Lisa Worgan

The p.M292T NDUFS2 mutation causes complex I-deficient Leigh syndrome in multiple families

Isolated complex I deficiency is the most frequently observed oxidative phosphorylation defect in children with mitochondrial disease, leading to a diverse range of clinical presentations, including Leigh syndrome. For most patients the genetic cause of the biochemical defect remains unknown due to incomplete understanding of the complex I assembly process. Nonetheless, a plethora of pathogenic mutations have been described to date in the seven mitochondrial-encoded subunits of complex I as well as in 12 of the nuclear-encoded subunits and in six assembly factors. Whilst several mitochondrial DNA mutations are recurrent, the majority of these mutations are reported in single families. We have sequenced core structural and functional nuclear-encoded subunits of complex I in a cohort of 34 paediatric patients with isolated complex I deficiency, identifying pathogenic mutations in 6 patients. These included a novel homozygous NDUFS1 mutation in an Asian child with Leigh syndrome, a previously identified NDUFS8 mutation (c.236C>T, p.P79L) in a second Asian child with Leigh-like syndrome and six novel, compound heterozygous NDUFS2 mutations in four white Caucasian patients with Leigh or Leigh-like syndrome. Three of these children harboured an identical NDUFS2 mutation (c.875T>C, p.M292T), which was also identified in conjunction with a novel NDUFS2 splice site mutation (c.866+4A>G) in a fourth Caucasian child who presented to a different diagnostic centre, with microsatellite and single nucleotide polymorphism analyses indicating that this was due to an ancient common founder event. Our results confirm that NDUFS2 is a mutational hotspot in Caucasian children with isolated complex I deficiency and recommend the routine diagnostic investigation of this gene in patients with Leigh or Leigh-like phenotypes.

Phenotypic expansion and further characterisation of the 17q21.31 microdeletion syndrome

Background: The recognition of the 17q21.31 microdeletion syndrome has been facilitated by high resolution microarray technology. Recent clinical delineation of this condition emphasises a typical facial appearance, cardiac and renal defects, and speech delay in addition to intellectual disability, hypotonia and seizures. Methods and results: We describe 11 previously unreported patients expanding the phenotypic spectrum to include aortic root dilatation, recurrent joint subluxation, conductive hearing loss due to chronic otitis media, dental anomalies, and persistence of fetal fingertip pads. Molecular analysis of the deletions demonstrates a critical region spanning 440 kb involving either partially or wholly five genes, CRHR1, IMP5, MAPT, STH, and KIAA1267. Conclusion: These data have significant implications for the clinical diagnosis and management of other individuals with 17q21.31 deletions.

PIK3CA-associated developmental disorders exhibit distinct classes of mutations with variable expression and tissue distribution

Mosaicism is increasingly recognized as a cause of developmental disorders with the advent of next-generation sequencing (NGS). Mosaic mutations of PIK3CA have been associated with the widest spectrum of phenotypes associated with overgrowth and vascular malformations. We performed targeted NGS using 2 independent deep-coverage methods that utilize molecular inversion probes and amplicon sequencing in a cohort of 241 samples from 181 individuals with brain and/or body overgrowth. We identified PIK3CA mutations in 60 individuals. Several other individuals (n = 12) were identified separately to have mutations in PIK3CA by clinical targeted-panel testing (n = 6), whole-exome sequencing (n = 5), or Sanger sequencing (n = 1). Based on the clinical and molecular features, this cohort segregated into three distinct groups: (a) severe focal overgrowth due to low-level but highly activating (hotspot) mutations, (b) predominantly brain overgrowth and less severe somatic overgrowth due to less-activating mutations, and (c) intermediate phenotypes (capillary malformations with overgrowth) with intermediately activating mutations. Sixteen of 29 PIK3CA mutations were novel. We also identified constitutional PIK3CA mutations in 10 patients. Our molecular data, combined with review of the literature, show that PIK3CA-related overgrowth disorders comprise a discontinuous spectrum of disorders that correlate with the severity and distribution of mutations.

Genotype and clinical care correlations in craniosynostosis: Findings from a cohort of 630 Australian and New Zealand patients

Craniosynostosis is one of the most common craniofacial disorders encountered in clinical genetics practice, with an overall incidence of 1 in 2,500. Between 30% and 70% of syndromic craniosynostoses are caused by mutations in hotspots in the fibroblast growth factor receptor (FGFR) genes or in the TWIST1 gene with the difference in detection rates likely to be related to different study populations within craniofacial centers. Here we present results from molecular testing of an Australia and New Zealand cohort of 630 individuals with a diagnosis of craniosynostosis. Data were obtained by Sanger sequencing of FGFR1, FGFR2, and FGFR3 hotspot exons and the TWIST1 gene, as well as copy number detection of TWIST1. Of the 630 probands, there were 231 who had one of 80 distinct mutations (36%). Among the 80 mutations, 17 novel sequence variants were detected in three of the four genes screened. In addition to the proband cohort there were 96 individuals who underwent predictive or prenatal testing as part of family studies. Dysmorphic features consistent with the known FGFR1‐3/TWIST1‐associated syndromes were predictive for mutation detection. We also show a statistically significant association between splice site mutations in FGFR2 and a clinical diagnosis of Pfeiffer syndrome, more severe clinical phenotypes associated with FGFR2 exon 10 versus exon 8 mutations, and more frequent surgical procedures in the presence of a pathogenic mutation. Targeting gene hot spot areas for mutation analysis is a useful strategy to maximize the success of molecular diagnosis for individuals with craniosynostosis.

MKS1 regulates ciliary INPP5E levels in Joubert syndrome

Background Joubert syndrome (JS) is a recessive ciliopathy characterised by a distinctive brain malformation ‘the molar tooth sign’. Mutations in >27 genes cause JS, and mutations in 12 of these genes also cause Meckel-Gruber syndrome (MKS). The goals of this work are to describe the clinical features of MKS1-related JS and determine whether disease causing MKS1 mutations affect cellular phenotypes such as cilium number, length and protein content as potential mechanisms underlying JS. Methods We measured cilium number, length and protein content (ARL13B and INPP5E) by immunofluorescence in fibroblasts from individuals with MKS1-related JS and in a three-dimensional (3D) spheroid rescue assay to test the effects of disease-related MKS1 mutations. Results We report MKS1 mutations (eight of them previously unreported) in nine individuals with JS. A minority of the individuals with MKS1-related JS have MKS features. In contrast to the truncating mutations associated with MKS, all of the individuals with MKS1-related JS carry ≥1 non-truncating mutation. Fibroblasts from individuals with MKS1-related JS make normal or fewer cilia than control fibroblasts, their cilia are more variable in length than controls, and show decreased ciliary ARL13B and INPP5E. Additionally, MKS1 mutant alleles have similar effects in 3D spheroids. Conclusions MKS1 functions in the transition zone at the base of the cilium to regulate ciliary INPP5E content, through an ARL13B-dependent mechanism. Mutations in INPP5E also cause JS, so our findings in patient fibroblasts support the notion that loss of INPP5E function, due to either mutation or mislocalisation, is a key mechanism underlying JS, downstream of MKS1 and ARL13B.

Beyond the panel: preconception screening in consanguineous couples using the TruSight One “clinical exome”

PurposeTo provide proof of concept by broadening preconception screening beyond targeted testing to inform reproductive risk in consanguineous couples.MethodsConsanguineous couples were screened for autosomal recessive and X-linked disorders using the TruSight One panel of 4,813 genes associated with human disease.ResultsWe recruited 22 couples, of whom 15 elected to have sequencing. We found four couples to be at risk of autosomal recessive disorders, including one with a child affected by Poretti–Boltshauser syndrome (a diagnosis not made prior to the study) and another previously known to carry a β-globin variant. Two couples were found to carry variants unrelated to known family history. These variants were in the genes C5orf42 (associated with Joubert syndrome and orofaciodigital syndrome) and GYS2 (associated with glycogen synthase deficiency). One known variant was not detected—a single exon deletion in FAM20C. We would not expect to identify this variant with the methodology employed. Of the four variants identified, only the β-globin variant would have been found using available commercial preconception screening panels.ConclusionPreconception screening of consanguineous couples for recessive and X-linked disorders using genomic sequencing is practicable, and is likely to detect many more at-risk couples than any targeted panel could achieve. A couples-based approach greatly reduces the associated analysis and counselling burden.

Whole-exome sequencing reanalysis at 12 months boosts diagnosis and is cost-effective when applied early in Mendelian disorders

PurposeWhole-exome sequencing (WES) has revolutionized Mendelian diagnostics, however, there is no consensus on the timing of data review in undiagnosed individuals and only preliminary data on the cost-effectiveness of this technology. We aimed to assess the utility of WES data reanalysis for diagnosis in Mendelian disorders and to analyze the cost-effectiveness of this technology compared with a traditional diagnostic pathway.MethodsWES was applied to a cohort of 54 patients from 37 families with a variety of Mendelian disorders to identify the genetic etiology. Reanalysis was performed after 12 months with an improved WES diagnostic pipeline. A comparison was made between costs of a modeled WES pathway and a traditional diagnostic pathway in a cohort with intellectual disability (ID).ResultsReanalysis of WES data at 12 months improved diagnostic success from 30 to 41% due to interim publication of disease genes, expanded phenotype data from referrer, and an improved bioinformatics pipeline. Cost analysis on the ID cohort showed average cost savings of US

User Acceptability of Whole Exome Reproductive Carrier Testing for Consanguineous Couples in Australia

586 (AU

A novel mutation in GMPPA in siblings with apparent intellectual disability, epilepsy, dysmorphism, and autonomic dysfunction

782) for each additional diagnosis.ConclusionEarly application of WES in Mendelian disorders is cost-effective and reanalysis of an undiagnosed individual at a 12-month time point increases total diagnoses by 11%.

Recessive inactivating mutations in TBCK, encoding a Rab GTPase-activating protein that modulates mTOR signaling, cause severe infantile syndromic encephalopathy

The study aimed to explore with consanguineous couples in Australia the acceptability and perceived utility of whole exome reproductive carrier screening for autosomal recessive and X-linked recessive conditions. Semi-structured interviews with 21 consanguineous couples were conducted prior to the offer of screening. Interviews were coded, and thematic analysis was informed by an inductive approach. Three major themes were identified: experiences and attitudes of Australian consanguineous couples, childhood genetic conditions and beliefs, and the perceived utility of genomic screening. All but one couple had previously sought genetic advice, and a large majority of couples were aware of childhood conditions within their family or community. Thirteen couples perceived consanguinity as increasing the risk of having affected children. Nine spoke of premarital screening programs routinely conducted in their countries of origin. All supported the concept and availability of genomic reproductive carrier screening. Hypothetically, if found to be carriers of a severe childhood disorder, 13 couples reported they would test a pregnancy, and 12 of whom would consider termination of pregnancy or pre-implantation genetic diagnosis. Four couples would not test a pregnancy and two were unsure. A majority of couples would communicate potential at-risk status to family members, although there were some caveats. Fourteen couples chose to have exome screening and reported that they would utilize the results with the goal of preventing childhood conditions. Of these couples, nine (64%) had an affected child but were aware that testing may reveal they were at risk for a child with a different condition and five (71%) without an affected child. While from diverse ethnic and backgrounds, all couples practiced a religion and all but one couple were recruited from the same clinical genetics unit, with a likely higher genetic literacy and bias towards accepting genetic testing. However, the choice made by all couples was reportedly made with consideration of their personal values, their current family situation, and exome testing issues, including fear of incidental findings and concerns about test reliability.The study aimed to explore with consanguineous couples in Australia the acceptability and perceived utility of whole exome reproductive carrier screening for autosomal recessive and X-linked recessive conditions. Semi-structured interviews with 21 consanguineous couples were conducted prior to the offer of screening. Interviews were coded, and thematic analysis was informed by an inductive approach. Three major themes were identified: experiences and attitudes of Australian consanguineous couples, childhood genetic conditions and beliefs, and the perceived utility of genomic screening. All but one couple had previously sought genetic advice, and a large majority of couples were aware of childhood conditions within their family or community. Thirteen couples perceived consanguinity as increasing the risk of having affected children. Nine spoke of premarital screening programs routinely conducted in their countries of origin. All supported the concept and availability of genomic reproductive carrier screening. Hypothetically, if found to be carriers of a severe childhood disorder, 13 couples reported they would test a pregnancy, and 12 of whom would consider termination of pregnancy or pre-implantation genetic diagnosis. Four couples would not test a pregnancy and two were unsure. A majority of couples would communicate potential at-risk status to family members, although there were some caveats. Fourteen couples chose to have exome screening and reported that they would utilize the results with the goal of preventing childhood conditions. Of these couples, nine (64%) had an affected child but were aware that testing may reveal they were at risk for a child with a different condition and five (71%) without an affected child. While from diverse ethnic and backgrounds, all couples practiced a religion and all but one couple were recruited from the same clinical genetics unit, with a likely higher genetic literacy and bias towards accepting genetic testing. However, the choice made by all couples was reportedly made with consideration of their personal values, their current family situation, and exome testing issues, including fear of incidental findings and concerns about test reliability.