Isolated- and Beckwith-Wiedemann syndrome related- lateralised overgrowth (hemihypertrophy): Clinical and molecular correlations in 94 individuals

The congenital imprinting disorder, Beckwith-Wiedemann syndrome (BWS) is associated with variable clinical features including hemihypertrophy/lateralised overgrowth (LO) and embryonal tumour predisposition. BWS-associated (epi)genetic alterations occur in a subset of patients with isolated LO (ILO), leading to the concept of BWS spectrum disorder (BWSp). We investigated the relationship between clinical features and molecular diagnostic results in a cohort with LO using the BWSp international consensus group (BWSICG) clinical scoring system. Clinical/molecular findings in 94 previously-unreported patients with LO referred for BWSp molecular studies were reviewed retrospectively. The BWSICG score was assigned and diagnostic rate calculated. BWSp-associated (epi)genetic alteration was identified in 15/94 (16%). The molecular diagnostic rate by MS-MLPA (blood DNA) for BWS-related molecular findings in patients with LO was positively correlated with the BWSICG score. 3/48 with ILO had a molecular alteration. No individuals with ILO had developed an embryonal tumour at last follow up. Among a cohort of individuals with LO referred for BWSp molecular testing, the BWSICG score correlated with diagnostic yield. The embryonal tumour risk in children with ILO and negative molecular testing appeared very low, however longer- and more complete follow up is required to better define tumour risks in this group.

Non-coding region variants upstream of MEF2C cause severe developmental disorder through three distinct loss-of-function mechanisms

Clinical genetic testing of protein-coding regions identifies a likely causative variant in only around half of developmental disorder (DD) cases. The contribution of regulatory variation in non-coding regions to rare disease, including DD, remains very poorly understood. We screened 9,858 probands from the Deciphering Developmental Disorders (DDD) study for de novo mutations in the 5' untranslated regions (5' UTRs) of genes within which variants have previously been shown to cause DD through a dominant haploinsufficient mechanism. We identified four single-nucleotide variants and two copy-number variants upstream of MEF2C in a total of ten individual probands. We developed multiple bespoke and orthogonal experimental approaches to demonstrate that these variants cause DD through three distinct loss-of-function mechanisms, disrupting transcription, translation, and/or protein function. These non-coding region variants represent 23% of likely diagnoses identified in MEF2C in the DDD cohort, but these would all be missed in standard clinical genetics approaches. Nonetheless, these variants are readily detectable in exome sequence data, with 30.7% of 5' UTR bases across all genes well covered in the DDD dataset. Our analyses show that non-coding variants upstream of genes within which coding variants are known to cause DD are an important cause of severe disease and demonstrate that analyzing 5' UTRs can increase diagnostic yield. We also show how non-coding variants can help inform both the disease-causing mechanism underlying protein-coding variants and dosage tolerance of the gene.

Telemedicine strategy of the European Reference Network ITHACA for the diagnosis and management of patients with rare developmental disorders

BACKGROUND

The European Reference Networks, ERNs, are virtual networks for healthcare providers across Europe to collaborate and share expertise on complex or rare diseases and conditions. As part of the ERNs, the Clinical Patient Management System, CPMS, a secure digital platform, was developed to allow and facilitate web-based, clinical consultations between submitting clinicians and relevant international experts. The European Reference Network on Intellectual Disability, TeleHealth and Congenital Anomalies, ERN ITHACA, was formed to harness the clinical and diagnostic expertise in the sector of rare, multiple anomaly and/or intellectual disability syndromes, chromosome disorders and undiagnosed syndromic disorders. We present the first year results of CPMS use by ERN ITHACA as an example of a telemedicine strategy for the diagnosis and management of patients with rare developmental disorders.

RESULTS

ERN ITHACA ranked third in telemedicine activity amongst 24 European networks after 12 months of using the CPMS. Information about 28 very rare cases from 13 different centres across 7 countries was shared on the platform, with diagnostic or other management queries. Early interaction with patient support groups identified data protection as of primary importance in adopting digital platforms for patient diagnosis and care. The first launch of the CPMS was built to accommodate the needs of all ERNs. The ERN ITHACA telemedicine process highlighted a need to customise the CPMS with network-specific requirements. The results of this effort should enhance the CPMS utility for telemedicine services and ERN-specific care outcomes.

CONCLUSIONS

We present the results of a long and fruitful process of interaction between the ERN ITHACA network lead team and EU officials, software developers and members of 38 EU clinical genetics centres to organise and coordinate direct e-healthcare through a secure, digital platform. The variability of the queries in just the first 28 cases submitted to the ERN ITHACA CPMS is a fair representation of the complexity and rarity of the patients referred, but also proof of the sophisticated and variable service that could be provided through a structured telemedicine approach for patients and families with rare developmental disorders. Web-based approaches are likely to result in increased accessibility to clinical genomic services.

Delineation of dominant and recessive forms of LZTR1-associated Noonan syndrome

Noonan syndrome (NS) is characterised by distinctive facial features, heart defects, variable degrees of intellectual disability and other phenotypic manifestations. Although the mode of inheritance is typically dominant, recent studies indicate LZTR1 may be associated with both dominant and recessive forms. Seeking to describe the phenotypic characteristics of LZTR1-associated NS, we searched for likely pathogenic variants using two approaches. First, scrutiny of exomes from 9624 patients recruited by the Deciphering Developmental Disorders (DDDs) study uncovered six dominantly-acting mutations (p.R97L; p.Y136C; p.Y136H, p.N145I, p.S244C; p.G248R) of which five arose de novo, and three patients with compound-heterozygous variants (p.R210*/p.V579M; p.R210*/p.D531N; c.1149+1G>T/p.R688C). One patient also had biallelic loss-of-function mutations in NEB, consistent with a composite phenotype. After removing this complex case, analysis of human phenotype ontology terms indicated significant phenotypic similarities (P = 0.0005), supporting a causal role for LZTR1. Second, targeted sequencing of eight unsolved NS-like cases identified biallelic LZTR1 variants in three further subjects (p.W469*/p.Y749C, p.W437*/c.-38T>A and p.A461D/p.I462T). Our study strengthens the association of LZTR1 with NS, with de novo mutations clustering around the KT1-4 domains. Although LZTR1 variants explain ~0.1% of cases across the DDD cohort, the gene is a relatively common cause of unsolved NS cases where recessive inheritance is suspected.