Bi-allelic LETM1 variants perturb mitochondrial ion homeostasis leading to a clinical spectrum with predominant nervous system involvement.

Leucine zipper-EF-hand containing transmembrane protein 1 (LETM1) encodes an inner mitochondrial membrane protein with an osmoregulatory function controlling mitochondrial volume and ion homeostasis. The putative association of LETM1 with a human disease was initially suggested in Wolf-Hirschhorn syndrome, a disorder that results from de novo monoallelic deletion of chromosome 4p16.3, a region encompassing LETM1. Utilizing exome sequencing and international gene-matching efforts, we have identified 18 affected individuals from 11 unrelated families harboring ultra-rare bi-allelic missense and loss-of-function LETM1 variants and clinical presentations highly suggestive of mitochondrial disease. These manifested as a spectrum of predominantly infantile-onset (14/18, 78%) and variably progressive neurological, metabolic, and dysmorphic symptoms, plus multiple organ dysfunction associated with neurodegeneration. The common features included respiratory chain complex deficiencies (100%), global developmental delay (94%), optic atrophy (83%), sensorineural hearing loss (78%), and cerebellar ataxia (78%) followed by epilepsy (67%), spasticity (53%), and myopathy (50%). Other features included bilateral cataracts (42%), cardiomyopathy (36%), and diabetes (27%). To better understand the pathogenic mechanism of the identified LETM1 variants, we performed biochemical and morphological studies on mitochondrial K+/H+ exchange activity, proteins, and shape in proband-derived fibroblasts and muscles and in Saccharomyces cerevisiae, which is an important model organism for mitochondrial osmotic regulation. Our results demonstrate that bi-allelic LETM1 variants are associated with defective mitochondrial K+ efflux, swollen mitochondrial matrix structures, and loss of important mitochondrial oxidative phosphorylation protein components, thus highlighting the implication of perturbed mitochondrial osmoregulation caused by LETM1 variants in neurological and mitochondrial pathologies.

The clinical and genetic spectrum of inherited glycosylphosphatidylinositol deficiency disorders.

Inherited glycosylphosphatidylinositol deficiency disorders (IGDs) are a group of rare multisystem disorders arising from pathogenic variants in glycosylphosphatidylinositol anchor pathway (GPI-AP) genes. Despite associating 24 of at least 31 GPI-AP genes with human neurogenetic disease, prior reports are limited to single genes without consideration of the GPI-AP as a whole and with limited natural history data. In this multinational retrospective observational study, we systematically analyse the molecular spectrum, phenotypic characteristics and natural history of 83 individuals from 75 unique families with IGDs, including 70 newly reported individuals; the largest single cohort to date. Core clinical features were developmental delay or intellectual disability (DD/ID, 90%), seizures (83%), hypotonia (72%) and motor symptoms (64%). Prognostic and biologically significant neuroimaging features included cerebral atrophy (75%), cerebellar atrophy (60%), callosal anomalies (57%) and symmetric restricted diffusion of the central tegmental tracts (60%). Sixty-one individuals had multisystem involvement including gastrointestinal (66%), cardiac (19%) and renal (14%) anomalies. Though dysmorphic features were appreciated in 82%, no single dysmorphic feature had a prevalence >30%, indicating substantial phenotypic heterogeneity. Follow-up data were available for all individuals, 15 of whom were deceased at the time of writing. Median age at seizure onset was 6 months. Individuals with variants in synthesis stage genes of the GPI-AP exhibited a significantly shorter time to seizure onset than individuals with variants in transamidase and remodelling stage genes of the GPI-AP (P = 0.046). Forty individuals had intractable epilepsy. The majority of individuals experienced delayed or absent speech (95%), motor delay with non-ambulance (64%), and severe-to-profound DD/ID (59%). Individuals with a developmental epileptic encephalopathy (51%) were at greater risk of intractable epilepsy (P = 0.003), non-ambulance (P = 0.035), ongoing enteral feeds (P < 0.001) and cortical visual impairment (P = 0.007). Serial neuroimaging showed progressive cerebral volume loss in 87.5% and progressive cerebellar atrophy in 70.8%, indicating a neurodegenerative process. Genetic analyses identified 93 unique variants (106 total), including 22 novel variants. Exploratory analyses of genotype-phenotype correlations using unsupervised hierarchical clustering identified novel genotypic predictors of clinical phenotype and long-term outcome with meaningful implications for management. In summary, we expand both the mild and severe phenotypic extremities of the IGDs, provide insights into their neurological basis, and vitally, enable meaningful genetic counselling for affected individuals and their families.

Biallelic and monoallelic variants in PLXNA1 are implicated in a novel neurodevelopmental disorder with variable cerebral and eye anomalies.

PURPOSE: To investigate the effect of PLXNA1 variants on the phenotype of patients with autosomal dominant and recessive inheritance patterns and to functionally characterize the zebrafish homologs plxna1a and plxna1b during development. METHODS: We assembled ten patients from seven families with biallelic or de novo PLXNA1 variants. We describe genotype-phenotype correlations, investigated the variants by structural modeling, and used Morpholino knockdown experiments in zebrafish to characterize the embryonic role of plxna1a and plxna1b. RESULTS: Shared phenotypic features among patients include global developmental delay (9/10), brain anomalies (6/10), and eye anomalies (7/10). Notably, seizures were predominantly reported in patients with monoallelic variants. Structural modeling of missense variants in PLXNA1 suggests distortion in the native protein. Our zebrafish studies enforce an embryonic role of plxna1a and plxna1b in the development of the central nervous system and the eye. CONCLUSION: We propose that different biallelic and monoallelic variants in PLXNA1 result in a novel neurodevelopmental syndrome mainly comprising developmental delay, brain, and eye anomalies. We hypothesize that biallelic variants in the extracellular Plexin-A1 domains lead to impaired dimerization or lack of receptor molecules, whereas monoallelic variants in the intracellular Plexin-A1 domains might impair downstream signaling through a dominant-negative effect.

Tay-Sachs Disease: Two Novel Rare HEXA Mutations from Pakistan and Morocco.

BACKGROUND: Tay-Sachs disease (TSD) is a rare autosomalrecessive genetic disorder characterized by progressive destruction of nerve cells in the brain and spinal cord. It is caused by genetic variations in the HEXA gene leading to a deficiency of ß hexosaminidase A (HEXA) isoenzyme activity. This study aimed to identify causative gene variants in 3 unrelated consanguineous families presented with TSD from Pakistan and Morocco. METHODS: Detailed clinical investigations were carried out on probands in 3 unrelated consanguineous families of Pakistani and Moroccan origin. Targeted gene sequencing and Whole Exome Sequencing (WES) were performed for variant identification. Candidate variants were checked for co-segregation with the phenotype using Sanger sequencing. Public databases including ExAC, GnomAD, dbSNP and the 1,000 Genome Project were searched to determine frequencies of the alleles. Conservation of the missense variants was ensured by aligning orthologous protein sequences from diverse vertebrate species. RESULTS: We report on 3 children presented with Tay-Sachs Disease. The ß hexosaminidaseA enzyme activity was reduced in the Pakistani patient in one of the pedigrees. Genetic testing revealed 2 novel homozygous variants (p.Asp386Alafs*13 and p.Trp266Gly) in the gene HEXA in Pakistani and Moroccan patients respectively.The third family of Pakistani origin revealed a previously reported variant (p.Tyr427Ilefs*5) in HEXA. p.Tyr427Ilefs*5 is the most commonly occurring pathogenic variationin Ashkenazi but was not reported in Pakistani population. CONCLUSION: Our study further expands the ethnic and mutational spectrum of Tay-Sachs disease emphasizing the usefulness of WES as a powerful diagnostic tool where enzymatic activity is not performed for Tay-Sachs disease. The study recommends targeted screening for these mutations (p.Tyr427Ilefs5) for cost effective testing of TSD patients. Further, the study would assist in carrier testing and prenatal diagnosis of the affected families.

Diagnostic evaluation of heel prick newborn screening of thyroid stimulating hormone on dissociation-enhanced lanthanide fluorescence immunoassay with the establishment of reference value in Pakistani neonates.

OBJECTIVE: To develop and validate a method on Dissociation Enhanced Lanthanide Fluorescence Immunoassay for neonatal heel prick blood human thyroid stimulating hormone and the establishment of its reference value in the local population. METHODS: The multi-centre cross-sectional validation study was conducted from September 2016 to September 2018 at Zahra Beau Naqvi Foundation Welfare Trust laboratory, Islamabad, Pakistan, and comprised samples related to newborns aged 1 month or less taken from neonatal units of 39 hospitals based in Punjab, Khyber Pakhtunkhuwa, Gilgit-Baltistan and Azad Jammu and Kashmir. Samples were collected after 24 hours of birth using the heel prick test. The samples were dried and sent to the laboratory for assessment where Dissociation Enhanced Lanthanide Fluorescent Immunoassay was used to estimate thyroid stimulating hormone levels. Data recorded included age, gender, and birth detail, like gestational age, mode of delivery etc. Data was analysed using SPSS 21. Method validation and reference value were manually calculated. RESULTS: Of the 14,147 samples received, 8,207(58%) related to boys and 5,940(42%) to girls. Most samples 4903(34.6%) came from Peshawar. The overall mean age of the newborns was 5.6±4.8 days. Thyroid stimulating hormone data was divided into three groups; positive with median value 27.8±36.6 uIU/ml, negative with median 1.42±1.60 uIU/ml, and borderline with median 11.4±4.12uIU/ml. Prevalence of congenital hypothyroidism in high-risk population in the positive group was 39(0.3%), negative 14,012(99.0%) and borderline 96(0.7%). Reference cut-off was calculated as 7.06uIU/ml for screening of healthy and positive cases of congenital hypothyroidism. Method Validation results showed limit of detection -0.5uU/ml, limit of quantitation LOQ 0.8uU/ml, accuracy 100±5%, precision coefficient of variation at each level of calibrators -4, 8.8, 1.2, 11.3, 7.2 and 4.3% respectively, and linearity from to 0.8uU/ml to 254.1uU/ml. CONCLUSIONS: Neonatal human thyroid stimulating hormone by heel prick blood was found to be an affordable and highly sensitive method of screening for congenital hypothyroidism.

Safety and efficacy of laser lithotripsy for complicated biliary stones using direct choledochoscopy.

BACKGROUND: The first-line therapy for choledocholithiasis is endoscopic retrograde cholangiopancreatography (ERCP) with stone extraction, which is successful in over 90% of cases. However, large biliary stones often require extracorporeal shockwave lithotripsy, electrohydraulic lithotripsy (EHL), or laser lithotripsy. The objective of our study was to assess the safety and efficacy of laser lithotripsy with choledochoscopy guidance. METHODS: Between March 2001 and November 2009, laser lithotripsy with a holmium laser was used for complicated bile stones in 20 patients. All patients included had failed standard stone extraction techniques after a mean of 2.1 ± 1.1 ERCP sessions. Main outcome measures included complete stone clearance and complications post-procedure. RESULTS: Twenty patients (mean age 61.0 ± 22.3 years, six men) underwent laser lithotripsy with a mean stone size was 2.2 cm (range 1.1-3.5 cm) and a mean number of stones of 2.2 (range 1-6). A mean of 0.25 ± 0.20 kJ was applied during laser lithotripsy sessions with a mean procedure time of 85.3 ± 23.0 min. The majority (18/20, 90%) achieved final clearance after a mean of 1.4 ± 0.8 (29 total) laser sessions and a mean of 1.9 ± 0.8 (38 total) ERCP sessions. Five complications occurred: two patients required post-procedure admission for pain and three patients had bile leaks. All bile leaks were minor and resolved after biliary stenting. CONCLUSIONS: Laser lithotripsy using the holmium laser is safe and effective with direct cholangioscopic guidance. Further prospective studies are warranted.

Panton-Valentine leukocidin Staphylococcus causing fatal necrotising pneumonia in a young boy.

Panton-Valentine leukocidin (PVL) toxin producing strains of Staphylococcus aureus are known to cause skin and soft tissue infection. They can also cause necrotising pneumonia in otherwise healthy individuals. Here we report a case of severe, necrotising, haemorrhagic pneumonia in a 12-year-old boy who presented with a four-day history of a sore throat and fever. During his admission he deteriorated and needed full ventilatory support but despite all efforts he died. Postmortem examination lung swabs confirmed the presence of PVL-associated S aureus. There is a need to improve awareness of this disease among medical practitioners as early diagnosis and appropriate management can save lives.

Endoscopic retrograde cholangiopancreatography complications in the era of cholangioscopy: is there an increased risk?

BACKGROUND: Single-operator cholangioscopy allows direct visualization of the biliary tree and is being used in the diagnosis and treatment of various biliary conditions. To date, there are few data examining complications of single-operator cholangioscopy. METHODS: We evaluated all endoscopic retrograde cholangiopancreatography procedures over a two-year period and compared its complication rate to single-operator cholangioscopy in a tertiary care centre with extensive experience in single-operator cholangioscopy. A total of 2087 patients (55% men, mean age 57.4±16.4) had a therapeutic endoscopic retrograde cholangiopancreatography, out of which 169 also had single-operator cholangioscopy performed on them. RESULTS: 169 single-operator cholangioscopy procedures were performed (53% men) with a mean patient age of 60.7±15.2 years. Out of the 2087 patients, 160 complications occurred (7.7%), and included pancreatitis (n=47, 2.2%), infection (n=24, 1.1%), bleeding (n=44, 2.1%), perforation (n=16, 0.8%) and other (n=29, 1.4%). Univariate analysis on overall complications identified seven variables with a p value<0.2, which were included in the multivariate analysis. Biliary sphincterotomy, pancreatic duct stent placement, and ampullectomy were associated with increased complications. Single-operator cholangioscopy was not associated with increased complications on multivariate analysis. CONCLUSION: Single-operator cholangioscopy is not associated with an increased rate of complications when compared to endoscopic retrograde cholangiopancreatography. The types and frequencies of overall endoscopic retrograde cholangiopancreatography complications are similar to previously reported series.