Phenotype variability of infantile-onset multisystem neurologic, endocrine, and pancreatic disease IMNEPD

Conserved quality control mechanisms of mitochondrial protein import

Mitochondria carry out essential functions for the cell, including energy production, various biosynthesis pathways, formation of co-factors and cellular signalling in apoptosis and inflammation. The functionality of mitochondria requires the import of about 900-1300 proteins from the cytosol in baker's yeast Saccharomyces cerevisiae and human cells, respectively. The vast majority of these proteins pass the outer membrane in a largely unfolded state through the translocase of the outer mitochondrial membrane (TOM) complex. Subsequently, specific protein translocases sort the precursor proteins into the outer and inner membranes, the intermembrane space and matrix. Premature folding of mitochondrial precursor proteins, defects in the mitochondrial protein translocases or a reduction of the membrane potential across the inner mitochondrial membrane can cause stalling of precursors at the protein import apparatus. Consequently, the translocon is clogged and non-imported precursor proteins accumulate in the cell, which in turn leads to proteotoxic stress and eventually cell death. To prevent such stress situations, quality control mechanisms remove non-imported precursor proteins from the TOM channel. The highly conserved ubiquitin-proteasome system of the cytosol plays a critical role in this process. Thus, the surveillance of protein import via the TOM complex involves the coordinated activity of mitochondria-localized and cytosolic proteins to prevent proteotoxic stress in the cell.

A Novel PTRH2 Gene Mutation Causing Infantile-onset Multisystem Neurologic, Endocrine, and Pancreatic Disease in a Bahraini Patient

Infantile-onset multisystem neurologic, endocrine, and pancreatic disease (IMNEPD) is a rare autosomal recessive multisystemic disease with a prevalence of < 1/1 000 000. The wide spectrum of symptoms and associated diseases makes the diagnosis of this disease particularly challenging. Here, we report a 12-year-old Bahraini male who presented with the core clinical features of IMNEPD including intellectual disability, global developmental delay, sensorineural hearing loss, endocrine dysfunction, and exocrine pancreatic insufficiency. The diagnosis was confirmed by genetic testing using whole exome sequencing. This is the first reported case of IMNEPD from Bahrain and was found to have a novel homozygous peptidyl-tRNA hydrolase 2 (PTRH2) gene mutation (NM_001015509.2: c.370del p.(Glu124Lysfs*4)). Moreover, we conducted an extensive literature review with an emphasis on the variable clinical spectrum and genotypes of previously reported patients in comparison to our case.

PTRH2 is Necessary for Purkinje Cell Differentiation and Survival and its Loss Recapitulates Progressive Cerebellar Atrophy and Ataxia Seen in IMNEPD Patients

Hom ozygous variants in the peptidyl-tRNA hydrolase 2 gene (PTRH2) cause infantile-onset multisystem neurologic, endocrine, and pancreatic disease. The objective is to delineate the mechanisms underlying the core cerebellar phenotype in this disease. For this, we generated constitutive (Ptrh2LoxPxhCMVCre, Ptrh2-/- mice) and Purkinje cell (PC) specific (Ptrh2LoxPxPcp2Cre, Ptrh2ΔPCmice) Ptrh2 mutant mouse models and investigated the effect of the loss of Ptrh2 on cerebellar development. We show that Ptrh2-/- knockout mice had severe postnatal runting and lethality by postnatal day 14. Ptrh2ΔPC PC specific knockout mice survived until adult age; however, they showed progressive cerebellar atrophy and functional cerebellar deficits with abnormal gait and ataxia. PCs of Ptrh2ΔPC mice had reduced cell size and density, stunted dendrites, and lower levels of ribosomal protein S6, a readout of the mammalian target of rapamycin pathway. By adulthood, there was a marked loss of PCs. Thus, we identify a cell autonomous requirement for PTRH2 in PC maturation and survival. Loss of PTRH2 in PCs leads to downregulation of the mTOR pathway and PC atrophy. This suggests a molecular mechanism underlying the ataxia and cerebellar atrophy seen in patients with PTRH2 mutations leading to infantile-onset multisystem neurologic, endocrine, and pancreatic disease.

PTRH2 Gene Variants: Recent Review of the Phenotypic Features and Their Bioinformatics Analysis

Peptidyl-tRNA hydrolase 2 (PTRH2) is an evolutionarily highly conserved mitochondrial protein. The biallelic mutations in the PTRH2 gene have been suggested to cause a rare autosomal recessive disorder characterized by an infantile-onset multisystem neurologic endocrine and pancreatic disease (IMNEPD). Patients with IMNEPD present varying clinical manifestations, including global developmental delay associated with microcephaly, growth retardation, progressive ataxia, distal muscle weakness with ankle contractures, demyelinating sensorimotor neuropathy, sensorineural hearing loss, and abnormalities of thyroid, pancreas, and liver. In the current study, we conducted an extensive literature review with an emphasis on the variable clinical spectrum and genotypes in patients. Additionally, we reported on a new case with a previously documented mutation. A bioinformatics analysis of the various PTRH2 gene variants was also carried out from a structural perspective. It appears that the most common clinical characteristics among all patients include motor delay (92%), neuropathy (90%), distal weakness (86.4%), intellectual disability (84%), hearing impairment (80%), ataxia (79%), and deformity of head and face (~70%). The less common characteristics include hand deformity (64%), cerebellar atrophy/hypoplasia (47%), and pancreatic abnormality (35%), while the least common appear to be diabetes mellitus (~30%), liver abnormality (~22%), and hypothyroidism (16%). Three missense mutations were revealed in the PTRH2 gene, the most common one being Q85P, which was shared by four different Arab communities and was presented in our new case. Moreover, four different nonsense mutations in the PTRH2 gene were detected. It may be concluded that disease severity depends on the PTRH2 gene variant, as most of the clinical features are manifested by nonsense mutations, while only the common features are presented by missense mutations. A bioinformatics analysis of the various PTRH2 gene variants also suggested the mutations to be deleterious, as they seem to disrupt the structural confirmation of the enzyme, leading to loss of stability and functionality.

A Novel Synergistic Association of Variants in PTRH2 and KIF1A Relates to a Syndrome of Hereditary Axonopathy, Outer Hair Cell Dysfunction, Intellectual Disability, Pancreatic Lipomatosis, Diabetes, Cerebellar Atrophy, and Vertebral Artery Hypoplasia

The gene PTRH2 encodes a protein with peptidyl-tRNA hydrolase activity and is involved in the translation process in protein synthesis. The kinesin family member 1-A (KIF1A) gene encodes a molecular motor involved in axonal transport along microtubules. Mutations in these genes lead to respective phenotypical conditions that have been reported in the literature. In this paper, we present a novel syndrome of concurrent occurrence of mutations in the PTRH2 and KIF1A genes in a 19-year-old girl of Dravidian-Tamil descent from the Southern part of India. The girl presented with global developmental delay, intellectual disability, weakness of upper and lower limbs, and diabetes. On workup, she was found to have severe peripheral axonopathy, outer hair cell (OHC) dysfunction, severe bilateral sensorineural hearing loss (SNHL), total pancreatic lipomatosis, exocrine pancreatic insufficiency, cerebellar atrophy, vertebral artery hypoplasia, and scoliosis. The patient had a deceased elder sibling who also had had a similar phenotype. Whole exome sequencing (WES) revealed a novel variant in the PTRH2 gene and a rare variant in the KIF1A gene. The predominant axonal involvement seen in our patient, which was attributable to KIF1A involvement, distinguishes this syndrome from the infantile-onset multisystem neurologic, endocrine, and pancreatic disease (IMNEPD) caused by PTRH2 involvement alone. To the best of our knowledge, this is the first report in the medical literature of a syndrome caused by the synergistic occurrence of mutations in the PTRH2 and KIF1A genes. In order to provide more clarity on the genetic and clinical features of such syndromes and to aid the treating clinician to recognize the existence of such syndromes, we propose the broader umbrella term "neuro-pancreatic syndromes" (NPS). Presently, under NPS, we include two entities: the syndrome described by us in this paper and the IMNEPD. Prompt and effective recognition and management of such NPS would immensely benefit the patient in terms of treatment and prognosis. Furthermore, we hope that this paper will promote further understanding of NPS and foster more research, both clinical and genetic, which would widen the spectrum of NPS. Eventually, this would throw more light on treatment options and ultimately benefit patients with NPS.

Diabetes mellitus in an adolescent girl with intellectual disability caused by novel single base pair duplication in the PTRH2 gene: Expanding the clinical spectrum of IMNEPD

BACKGROUND

Infantile-onset multisystem neurologic, endocrine, and pancreatic disease (IMNEPD) is an extremely rare autosomal recessive disorder with variable expressivity, caused by biallelic mutations in the PTRH2 gene. Core features are global developmental delay or isolated speech delay, intellectual disability, sensorineural hearing loss, ataxia, and pancreatic insufficiency (both exocrine and endocrine). Additional features may include postnatal microcephaly, peripheral neuropathy, facial dysmorphism, and cerebellar atrophy. In literature, there are only a few anecdotal case reports and none of the previous cases presented with diabetic ketoacidosis.

METHODS

We are reporting a 12-year old adolescent girl with mild intellectual disability who presented with fever, pain abdomen for 2 days, and fast breathing for one day.

RESULTS

Her random blood sugar was 472 mg/dl and arterial blood gas revealed high anion gap metabolic acidosis. Urine examination showed ketonuria. On further evaluation, she was found to have demyelinating sensorimotor polyneuropathy and sensorineural hearing loss. Neuroimaging and other ancillary investigations were normal. Whole exome sequencing revealed a novel homozygous single base pair duplication in exon 1 of the PTRH2 gene (c.127dupA, p.Ser43LysfsTer11), confirming the diagnosis of IMNEPD.

CONCLUSIONS

Apart from describing a novel single base pair duplication causing protein truncation in the PTRH2 gene for the first time, our case also expanded the clinical spectrum of IMNEPD, as this is the first case with seemingly pure neurodevelopmental phenotype, who later developed diabetes mellitus, without any exocrine pancreatic abnormality. IMNEPD should be considered in children or adolescents with global developmental delay or intellectual disability when they develop diabetes mellitus.

PTRH2: an adhesion regulated molecular switch at the nexus of life, death, and differentiation

Peptidyl-tRNA hydrolase 2 (PTRH2; Bit-1; Bit1) is an underappreciated regulator of adhesion signals and Bcl2 expression. Its key roles in muscle differentiation and integrin-mediated signaling are central to the pathology of a recently identified patient syndrome caused by a cluster of Ptrh2 gene mutations. These loss-of-function mutations were identified in patients presenting with severe deleterious phenotypes of the skeletal muscle, endocrine, and nervous systems resulting in a syndrome called Infantile-onset Multisystem Nervous, Endocrine, and Pancreatic Disease (IMNEPD). In contrast, in cancer PTRH2 is a potential oncogene that promotes malignancy and metastasis. PTRH2 modulates PI3K/AKT and ERK signaling in addition to Bcl2 expression and thereby regulates key cellular processes in response to adhesion including cell survival, growth, and differentiation. In this Review, we discuss the state of the science on this important cell survival, anoikis and differentiation regulator, and opportunities for further investigation and translation. We begin with a brief overview of the structure, regulation, and subcellular localization of PTRH2. We discuss the cluster of gene mutations thus far identified which cause developmental delays and multisystem disease. We then discuss the role of PTRH2 and adhesion in breast, lung, and esophageal cancers focusing on signaling pathways involved in cell survival, cell growth, and cell differentiation.

Biallelic MADD variants cause a phenotypic spectrum ranging from developmental delay to a multisystem disorder

In pleiotropic diseases, multiple organ systems are affected causing a variety of clinical manifestations. Here, we report a pleiotropic disorder with a unique constellation of neurological, endocrine, exocrine, and haematological findings that is caused by biallelic MADD variants. MADD, the mitogen-activated protein kinase (MAPK) activating death domain protein, regulates various cellular functions, such as vesicle trafficking, activity of the Rab3 and Rab27 small GTPases, tumour necrosis factor-α (TNF-α)-induced signalling and prevention of cell death. Through national collaboration and GeneMatcher, we collected 23 patients with 21 different pathogenic MADD variants identified by next-generation sequencing. We clinically evaluated the series of patients and categorized the phenotypes in two groups. Group 1 consists of 14 patients with severe developmental delay, endo- and exocrine dysfunction, impairment of the sensory and autonomic nervous system, and haematological anomalies. The clinical course during the first years of life can be potentially fatal. The nine patients in Group 2 have a predominant neurological phenotype comprising mild-to-severe developmental delay, hypotonia, speech impairment, and seizures. Analysis of mRNA revealed multiple aberrant MADD transcripts in two patient-derived fibroblast cell lines. Relative quantification of MADD mRNA and protein in fibroblasts of five affected individuals showed a drastic reduction or loss of MADD. We conducted functional tests to determine the impact of the variants on different pathways. Treatment of patient-derived fibroblasts with TNF-α resulted in reduced phosphorylation of the extracellular signal-regulated kinases 1 and 2, enhanced activation of the pro-apoptotic enzymes caspase-3 and -7 and increased apoptosis compared to control cells. We analysed internalization of epidermal growth factor in patient cells and identified a defect in endocytosis of epidermal growth factor. We conclude that MADD deficiency underlies multiple cellular defects that can be attributed to alterations of TNF-α-dependent signalling pathways and defects in vesicular trafficking. Our data highlight the multifaceted role of MADD as a signalling molecule in different organs and reveal its physiological role in regulating the function of the sensory and autonomic nervous system and endo- and exocrine glands.

The Classification of Autosomal Recessive Cerebellar Ataxias: a Consensus Statement from the Society for Research on the Cerebellum and Ataxias Task Force

There is currently no accepted classification of autosomal recessive cerebellar ataxias, a group of disorders characterized by important genetic heterogeneity and complex phenotypes. The objective of this task force was to build a consensus on the classification of autosomal recessive ataxias in order to develop a general approach to a patient presenting with ataxia, organize disorders according to clinical presentation, and define this field of research by identifying common pathogenic molecular mechanisms in these disorders. The work of this task force was based on a previously published systematic scoping review of the literature that identified autosomal recessive disorders characterized primarily by cerebellar motor dysfunction and cerebellar degeneration. The task force regrouped 12 international ataxia experts who decided on general orientation and specific issues. We identified 59 disorders that are classified as primary autosomal recessive cerebellar ataxias. For each of these disorders, we present geographical and ethnical specificities along with distinctive clinical and imagery features. These primary recessive ataxias were organized in a clinical and a pathophysiological classification, and we present a general clinical approach to the patient presenting with ataxia. We also identified a list of 48 complex multisystem disorders that are associated with ataxia and should be included in the differential diagnosis of autosomal recessive ataxias. This classification is the result of a consensus among a panel of international experts, and it promotes a unified understanding of autosomal recessive cerebellar disorders for clinicians and researchers.

Infantile-Onset Multisystem Neurologic, Endocrine, and Pancreatic Disease: Case and Review

We report three brothers born to consanguineous parents of Syrian descent, with a homozygous novel c.324G&gt;A (p.W108*) mutation in PTRH2 that encodes peptidyl-tRNA hydrolase 2, causing infantile-onset multisystem neurologic, endocrine, and pancreatic disease (IMNEPD). We describe the core clinical features of postnatal microcephaly, motor and language delay with regression, ataxia, and hearing loss. Additional features include epileptic seizures, pancreatic insufficiency, and peripheral neuropathy. Clinical phenotyping enabled a targeted approach to the investigation and identification of a novel homozygous nonsense mutation in PTRH2, c.324G&gt;A (p.W108*). We compare our patients with those recently described and review the current literature for IMNEPD.

Genome-wide study to detect single nucleotide polymorphisms associated with visceral and subcutaneous fat deposition in Holstein dairy cows

Excessive abdominal fat might be associated with more severe metabolic disorders in Holstein cows. Our hypothesis was that there are genetic differences between cows with low and high abdominal fat deposition and a normal cover of subcutaneous adipose tissue. The objective of this study was to assess the genetic basis for variation in visceral adiposity in US Holstein cows. The study included adult Holstein cows sampled from a slaughterhouse (Green Bay, WI, USA) during September 2016. Only animals with a body condition score between 2.75 and 3.25 were considered. The extent of omental fat at the level of the insertion of the lesser omentum over the pylorus area was assessed. A group of 100 Holstein cows with an omental fold &lt;5 mm in thickness and minimum fat deposition throughout the entire omentum, and the second group of 100 cows with an omental fold ⩾20 mm in thickness and with a marked fat deposition observed throughout the entire omentum were sampled. A small piece of muscle from the neck was collected from each cow into a sterile container for DNA extraction. Samples were submitted to a commercial laboratory for interrogation of genome-wide genomic variation using the Illumina BovineHD Beadchip. Genome-Wide association analysis was performed to test potential associations between fat deposition and genomic variation. A univariate mixed linear model analysis was performed using genome-wide efficient mixed model association to identify single nucleotide polymorphisms (SNPs) significantly associated with variation in a visceral fat deposition. The chip heritability was 0.686 and the estimated additive genetic and residual variance components were 0.427 and 0.074, respectively. In total, 11 SNPs defining four quantitative trait locus (QTL) regions were found to be significantly associated with visceral fat deposition (P&lt;0.00001). Among them, two of the QTL were detected with four and five significantly associated SNPs, respectively; whereas, the QTLs detected on BTA12 and BTA19 were each detected with only one significantly associated SNP. No enriched gene ontology terms were found within the gene networks harboring these genes when supplied to DAVID using either the Bos taurus or human gene ontology databases. We conclude that excessive omental fat in Holstein cows with similar body condition scores is not caused by a single Mendelian locus and that the trait appears to be at least moderately heritable; consequently, selection to reduce excessive omental fat is potentially possible, but would require the generation of predicted transmitting abilities from larger and random samples of Holstein cattle.

Elsahy-Waters syndrome is caused by biallelic mutations in CDH11

Elsahy-Waters syndrome (EWS), also known as branchial-skeletal-genital syndrome, is a distinct dysmorphology syndrome characterized by facial asymmetry, broad forehead, marked hypertelorism with proptosis, short and broad nose, midface hypoplasia, intellectual disability, and hypospadias. We have recently published a homozygous potential loss of function variant in CDH11 in a boy with a striking resemblance to EWS. More recently, another homozygous truncating variant in CDH11 was reported in two siblings with suspected EWS. Here, we describe in detail the clinical phenotype of the original CDH11-related patient with EWS as well as a previously unreported EWS-affected girl who was also found to have a novel homozygous truncating variant in CDH11, which confirms that EWS is caused by biallelic CDH11 loss of function mutations. Clinical features in the four CDH11 mutation-positive individuals confirm the established core phenotype of EWS. Additionally, we identify upper eyelid coloboma as a new, though infrequent clinical feature. The pathomechanism underlying EWS remains unclear, although the limited phenotypic data on the Cdh11^-/- mouse suggest that this is a potentially helpful model to explore the craniofacial and brain development in EWS-affected individuals.