Next-generation sequencing of 12 obesity genes in a Portuguese cohort of patients with overweight and obesity

We examined 12 monogenic obesity genes in 72 Portuguese individuals with overweight and obesity (class 1 and class 2), some of which with suspected genetic obesity, to identify known or unknown potential obesity variants. Genomic DNA was analyzed for variants in genes LEP, LEPR, MC4R, POMC, PCSK1, BDNF, NTRK2, SIM1, SH2B1, UCP3, GCG and ADCY3 through next generation sequencing (NGS). The impact of the rare variants was investigated in the ClinVar database and using in silico tools for prediction of pathogenicity. Four potential pathogenic missense variants were detected at the heterozygous state in five individuals: two in the ADCY3 gene, NM_004036.5:c.1153G > A (p.Val385Ile) (rs756783003) and NM_004036.5:c.1222G > A (p.Gly408Arg) (rs201606553), one in gene SH2B1, NM_001145795.1:c.127C > A (p.Arg43Ser) (rs547678855), and the fourth in gene POMC NM_000939.4:c.706C > G (p.Arg236Gly) (rs28932472), which was found in two individuals. Moreover, six rare variants near splicing sites were also identified, as well as eight rare synonymous variants. In summary, some potential pathogenic rare missense variants were identified, two of them in ADCY3 gene, the most recently identified gene as having a role in monogenic obesity. Further analysis should be performed to confirm the clinical relevance of these variants.     

Two Siblings with Homozygous Pathogenic Splice‐Site Variant in Mitochondrial Asparaginyl–tRNA Synthetase (NARS2)

A homozygous missense mutation (c.822G>C) was found in the gene encoding the mitochondrial asparaginyl–tRNA synthetase (NARS2) in two siblings born to consanguineous parents. These siblings presented with different phenotypes: one had mild intellectual disability and epilepsy in childhood, whereas the other had severe myopathy. Biochemical analysis of the oxidative phosphorylation (OXPHOS) complexes in both siblings revealed a combined complex I and IV deficiency in skeletal muscle. In‐gel activity staining after blue native‐polyacrylamide gel electrophoresis confirmed the decreased activity of complex I and IV, and, in addition, showed the presence of complex V subcomplexes. Considering the consanguineous descent, homozygosity mapping and whole‐exome sequencing were combined revealing the presence of one single missense mutation in the shared homozygous region. The c.822G>C variant affects the 3′ splice site of exon 7, leading to skipping of the whole exon 7 and a part of exon 8 in the NARS2 mRNA. In EBV‐transformed lymphoblasts, a specific decrease in the amount of charged mt‐tRNA^Asn was demonstrated as compared with controls. This confirmed the pathogenic nature of the variant. To conclude, the reported variant in NARS2 results in a combined OXPHOS complex deficiency involving complex I and IV, making NARS2 a new member of disease‐associated aaRS2.     

Paediatric survivors beyond infancy with Stüve-Wiedemann syndrome – A case series from the West Midlands,UK

Stüve-Wiedemann Syndrome (STWS) is an autosomal recessive condition caused by variants in the LIFR gene, presenting with respiratory failure, hyperthermia and skeletal dysplasia in the neonatal period. Historically identified as a lethal condition, more children are now managed holistically from early in life with multidisciplinary team involvement with improved outcomes. This stems from early diagnosis, supported by molecular testing in the pre and postnatal periods.This report includes five such cases with survival in childhood to 10 years old in the UK affected by skeletal abnormalities, hyperthermia, respiratory distress and their diagnostic odyssey. All cases have a molecular diagnosis; two patients (family 1) were found to be homozygous for a novel pathogenic LIFR variant NM_002310.5:c.704G > A, p.(Trp235Ter). One patient (family 2) is compound heterozygous with the previously reported LIFR variant NM_002310.5:c.756dup p.(Lys253Ter), and a second novel variant NM_002310.5:c.397+5G > A. Two patients (family 3) are homozygous for one of the same LIFR variants NM_002310.5:c.756dup p.(Lys253Ter) as in family 2.This report discusses genotypic and phenotypic data for five patients with STWS, as well as the need for multi-disciplinary, proactive management and genetic counselling.     

FLVCR1-related disease as a rare cause of retinitis pigmentosa and hereditary sensory autonomic neuropathy

FLVCR1 encodes for a transmembrane heme exporter protein and it is known to cause a rare form of syndromic retinitis pigmentosa: posterior column ataxia with retinitis pigmentosa. Recently, the FLVCR1-associated phenotype has been expanded with sporadic reports of hereditary sensory-autonomic neuropathy or non-syndromic retinitis pigmentosa. Here, we report a 23-year- old female with early onset hypomyelinating sensory-autonomic neuropathy and retinitis pigmentosa. Both features were present since childhood. The patient developed signs of advanced retinitis pigmentosa by the age of 10 years leading to legal blindness after the age of 18. Following candidate gene panel testing, which was negative, whole exome sequencing revealed compound heterozygous pathogenic FLVCR1 variants: NM_014053.3: c.3G > T; p.(Met1?) and NM_014053.3: c.730G > A; p.(Gly244Ser), the latter variant is novel. In this report we highlight the association of retinitis pigmentosa with hypomyelinating sensory-autonomic neuropathy, which could be underdiagnosed due to variable severity. To summarize, the phenotypic heterogeneity of FLVCR1 variants is broad and should include retinitis pigmentosa along with range of neurological features.     

The expanding spectrum of PRPS1-associated phenotypes: three novel mutations segregating with X-linked hearing loss and mild peripheral neuropathy

Next-generation sequencing is currently the technology of choice for gene/mutation discovery in genetically-heterogeneous disorders, such as inherited sensorineural hearing loss (HL). Whole-exome sequencing of a single Italian proband affected by non-syndromic HL identified a novel missense variant within the PRPS1 gene ({"type":"entrez-nucleotide","attrs":{"text":"NM_002764.3","term_id":"164663865","term_text":"NM_002764.3"}}NM_002764.3:c.337G>T (p.A113S)) segregating with post-lingual, bilateral, progressive deafness in the proband''s family. Defects in this gene, encoding the phosphoribosyl pyrophosphate synthetase 1 (PRS-I) enzyme, determine either X-linked syndromic conditions associated with hearing impairment (eg, Arts syndrome and Charcot-Marie-Tooth neuropathy type X-5) or non-syndromic HL (DFNX1). A subsequent screening of the entire PRPS1 gene in 16 unrelated probands from X-linked deaf families led to the discovery of two additional missense variants (c.343A>G (p.M115V) and c.925G>T (p.V309F)) segregating with hearing impairment, and associated with mildly-symptomatic peripheral neuropathy. All three variants result in a marked reduction (>60%) of the PRS-I activity in the patients'' erythrocytes, with c.343A>G (p.M115V) and c.925G>T (p.V309F) affecting more severely the enzyme function. Our data significantly expand the current spectrum of pathogenic variants in PRPS1, confirming that they are associated with a continuum disease spectrum, thus stressing the importance of functional studies and detailed clinical investigations for genotype–phenotype correlation.     

Early Onset Marfan Syndrome with multivalvular insufficiency: Report from a tertiary hospital in Tanzania,and a review of the recurrent c.7606G>A p.0 variant in FBN1

Marfan Syndrome is an autosomal dominant connective tissue disorder caused by mutations in the FBN1 gene. Early Onset Marfan Syndrome is at the severe end of the Marfan syndrome spectrum and is frequently associated with variants in exons 24–32 of the FBN1 gene.To the best of our knowledge, this is the first molecularly confirmed patient from Sub-Saharan Africa with Early Onset Marfan Syndrome who presented with tall stature, arachnodactyly, multivalvular insufficiency and ectopia lentis. Sequencing analysis of FBN1 gene revealed a pathogenic (class 5) heterozygous recurrent variant in exon 61 (c.7606G > A p.0NM_000138.3), which was up to now not associated with rapidly progressive Marfan syndrome with multivalvular insufficiency and congestive cardiac failure. This further supports the notion that the interplay of the given FBN1 mutation, one or more genetic modifiers and epigenetic and environmental factors defines the disease phenotype.     

Genetic studies of multiple consanguineous Pakistani families segregating oculocutaneous albinism identified novel and reported mutations

Oculocutaneous albinism (OCA) is an autosomal‐recessive disorder of a defective melanin pathway. The condition is characterized by hypopigmentation of hair, dermis, and ocular tissue. Genetic studies have reported seven nonsyndromic OCA genes, among which Pakistani OCA families mostly segregate TYR and OCA2 gene mutations. Here in the present study, we investigate the genetic factors of eight consanguineous OCA families from Pakistan. Genetic analysis was performed through single‐nucleotide polymorphism (SNP) genotyping (for homozygosity mapping), whole exome sequencing (for mutation identification), Sanger sequencing (for validation and segregation analysis), and quantitative PCR (qPCR) (for copy number variant [CNV] validation). Genetic mapping in one family identified a novel homozygous deletion mutation of the entire TYRP1 gene, and a novel deletion of exon 19 in the OCA2 gene in two apparently unrelated families. In three further families, we identified homozygous mutations in TYR (NM_000372.4:c.1424G > A; p.Trp475*), NM_000372.4:c.895C > T; p.Arg299Cys), and SLC45A2 (NM_016180:c.1532C > T; p.Ala511Val). For the remaining two families, G and H, compound heterozygous TYR variants NM_000372.4:c.1037‐7T > A, NM_000372.4:c.1255G > A (p.Gly419Arg), and NM_000372.4:c.1255G > A (p.Gly419Arg) and novel variant NM_000372.4:c.248T > G; (p.Val83Gly), respectively, were found. Our study further extends the evidence of TYR and OCA2 as genetic mutation hot spots in Pakistani families. Genetic screening of additional OCA cases may also contribute toward the development of Pakistani specific molecular diagnostic tests, genetic counseling, and personalized healthcare.     

The outcome of targeted NGS screening in patients with syndromic forms of sagittal and pansynostosis - IL11RA is an emerging core-gene for pansynostosis

Here, we have studied the prevalence and spectrum of genetic alterations in syndromic forms of sagittal and pansynostosis. Eighteen patients with sagittal synostosis (isolated or combined with other synostoses, except coronal) or pansynostosis were phenotypically assessed by retrospective analysis of medical records, three-dimensional computed tomography skull reconstructions, and registered photos. Patient DNAs were analyzed using a targeted next-generation sequencing (NGS) panel including 63 craniosynostosis (CS) related genes. Pathogenic and likely pathogenic variants were found in 72% of the cases, mainly affecting FGFR2, TWIST1, IL11RA, and SKI. Two patients that were negative at NGS screening – one with a supernumerary marker chromosome with duplication of 15q25.2q26.3 and one with a pathogenic PHEX variant – were identified using microarray and single gene analysis, respectively. The overall diagnostic rate in the cohort was thus 83%. We identified two novel likely pathogenic variants in FGFR2 (NM_022970.3: c.811_812delGGinsCC, p.Gly271Pro) and TWIST1 (NM_000474.3: c.476T > A, p.Leu159His), and a novel variant of unclear phenotypic significance in RUNX2 (NM_001024630.3: c.340G > A, p.Val114Ile) which could suggest a modulatory effect. Notably, we also identified three new patients with pansynostosis and a Crouzon-like phenotype with IL11RA mutation. Targeted NGS using a broad panel of CS-related genes is a simple and powerful tool for detecting pathogenic mutations in patients with syndromic forms of CS and multiple suture involvement, in particular pansynostosis. Our results provide additional evidence of an association between pansynostosis and IL11RA, an emerging core gene for autosomal recessive CS.     

De novo missense variants in the RAP1B gene identified in two patients with syndromic thrombocytopenia

We present two independent cases of syndromic thrombocytopenia with multiple malformations, microcephaly, learning difficulties, dysmorphism and other features. Exome sequencing identified two novel de novo heterozygous variants in these patients, c.35G>T p.(Gly12Val) and c.178G>C p.(Gly60Arg), in the RAP1B gene (NM_001010942.2). These variants have not been described previously as germline variants, however functional studies in literature strongly suggest a clinical implication of these two activating hot spot positions. We hypothesize that pathogenic missense variants in the RAP1B gene cause congenital syndromic thrombocytopenia with a spectrum of associated malformations and dysmorphism, possibly through a gain of function mechanism.     

Molecular genetic characterization of Congolese patients with oculocutaneous albinism

BackgroundOculocutaneous albinism (OCA) is an autosomal recessive genetic disorder associated with reduced or absent pigmentation in the skin, hair and eyes. OCA type 2 (OCA2) is the most common type in Sub-Saharan Africa, related to a recurrent 2.7 kb intragenic deletion. Genomic data from Congolese patients are lacking. We aimed to describe genetic causes of OCA2 in a cohort of Congolese persons with OCA, and explore possible genotype-phenotype correlations.MethodsA cross sectional study was conducted from January 2015 to December 2017 in Kinshasa, Democratic Republic of Congo (DRC). 165 Congolese unrelated families with non-syndromic OCA, identified through patients' associations, consented to participate to this study. All index cases were tested for the known 2.7 kb deletion involving the exon 7 of the OCA2 gene. Patients heterozygous for the deletion underwent Sanger sequencing of all exons and flanking sequences in the OCA2 gene. Family segregation was performed for candidate pathogenic variants.ResultsThe 2.7 kb deletion in the OCA2 gene was identified in 136/165 (82.4%) index cases, including 113 (68.5%) homozygotes and 23 (13.9%) heterozygotes. Sanger sequencing identified a pathogenic or likely pathogenic variant in the OCA2 gene in 12 out of 23 heterozygotes investigated (52.1%). Segregation analysis allowed us to locate the point mutation on the trans allele in the three patients from whom parental DNA was available.ConclusionThe OCA2 2.7 kb deletion is the major cause of non-syndromic OCA in Congolese patients recruited in this study, confirming results from other Sub-Saharan African populations. Several additional mutations were detected in OCA patient's heterozygote for the deletion, with to date no evidence for a second frequent founder mutation. The confirmation of a single mutation as the major cause will facilitate genetic counselling in this country.     

A splice site and copy number variant responsible for TTC25-related primary ciliary dyskinesia

Primary ciliary dyskinesia (PCD) is a genetically heterogeneous disorder of motile cilia. With few exceptions, PCD is an autosomal recessive condition, and there are over 40 genes associated with the condition. We present a case of a newborn female with clinical features of PCD, specifically the Kartagener syndrome phenotype, due to variants in TTC25. This gene has been previously associated with PCD in three families. Two multi-gene panels performed as a neonate and at two years of age were uninformative. Exome sequencing was performed by the Care4Rare Canada Consortium on a research basis, and an apparent homozygous intronic variant (TTC25:c.1145+1G > A) was identified that was predicted to abolish the canonical splice donor activity of exon 8. The child's mother was a heterozygous carrier of the variant. The paternal sample did not show the splice variant, and homozygosity was observed across the paternal locus. Microarray analysis showed a 50 kb heterozygous deletion spanning the genes TTC25 and CNP. This is the first example of a pathogenic gross deletion in trans with a splice variant, resulting in TTC25-related PCD.     

Sequestosome-1 (SQSTM1) sequence variants in ALS cases in the UK: prevalence and coexistence of SQSTM1 mutations in ALS kindred with PDB

Mutations in the SQSTM1 gene have been reported to be associated with amyotrophic lateral sclerosis (ALS). We sought to determine the frequency of these mutations in a UK familial ALS (FALS) cohort. Sequences of all eight exons of the SQSTM1 gene were analysed in index cases from 61 different FALS kindred lacking known FALS mutations. Six exonic variants c.463G>A, p.(Glu155Lys), c.822G>C, p.(Glu274Asp), c.888G>T, p.(=), c.954C>T, p.(=), c.1038G>A, p.(=) and c.1175C>T, p.(Pro392Leu) were identified in five FALS index cases, three of which were non-synonymous and three were synonymous. One index case harboured three variants (c.822G>C, c.888G>T and c.954C>T), and a second index case harboured two variants (c.822G>C and c.954C>T). Only the p.(Pro392Leu) and p.(Glu155Lys) mutations were predicted to be pathogenic. In one p.(Pro392Leu) kindred, the carrier developed both ALS and Paget''s disease of bone (PDB), and, in the p.(Glu155Lys) kindred, the father of the proband developed PDB. All p.(Pro392Leu) carriers were heterozygous for a previously reported founder haplotype for PDB, where this mutation has an established causal effect. The frequency of the p.(Pro392Leu) mutation in this UK FALS cohort was 2.3% and 0.97% overall including three previously screened FALS cohorts. Our results confirm the presence of the p.(Pro392Leu) SQSTM1 mutation in FALS. This mutation is the most common SQSTM1 mutation found in ALS to date, and a likely pathogenicity is supported by having an established causal role in PDB. The occurrence of the same mutation in ALS and PDB is indicative of a common pathogenic pathway that converges on protein homeostasis.     

Expansion of the phenotypic and mutational spectrum of Carpenter syndrome

Carpenter syndrome 1 (CRPT1) is an acrocephalopolysyndactyly (ACPS) disorder characterized by craniosynostosis, polysyndactyly, obesity, and other malformations. It is caused by mutations in the gene RAB23. We are reporting on two patients from two unrelated consanguineous Egyptian families. Patient 1 presented with an atypical clinical presentation of Carpenter syndrome including overgrowth with advanced bone age, epileptogenic changes on electroencephalogram and autistic features. Patient 2 presented with typical clinical features suggestive of Carpenter syndrome. Therefore, Patient 1 was subjected to whole exome sequencing (WES) to find an explanation for his unusual features and Patient 2 was subjected to Sanger sequencing of the coding exons of theRAB23 gene to confirm the diagnosis. We identified a novel homozygous missense RAB23 variant (NM_001278668:c.T416C:p.Leu139Pro) in Patient 1 and a novel homozygous splicing variant (NM_016277.5:c.398+1G > A) in Patient 2. We suggest that the overgrowth with advanced bone age, electroencephalogram epileptogenic changes, and autistic features seen in Patient 1 are an expansion of the Carpenter phenotype and could be due to the novel missense RAB23 variant. Additionally, the novel identified RAB23 variants in Patient 1 and 2 broaden the spectrum of variants associated with Carpenter syndrome.     

A novel non-sense mutation in TDP2 causes spinocerebellar ataxia autosomal recessive 23 accompanied by bilateral upward gaze; report of a case and review of the literature

Pathogenic mutations in TDP2, encoding tyrosyl DNA phosphodiesterase 2, cause Spinocerebellar Ataxia autosomal recessive 23 (SCAR23). It is a rare autosomal recessive disorder and mainly has been reported in the European population. Thus far, merely eight patients harboring four TDP2 variants have been reported in the literature. In this study, a novel pathogenic variant (NM_016614: c.4G > T, p.Glu2*) was identified by Whole-Exome and confirmed by Sanger sequencing. The proband has both intellectual and developmental delay, dysphasia, elbow contracture, and upward gaze. The elbow contracture has not been previously described in previous SCAR23 cases. Lastly, we briefly review the phenotypic features of the patients with SCAR23 in the literature.     

Mapping the TYR gene reveals novel and previously reported variants in Eastern Indian patients highlighting preponderance of the same changes in multiple unrelated ethnicities

Oculocutaneous albinism (OCA) is a group of congenital autosomal recessive disorders with seven known subtypes (OCA1–OCA7) characterized by loss or absence of pigmentation in the skin, hair, and eyes. OCA1, caused by pathogenic variations in the tyrosinase (TYR) gene, has been documented to be the most prevalent subtype across the world including India. In the present study, we recruited 53 OCA-affected individuals from 45 unrelated families belonging to 20 different marriage groups/ethnicities of 15 different districts of West Bengal. We took a targeted sequencing-based approach to find the causal variations in the TYR gene. We report here identification of two novel potentially pathogenic variations [NM_000372.4:c.614C>T, NP_000363.1:p.(Pro205Leu), and NM_000372.4:c.1036+1=/G>T], one novel synonymous TYR variant [NM_000372.4:c.204=/A>G, NP_000363.1:p.(Gln68=)], two pathogenic variations documented for the first time in Indian OCA cases [NM_000372.4:c.1147G>A, NP_000363.1:p.(Asp383Asn), and NM_000372.4:c.585G>A, NP_000363.1:p.(Trp195*)], along with nine previously reported pathogenic variants in 36 out of 53 (∼68%) patients recruited. We report common haplotype backgrounds for the two most prevalent variations [NM_000372.4:c.124G>A, NM_000372.4:c.832C>T] in cases belonging to different marriage/ethnic groups, suggesting a possible founder effect. To our knowledge, this is the most comprehensive genetic study on OCA1 from India, firmly establishing OCA1 as the commonest form of albinism in this part of the world.     

Caution in interpretation of disease causality for heterozygous loss-of-function variants in the MYH8 gene associated with autosomal dominant disorder

To date, the NM_002472.2(MYH8):c.2021G>A (p.Arg674Gln) missense variant in the MYH8 gene is the only known genetic change in individuals with autosomal dominant trismus-pseudocamptodactyly syndrome with unknown molecular mechanism. Next-generation sequencing (NGS), including targeted gene panels and whole-exome sequencing, is routinely performed in many clinical diagnostic laboratories as standard-of-care testing aimed at identifying disease-causing genomic variants. Whole-exome sequencing has revealed loss-of-function variants in the MYH8 gene. To properly classify the MYH8 loss-of-function variants, we either retrieved them from public databases or retrospectively collected them from individuals genetically tested by custom NGS panels or by whole-exome sequencing and confirmed using Sanger sequencing. We further evaluated the respective clinical presentations of these individuals with the MYH8 loss-of-function variants. Heterozygous loss-of-function variants in the MYH8 gene were detected in 16 individuals without trismus-pseudocamptodactyly syndrome. Four of these 16 individuals had a pathogenic or likely pathogenic variant detected in another gene that could explain their clinical presentation. Moreover, there are ∼100 MYH8 heterozygous protein-truncating and splice site variants in the ExAC database in different populations. Our results, combined with the population data, indicate that loss-of-function variants in the MYH8 gene do not cause autosomal dominant trismus-pseudocamptodactyly syndrome, and the clinical significance of these variants remains unknown at present. This result highlights the importance of considering the molecular mechanism of disease, variants published in the medical literature, and population genomic data for the correct interpretation of loss-of-function variants in genes associated with autosomal dominant diseases.