Pathogenic variants in HGF give rise to childhood-to-late onset primary lymphoedema by loss of function.

Developmental and functional defects in the lymphatic system are responsible for primary lymphoedema (PL). PL is a chronic debilitating disease caused by increased accumulation of interstitial fluid, predisposing to inflammation, infections and fibrosis. There is no cure, only symptomatic treatment is available. Thirty-two genes or loci have been linked to PL, and another 22 are suggested, including Hepatocyte Growth Factor (HGF). We searched for HGF variants in 770 index patients from the Brussels PL cohort. We identified ten variants predicted to cause HGF loss-of-function (six nonsense, two frameshifts, and two splice-site changes; 1.3% of our cohort), and 14 missense variants predicted to be pathogenic in 17 families (2.21%). We studied co-segregation within families, mRNA stability for non-sense variants, and in vitro functional effects of the missense variants. Analyses of the mRNA of patient cells revealed degradation of the nonsense mutant allele. Reduced protein secretion was detected for nine of the 14 missense variants expressed in COS-7 cells. Stimulation of lymphatic endothelial cells with these 14 HGF variant proteins resulted in decreased activation of the downstream targets AKT and ERK1/2 for three of them. Clinically, HGF-associated PL was diverse, but predominantly bilateral in the lower limbs with onset varying from early childhood to adulthood. Finally, aggregation study in a second independent cohort underscored that rare likely pathogenic variants in HGF explain about 2% of PL. Therefore, HGF signalling seems crucial for lymphatic development and/or maintenance in human beings and HGF should be included in diagnostic genetic screens for PL.

Germline ERG haploinsufficiency defines a new syndrome with cytopenia and hematological malignancy predisposition.

The genomics era has facilitated discovery of new genes predisposing to bone marrow failure (BMF) and hematological malignancy (HM). We report the discovery of ERG as a novel autosomal dominant BMF/HM predisposition gene. ERG is a highly constrained transcription factor critical for definitive hematopoiesis, stem cell function and platelet maintenance. ERG colocalizes with other transcription factors including RUNX1 and GATA2 on promoters/enhancers of genes orchestrating hematopoiesis. We identified a rare heterozygous ERG missense variant in 3 thrombocytopenic individuals from one family and 14 additional ERG variants in unrelated individuals with BMF/HM including 2 de novo cases and 3 truncating variants. Phenotypes associated with pathogenic germline ERG variants included cytopenias (thrombocytopenia, neutropenia, pancytopenia) and HMs (acute myeloid leukemia, myelodysplastic syndrome, acute lymphoblastic leukemia) with onset before 40 years. Twenty ERG variants (19 missense, 1 truncating) including 3 missense population variants were functionally characterized. Thirteen potentially pathogenic ETS domain missense variants displayed loss-of-function characteristics disrupting transcriptional transactivation, DNA-binding and/or nuclear localization. Selected variants overexpressed in mouse fetal liver cells failed to drive myeloid differentiation and cytokine-independent growth in culture, and to promote acute erythroleukemia when transplanted into mice, concordant with these variants being loss-of-function. Four individuals displayed somatic genetic rescue by copy neutral loss of heterozygosity. Identification of predisposing germline ERG variants has clinical implications for patient/family diagnosis, counselling, surveillance, and treatment strategies including selection of bone marrow donors or cell/gene therapy.

Biallelic variants in Plexin B2 (PLXNB2) cause amelogenesis imperfecta, hearing loss and intellectual disability.

BACKGROUND: Plexins are large transmembrane receptors for the semaphorin family of signalling proteins. Semaphorin-plexin signalling controls cellular interactions that are critical during development as well as in adult life stages. Nine plexin genes have been identified in humans, but despite the apparent importance of plexins in development, only biallelic PLXND1 and PLXNA1 variants have so far been associated with Mendelian genetic disease. METHODS: Eight individuals from six families presented with a recessively inherited variable clinical condition, with core features of amelogenesis imperfecta (AI) and sensorineural hearing loss (SNHL), with variable intellectual disability. Probands were investigated by exome or genome sequencing. Common variants and those unlikely to affect function were excluded. Variants consistent with autosomal recessive inheritance were prioritised. Variant segregation analysis was performed by Sanger sequencing. RNA expression analysis was conducted in C57Bl6 mice. RESULTS: Rare biallelic pathogenic variants in plexin B2 (PLXNB2), a large transmembrane semaphorin receptor protein, were found to segregate with disease in all six families. The variants identified include missense, nonsense, splicing changes and a multiexon deletion. Plxnb2 expression was detected in differentiating ameloblasts. CONCLUSION: We identify rare biallelic pathogenic variants in PLXNB2 as a cause of a new autosomal recessive, phenotypically diverse syndrome with AI and SNHL as core features. Intellectual disability, ocular disease, ear developmental abnormalities and lymphoedema were also present in multiple cases. The variable syndromic human phenotype overlaps with that seen in Plxnb2 knockout mice, and, together with the rarity of human PLXNB2 variants, may explain why pathogenic variants in PLXNB2 have not been reported previously.

Guidelines for the diagnosis and management of adult aplastic anaemia: A British Society for Haematology Guideline.

Pancytopenia with hypocellular bone marrow is the hallmark of aplastic anaemia (AA) and the diagnosis is confirmed after careful evaluation, following exclusion of alternate diagnosis including hypoplastic myelodysplastic syndromes. Emerging use of molecular cyto-genomics is helpful in delineating immune mediated AA from inherited bone marrow failures (IBMF). Camitta criteria is used to assess disease severity, which along with age and availability of human leucocyte antigen compatible donor are determinants for therapeutic decisions. Supportive care with blood and platelet transfusion support, along with anti-microbial prophylaxis and prompt management of opportunistic infections remain key throughout the disease course. The standard first-line treatment for newly diagnosed acquired severe/very severe AA patients is horse anti-thymocyte globulin and ciclosporin-based immunosuppressive therapy (IST) with eltrombopag or allogeneic haemopoietic stem cell transplant (HSCT) from a matched sibling donor. Unrelated donor HSCT in adults should be considered after lack of response to IST, and up front for young adults with severe infections and a readily available matched unrelated donor. Management of IBMF, AA in pregnancy and in elderly require special attention. In view of the rarity of AA and complexity of management, appropriate discussion in multidisciplinary meetings and involvement of expert centres is strongly recommended to improve patient outcomes.

Moyamoya disease/cerebral vasculopathy in osteopathia striata with cranial sclerosis: a rare but important complication.

Osteopathia striata with cranial sclerosis (OSCS) is a rare X-linked dominant sclerosing osteodysplasia, due to AMER1 pathogenic variants. Characteristic features include craniofacial sclerosis and long-bone metaphyseal striations. Moyamoya disease (a type of progressive cerebral vasculopathy) and other types of cerebral vascular disease are not currently clearly associated with OSCS (except for two separate case reports), and can often first present with stroke. Through informal networks with UK-based bone experts and the UK skeletal dysplasia group, three cases from the UK and Ireland were identified. Medical literature was also reviewed to identify the known cases of OSCS with the described complications. We report four females, in whom OSCS and cerebral vasculopathy co-exist, with varying clinical outcomes. There appears to be an emerging association between OSCS and cerebral vasculopathy, which pre-disposes patients to stroke. Given this, screening OSCS patients for cerebral vasculopathy may be of value, especially pre-surgery. Further research regarding optimal screening and management is needed. The mechanism of cerebral vasculopathy and its progression remain unclear.

The VASCERN PPL working group patient pathway for primary and paediatric lymphoedema.

Lymphoedema is caused by an imbalance between fluid production and transport by the lymphatic system. This imbalance can be either caused by reduced transport capacity of the lymphatic system or too much fluid production and leads to swelling associated with tissue changes (skin thickening, fat deposition). Its main common complication is the increased risk of developing cellulitis/erysipelas in the affected area, which can worsen the lymphatic function and can be the cause of raised morbidity of the patient if not treated correctly/urgently. The term primary lymphoedema covers a group of rare conditions caused by abnormal functioning and/or development of the lymphatic system. It covers a highly heterogeneous group of conditions. An accurate diagnosis of primary lymphoedema is crucial for the implementation of an optimal treatment plan and management, as well as to reduce the risk of worsening. Patient care is diverse across Europe, and national specialised centres and networks are not available everywhere. The European Reference Network on Rare Multisystemic Vascular Diseases (VASCERN) gathers the best expertise in Europe and provide accessible cross-border healthcare to patients with rare vascular diseases. There are six different working groups in VASCERN, which focus on arterial diseases, hereditary haemorrhagic telangiectasia, neurovascular diseases, lymphoedema and vascular anomalies. The working group Paediatric and Primary Lymphedema (PPL WG) gathers and shares knowledge and expertise in the diagnosis and management of adults and children with primary and paediatric lymphoedema. The members of PPL WG have worked together to produce this opinion statement reflecting strategies on how to approach patients with primary and paediatric lymphoedema. The objective of this patient pathway is to improve patient care by reducing the time to diagnosis, define the best management and follow-up strategies and avoid overuse of resources. Therefore, the patient pathway describes the clinical evaluation and investigations that lead to a clinical diagnosis, the genetic testing, differential diagnosis, the management and treatment options and the patient follow up at expert and local centres. Also, the importance of the patient group participation in the PPL WG is discussed.

Delivery of a national prenatal exome sequencing service in England: a mixed methods study exploring healthcare professionals' views and experiences.

Introduction: In October 2020, rapid prenatal exome sequencing (pES) was introduced into routine National Health Service (NHS) care in England, requiring the coordination of care from specialist genetics, fetal medicine (FM) and laboratory services. This mixed methods study explored the experiences of professionals involved in delivering the pES service during the first 2 years of its delivery in the NHS. Methods: A survey (n = 159) and semi-structured interviews (n = 63) with healthcare professionals, including clinical geneticists, FM specialists, and clinical scientists (interviews only) were used to address: 1) Views on the pES service; 2) Capacity and resources involved in offering pES; 3) Awareness, knowledge, and educational needs; and 4) Ambitions and goals for the future. Results: Overall, professionals were positive about the pES service with 77% rating it as Good or Excellent. A number of benefits were reported, including the increased opportunity for receiving actionable results for parental decision-making, improving equity of access to genomic tests and fostering close relationships between FM and genetics departments. Nonetheless, there was evidence that the shift to offering pES in a clinical setting had brought some challenges, such as additional clinic time, administrative processes, perceived lack of autonomy in decision-making regarding pES eligibility and difficulty engaging with peripheral maternity units. Concerns were also raised about the lack of confidence and gaps in genomics knowledge amongst non-genetics professionals - especially midwives. However, the findings also highlighted value in both FM, obstetric and genetics professionals benefiting from further training with a focus on recognising and managing prenatally diagnosed genetic conditions. Conclusion: Healthcare professionals are enthusiastic about the benefits of pES, and through multi-collaborative working, have developed relationships that have contributed to effective communication across specialisms. Although limitations on resources and variation in knowledge about pES have impacted service delivery, professionals were hopeful that improvements to infrastructure and the upskilling of all professionals involved in the pathway would optimise the benefits of pES for both parents and professionals.

Strengths and challenges of the artificial intelligence in the assessment of dense breasts.

Objectives: High breast density is a risk factor for breast cancer and overlapping of glandular tissue can mask lesions thus lowering mammographic sensitivity. Also, dense breasts are more vulnerable to increase recall rate and false-positive results. New generations of artificial intelligence (AI) have been introduced to the realm of mammography. We aimed to assess the strengths and challenges of adopting artificial intelligence in reading mammograms of dense breasts. Methods: This study included 6600 mammograms of dense patterns "c" and "d" and presented 4061 breast abnormalities. All the patients were subjected to full-field digital mammography, breast ultrasound, and their mammographic images were scanned by AI software (Lunit INSIGHT MMG). Results: Diagnostic indices of the sono-mammography: a sensitivity of 98.71%, a specificity of 88.04%, a positive-predictive value of 80.16%, a negative-predictive value of 99.29%, and a diagnostic accuracy of 91.5%. AI-aided mammograms presented sensitivity of 88.29%, a specificity of 96.34%, a positive-predictive value of 92.2%, a negative-predictive value of 94.4%, and a diagnostic accuracy of 94.5% in its ability to read dense mammograms. Conclusion: Dense breasts scanned with AI showed a notable reduction of mammographic misdiagnosis. Knowledge of such software challenges would enhance its application as a decision support tool to mammography in the diagnosis of cancer. Advances in knowledge: Dense breast is challenging for radiologists and renders low sensitivity mammogram. Mammogram scanned by AI could be used to overcome such limitation, enhance the discrimination between benign and malignant breast abnormalities and the early detection of breast cancer.