Suzanne Drury

Exome sequencing for prenatal diagnosis of fetuses with sonographic abnormalities

In the absence of aneuploidy or other pathogenic cytogenetic abnormality, fetuses with increased nuchal translucency (NT ≥ 3.5 mm) and/or other sonographic abnormalities have a greater incidence of genetic syndromes, but defining the underlying pathology can be challenging. Here, we investigate the value of whole exome sequencing in fetuses with sonographic abnormalities but normal microarray analysis.

CHD2 variants are a risk factor for photosensitivity in epilepsy

Photosensitivity in epilepsy is common and has high heritability, but its genetic basis remains uncertain. Galizia et al. reveal an overrepresentation of unique variants of CHD2 — which encodes the transcriptional regulator ‘chromodomain helicase DNA-binding protein 2’ — in photosensitive epilepsies, and show that chd2 knockdown in zebrafish causes photosensitivity.

Targeted gene panel sequencing in children with very early onset inflammatory bowel disease—evaluation and prospective analysis

Background Multiple monogenetic conditions with partially overlapping phenotypes can present with inflammatory bowel disease (IBD)-like intestinal inflammation. With novel genotype-specific therapies emerging, establishing a molecular diagnosis is becoming increasingly important. Design We have introduced targeted next-generation sequencing (NGS) technology as a prospective screening tool in children with very early onset IBD (VEOIBD). We evaluated the coverage of 40 VEOIBD genes in two separate cohorts undergoing targeted gene panel sequencing (TGPS) (n=25) and whole exome sequencing (WES) (n=20). Results TGPS revealed causative mutations in four genes (IL10RA, EPCAM, TTC37 and SKIV2L) discovered unexpected phenotypes and directly influenced clinical decision making by supporting as well as avoiding haematopoietic stem cell transplantation. TGPS resulted in significantly higher median coverage when compared with WES, fewer coverage deficiencies and improved variant detection across established VEOIBD genes. Conclusions Excluding or confirming known VEOIBD genotypes should be considered early in the disease course in all cases of therapy-refractory VEOIBD, as it can have a direct impact on patient management. To combine both described NGS technologies would compensate for the limitations of WES for disease-specific application while offering the opportunity for novel gene discovery in the research setting.

Non‐invasive prenatal diagnosis for cystic fibrosis: detection of paternal mutations, exploration of patient preferences and cost analysis

We aim to develop non‐invasive prenatal diagnosis (NIPD) for cystic fibrosis (CF) and determine costs and implications for implementation.

Phenotypic and genotypic characterisation of inflammatory bowel disease presenting before the age of 2 years

Objectives: Inflammatory bowel disease [IBD] presenting in early childhood is extremely rare. More recently, progress has been made to identify children with monogenic forms of IBD predominantly presenting very early in life. In this study, we describe the heterogeneous phenotypes and genotypes of patients with IBD presenting before the age of 2 years and establish phenotypic features associated with underlying monogenicity. Methods: Phenotype data of 62 children with disease onset before the age of 2 years presenting over the past 20 years were reviewed. Children without previously established genetic diagnosis were prospectively recruited for next-generation sequencing. Results: In all, 62 patients [55% male] were identified. The median disease onset was 3 months of age (interquartile range [IQR]: 1 to 11). Conventional IBD classification only applied to 15 patients with Crohn’s disease [CD]-like [24%] and three with ulcerative colitis [UC]-like [5%] phenotype; 44 patients [71%] were diagnosed with otherwise unclassifiable IBD. Patients frequently required parenteral nutrition [40%], extensive immunosuppression [31%], haematopoietic stem-cell transplantation [29%], and abdominal surgery [19%]. In 31% of patients, underlying monogenic diseases were established [EPCAM, IL10, IL10RA, IL10RB, FOXP3, LRBA, SKIV2L, TTC37, TTC7A]. Phenotypic features significantly more prevalent in monogenic IBD were: consanguinity, disease onset before the 6th month of life, stunting, extensive intestinal disease and histological evidence of epithelial abnormalities. Conclusions: IBD in children with disease onset before the age of 2 years is frequently unclassifiable into Crohn’s disease and ulcerative colitis, particularly treatment resistant, and can be indistinguishable from monogenic diseases with IBD-like phenotype.

Non-invasive prenatal diagnosis (NIPD) for single gene disorders: cost analysis of NIPD and invasive testing pathways.

Evaluate the costs of offering non‐invasive prenatal diagnosis (NIPD) for single gene disorders compared to traditional invasive testing to inform NIPD implementation into clinical practice.

A novel heterozygous SOX2 mutation causing congenital bilateral anophthalmia, hypogonadotropic hypogonadism and growth hormone deficiency.

Heterozygous de novo mutations in SOX2 have been reported in approximately 10-20% of patients with unilateral or bilateral anophthalmia or microphthalmia. An additional phenotype of hypopituitarism, with anterior pituitary hypoplasia and hypogonadotropic hypogonadism, has been reported in patients carrying SOX2 alterations. We report a novel heterozygous mutation in the SOX2 gene in a male affected with congenital bilateral anophthalmia, hypogonadotrophic hypogonadism and growth hormone deficiency. The mutation we describe is a cytosine deletion in position 905 (c905delC) which causes frameshift and an aberrant C-terminal domain. Our report highlights the fact that subjects affected with eye anomalies and harboring SOX2 mutations are at high risk for gonadotropin deficiency, which has important implications for their clinical management.

A novel homozygous ERCC5 truncating mutation in a family with prenatal arthrogryposis-Further evidence of genotype-phenotype correlation

We report on a family with five fetuses conceived to first cousin parents presenting with abnormal ultrasound findings including contractures and microcephaly. Cerebellar hypoplasia and ventriculomegaly were also present in two and fetal edema developed in the one fetus that survived beyond 24 weeks of gestation. Linkage studies of 15 members of the family, including four affecteds, were undertaken followed by exome sequencing of one affected individual and their parents. Analysis of exome data was restricted to the 9.3 Mb largest shared region of homozygosity identified by linkage; a single novel homozygous mutation in the proband that was heterozygous in the parents (ERCC5 c.2766dupA, p.Leu923ThrfsX7) was identified. This segregated with disease. ERCC5 is a component of the nucleotide excision repair machinery and biallelic mutations in the gene have previously been associated with xeroderma pigmentosum (group G), Cockayne syndrome and the more severe cerebrooculofacioskeletal syndrome. The phenotype in the family we report on is consistent with a severe manifestation of cerebrooculofacioskeletal syndrome. Our data broaden the reported clinical spectrum of ERCC5 mutations and provide further evidence of genotype–phenotype correlation with truncating mutations being associated with severe phenotypes. They also demonstrate the molecular diagnostic power of a combined approach of linkage studies and exome sequencing in families with rare, genetically heterogeneous disorders and a well described pedigree.

Cell-Free Fetal DNA Testing for Prenatal Diagnosis

Prenatal diagnosis and screening have undergone rapid development in recent years, with advances in molecular technology driving the change. Noninvasive prenatal testing (NIPT) for Down syndrome as a highly sensitive screening test is now available worldwide through the commercial sector with many countries moving toward implementation into their publically funded maternity systems. Noninvasive prenatal diagnosis (NIPD) can now be performed for definitive diagnosis of some recessive and X-linked conditions, rather than just paternally inherited dominant and de novo conditions. NIPD/T offers pregnant couples greater choice during their pregnancy as these safer methods avoid the risk of miscarriage associated with invasive testing. As the cost of sequencing falls and technology develops further, there may well be potential for whole exome and whole genome sequencing of the unborn fetus using cell-free DNA in the maternal plasma. How such assays can or should be implemented into the clinical setting remain an area of significant debate, but it is clear that the progress made to date for safer prenatal testing has been welcomed by expectant couples and their healthcare professionals.

Implementing Non-Invasive Prenatal Diagnosis (NIPD) in a National Health Service Laboratory; From Dominant to Recessive Disorders.

Our UK National Health Service regional genetics laboratory offers NIPD for autosomal dominant and de novo conditions (achondroplasia, thanataphoric dysplasia, Apert syndrome), paternal mutation exclusion for cystic fibrosis and a range of bespoke tests. NIPD avoids the risks associated with invasive testing, making prenatal diagnosis more accessible to families at high genetic risk. However, the challenge remains in offering definitive diagnosis for autosomal recessive diseases, which is complicated by the predominance of the maternal mutant allele in the cell-free DNA sample and thus requires a variety of different approaches. Validation and diagnostic implementation for NIPD of congenital adrenal hyperplasia (CAH) is further complicated by presence of a pseudogene that requires a different approach. We have used an assay targeting approximately 6700 heterozygous SNPs around the CAH gene (CYP21A2) to construct the high-risk parental haplotypes and tested this approach in five cases, showing that inheritance of the parental alleles can be correctly identified using NIPD. We are evaluating various measures of the fetal fraction to help determine inheritance of parental mutations. We are currently exploring the utility of an NIPD multi-disorder panel for autosomal recessive disease, to make testing more widely applicable to families with a variety of serious genetic conditions.