an analysis of 18 patients with cholestasis who were diagnosed with ALGS. We used an NGS panel targeting coding exons of 52 genes, including the JAG1 and NOTCH2 genes. Sanger sequencing was used to verify the mutation in the affected individuals and family members. The specific facial phenotype was seen in 16/18 (88.9%). Heart defects were seen in 8/18 (44.4%) patients (pulmonary stenosis in 7/8). Butterfly vertebrae were seen in 5/14 (35.7%) patients. Renal involvement was detected in 2/18 (11.1%) cases-one patient had renal cysts, and one had obstructive hydronephrosis. An ophthalmology examination was performed on 12 children, and only one had posterior embryotoxon (8.3%). A percutaneous liver biopsy was performed in nine cases. Bile duct paucity was detected in six/nine cases (66.7%). Two patients required liver transplantation because of cirrhosis. We identified nine novel variants in the JAG1 gene-eight frameshift variants (c.1619_1622dupGCTA (p.Tyr541X), c.1160delG (p.Gly387fs), c.964dupT (p.C322fs), c.120delG (p.L40fs), c.1984dupG (p.Ala662Glyfs), c.3168_3169delAG (p.R1056Sfs*51), c.2688delG (p.896CysfsTer49), c.164dupG (p.Cys55fs)) and one missense variant, c.2806T > G (p.Cys936Gly). None of the patients presented with NOTCH2 variants. In accordance with the classical criteria, only six patients could meet the diagnostic criteria in our cohort without genetic analysis. Genetic testing is important in the diagnosis of ALGS and can help differentiate it from other types of cholestasis.

Identification of a novel PTH1R variant in a family with primary failure of eruption

BackgroundPrimary failure of tooth eruption (PFE) is a rare autosome genetic disorder that causes open bite. This work aimed to report a small family of PFE(OMIM: # 125,350) with a novel PTH1R variant. One of the patients has a rare clinical phenotype of the anterior tooth involved only.Case presentationThe proband was a 13-year-old young man with an incomplete eruption of the right upper anterior teeth, resulting in a significant open-bite. His left first molar partially erupted. Family history revealed that the proband’s 12-year-old brother and father also had teeth eruption disorders. Genetic testing found a novel PTH1R variant (NM_000316.3 c.1325-1336del), which has never been reported before. The diagnosis of PFE was based on clinical and radiographic characteristics and the result of genetic testing. Bioinformatic analysis predicted this variant would result in the truncation of the G protein-coupled receptor encoded by the PTH1R, affecting its structure and function.ConclusionA novel PTH1R variant identified through whole-exome sequencing further expands the mutation spectrum of PFE. Patients in this family have different phenotypes, which reflects the characteristics of variable phenotypic expression of PFE.

Novel environments induce variability in fitness-related traits.

Environmental change from anthropogenic activities threatens individual organisms, the persistence of populations, and entire species. Rapid environmental change puts organisms in a double bind, they are forced to contend with novel environmental conditions but with little time to respond. Phenotypic plasticity can act quickly to promote establishment and persistence of individuals and populations in novel or altered environments. In typical environmental conditions, fitness-related traits can be buffered, reducing phenotypic variation in expression of traits, and allowing underlying genetic variation to accumulate without selection. In stressful conditions, buffering mechanisms can break down, exposing underlying phenotypic variation, and permitting the expression of phenotypes that may allow populations to persist in the face of altered or otherwise novel environments. Using reciprocal transplant experiments of freshwater snails, we demonstrate that novel conditions induce higher variability in growth rates and, to a lesser degree, morphology (area of the shell opening) relative to natal conditions. Our findings suggest a potentially important role of phenotypic plasticity in population persistence as organisms face a rapidly changing, human-altered world.

Hereditary hemochromatosis: An update vision of the laboratory diagnosis

Haemochromatosis (HC) is an inherited disorder of iron metabolism. The 85–90% of Hereditary hemochromatosis cases are caused by mutations in HFE gene (HC type 1). The remaining 10–15% of HC cases are caused by mutations in other non-HFE genes (HJV, HAMP, TRF2, SLC40A1, BMP6). The study of patients for the diagnosis of HC has an important laboratory approached: analysis of biochemical parameters and genetic studies. To confirm a case, it is necessary to carry out a genetic study of the C282Y and H63D mutations. The presence of C282Y mutation in homozygosis is compatible with the diagnosis of HC type 1. Due to the incomplete penetrance of this mutation and the variable phenotypic expression, the severe forms of the disease are relatively rare. The study of variants in non-HFE genes allows more detailed study of both non-classic HC cases and those with more severe clinical expression. The genotype characterization of a patient not always justified the phenotype expression of the symptoms in this disease. All laboratory clinicians must consider recommendation provide by the experts in the Materia.

DNA methylation differences in monozygotic twins with Van der Woude syndrome.

Van der Woude Syndrome (VWS) is an autosomal dominant disorder responsible for 2% of all syndromic orofacial clefts (OFCs) with IRF6 being the primary causal gene (70%). Cases may present with lip pits and either cleft lip, cleft lip with cleft palate, or cleft palate, with marked phenotypic discordance even among individuals carrying the same mutation. This suggests that genetic or epigenetic modifiers may play additional roles in the syndrome's etiology and variability in expression. We report the first DNA methylation profiling of 2 pairs of monozygotic twins with VWS. Our goal is to explore epigenetic contributions to VWS etiology and variable phenotypic expressivity by comparing DNAm profiles in both twin pairs. While the mutations that cause VWS in these twins are known, the additional mechanism behind their phenotypic risk and variability in expression remains unclear. We generated whole genome DNAm data for both twin pairs. Differentially methylated positions (DMPs) were selected based on: (1) a coefficient of variation in DNAm levels in unaffected individuals < 20%, and (2) intra-twin pair absolute difference in DNAm levels >5% (delta beta > | 0.05|). We then divided the DMPs in two subgroups for each twin pair for further analysis: (1) higher methylation levels in twin A (Twin A > Twin B); and (2) higher methylation levels in twin B (Twin B >Twin A). Gene ontology analysis revealed a list of enriched genes that showed significant differential DNAm, including clef-associated genes. Among the cleft-associated genes, TP63 was the most significant hit (p=7.82E-12). Both twin pairs presented differential DNAm levels in CpG sites in/near TP63 (Twin 1A > Twin 1B and Twin 2A < Twin 2B). The genes TP63 and IRF6 function in a biological regulatory loop to coordinate epithelial proliferation and differentiation in a process that is critical for palatal fusion. The effects of the causal mutations in IRF6 can be further impacted by epigenetic dysregulation of IRF6 itself, or genes in its pathway. Our data shows evidence that changes in DNAm is a plausible mechanism that can lead to markedly distinct phenotypes, even among individuals carrying the same mutation.

363 - Holt-oram syndrome and its variable phenotypic expression: a multi-generational case series

363 - Holt-oram syndrome and its variable phenotypic expression: a multi-generational case series

Utility of Whole Exome Sequencing in the Early Diagnosis of Atypical Diamond-Blackfan Anemia.

Diamond-Blackfan anemia (DBA) is a rare congenital bone marrow failure syndrome, with a hallmark of erythroblastopenia and congenital anomalies. DBA demonstrates genetic heterogeneity and variable phenotypic expression. We present two cases of atypical DBA harboring de novo mutations in the RPS-19 gene with c.49 G>C and c.357-1G>T allelic variants. The two cases presented confounding critical illness demonstrated by multiorgan failure, aplastic crisis, with case 2 meeting the criteria for hemophagocytic lymphohistiocytosis. We highlight the utility of genetic testing in the early diagnosis of DBA and the associated complexities and burden of disease in caring for DBA patients.

Autosomal recessive Noonan-like syndrome caused by homozygosity for a previously unreported variant in SPRED2

Noonan syndrome is characterized by variable phenotypic expressivity with characteristic dysmorphic facial features, varying degrees of intellectual disability, developmental delay, short stature, and congenital heart defects in 50–80%. Other findings include a webbed neck, cryptorchidism, coagulation defects and eye abnormalities.Thus far, Noonan syndrome has mainly been attributed to heterozygous pathogenic variants in 10+ different genes, with the rare exception of cases due to biallelic pathogenic variants in LZTR1. Recently, homozygous loss-of-function variants in SPRED2 have been identified as a cause of a recessive Noonan syndrome-like phenotype. We present the phenotypes of two additional patients with homozygosity for a previously unreported loss-of-function variant in SPRED2, thereby adding relevant clinical information about the recently described Noonan syndrome-like SPRED2-related phenotype.