Validity and reliability of the MetabQoL 1.0 and assessment of neuropsychiatric burden in organic acidemias: Reflections from Turkey.

OBJECTIVES: The MetabQoL 1.0 is the first disease-specific health related quality of life (HrQoL) questionnaire for patients with intoxication-type inherited metabolic disorders. Our aim was to assess the validity and reliability of the MetabQoL 1.0, and to investigate neuropsychiatric burden in our patient population. METHODS: Data from 29 patients followed at a single center, aged between 8 and 18 years with the diagnosis of methylmalonic acidemia (MMA), propionic acidemia (PA) or isovaleric acidemia (IVA), and their parents were included. The Pediatric Quality of Life Inventory (PedsQoL) was used to evaluate the validity and reliability of MetabQoL 1.0. RESULTS: The MetabQoL 1.0 was shown to be valid and reliable (Cronbach's alpha: 0.64-0.9). Fourteen out of the 22 patients (63.6%) formally evaluated had neurological findings. Of note, 17 out of 20 patients (85%) had a psychiatric disorder when evaluated formally by a child and adolescent psychiatrist. The median mental scores of the MetabQoL 1.0 proxy report were significantly higher than those of the self report (p = 0.023). Patients with neonatal-onset disease had higher MetabQoL 1.0 proxy physical (p = 0.008), mental (p = 0.042), total scores (p = 0.022); and self report social (p = 0.007) and total scores (p = 0.043) than those with later onset disease. CONCLUSIONS: This study continues to prove that the MetabQoL 1.0 is an effective tool to measure what matters in intoxication-type inherited metabolic disorders. Our results highlight the importance of clinical assessment complemented by patient reported outcomes which further expands the evaluation toolbox of inherited metabolic diseases.

Delineation of ADPRHL2 Variants: Report of Two New Patients with Review of the Literature.

ADPRHL2 is involved in posttranslational modification and is known to have a role in physiological functions such as cell signaling, DNA repair, gene control, cell death, and response to stress. Recently, a group of neurological disorders due to ADPRHL2 variants is described, characterized by childhood-onset, stress-induced variable movement disorders, neuropathy, seizures, and neurodegenerative course. We present the diagnostic pathway of two pediatric patients with episodic dystonia and ataxia, who later had a neurodegenerative course complicated by central hypoventilation syndrome due to the same homozygous ADPRHL2 variant. We conducted a systematic literature search and data extraction procedure following the Preferred Reporting Items for Systematic Review and Meta-Analysis 2020 statement in terms of patients with ADPRHL2 variants, from 2018 up to 3 February, 2023. In total, 12 articles describing 47 patients were included in the final analysis. Median age at symptom onset was 2 (0.7-25) years, with the most common presenting symptoms being gait problems (n = 19, 40.4%), seizures (n = 16, 34%), ataxia (n = 13, 27.6%), and weakness (n = 10, 21.2%). Triggering factors (28/47; 59.5%) and regression (28/43; 60.4%), axonal polyneuropathy (9/23; 39.1%), and cerebral and cerebellar atrophy with white matter changes (28/36; 77.7%) were the other clues. The fatality rate and median age of death were 44.6% (n = 21) and 7 (2-34) years, respectively. ADPRHL2 variants should be considered in the context of episodic, stress-induced pediatric and adult-onset movement disorders and seizures.

Impact of Spinal Surgery on Intrathecal Nusinersen Injections in Pediatric Spinal Muscular Atrophy.

BACKGROUND: Complex spinal deformities necessitate surgical interventions that may intervene with intrathecal injections in patients with spinal muscular atrophy (SMA). This study aimed to determine the effect of spinal deformity correction surgery on nusinersen administration. METHODS: Pediatric patients with SMA, operated by a single surgeon, either via magnetically controlled growing rod (MCGR) or definitive fusion (DF) with skip instrumentation, were evaluated retrospectively in terms of safety and feasibility of intrathecal injections. Patients' and their parents' perspectives were evaluated through a questionnaire regarding any shift in the setting of injections. RESULTS: Fourteen patients with 15 spinal surgeries (10 MCGR and 5 DF) were included. Eleven patients received intrathecal treatment both before and after the surgery. Preoperative (n=3) and postoperative (n=9) fluoroscopic guidance was required leading to a shift in the application settings in 6 patients. Of 106 preoperative injections, 15% required fluoroscopy and 2% required anesthesia. Postoperatively, of 88 injections, 73% required fluoroscopy and 26% required anesthesia. No patients discontinued intrathecal injections due to technical difficulties associated with the spinal surgery. CONCLUSIONS: This study demonstrates that spinal surgery does not prevent safe and successful intrathecal nusinersen injections. In the DF group, the skip instrumentation technique provided access to interlaminal space for intrathecal injections. In either surgical group, no further auxillary approach was required. Modifications in the injection technique require an institutional approach, and concerns of patients and their families should be addressed accordingly. LEVEL OF EVIDENCE: IV.

Predictors of Clinically Important Neuroimaging Findings in Children Presenting Pediatric Emergency Department.

OBJECTIVE: The aim of the study is to evaluate predictors of clinically important neuroimaging results, that is, computed tomography and magnetic resonance imaging in children in an academic pediatric emergency department (PED) from 2015 to 2019. METHODS: This study was conducted in an academic PED. The patient's demographic and clinical characteristics of PED visits and neuroimaging findings requested at the PED were recorded for January 1, 2015, to December 31, 2019. In addition, descriptive statistics and logistic regression analyses were conducted. We described and determined the predictors of clinically important neuroimaging findings in children. RESULTS: Clinically important neuroimaging findings were detected in patients with blurred vision ( P = 0.001), ataxia ( P = 0.003), unilateral weakness ( P = 0.004), and altered level of consciousness ( P = 0.026). Clinically important neuroimaging was found 9.4 times higher in patients with altered level of consciousness, 7.4 times higher in patients with focal weakness, 4.6 times higher in patients with blurred vision, and 3.5 times more in patients presenting with ataxia. CONCLUSIONS: Advanced neuroimaging, especially for selected patients in PED, can improve the quality of health care for patients. On the other hand, irrelevant neuroimaging findings can lead physicians away from prompt diagnosis and accurate management. According to our study, advanced neuroimaging can be performed in the early period for both diagnosis and early treatment, especially in selected patients with ataxia, blurred vision, altered consciousness, and unilateral weakness. In other cases, clinicians may find more supporting evidence.

Proteomic Investigation of Differential Interactomes of Glypican 1 and a Putative Disease-Modifying Variant of Ataxia.

In a currently 13-year-old girl of consanguineous Turkish parents, who developed unsteady gait and polyneuropathy at the ages of 3 and 6 years, respectively, we performed whole genome sequencing and identified a biallelic missense variant c.424C>T, p.R142W in glypican 1 (GPC1) as a putative disease-associated variant. Up to date, GPC1 has not been associated with a neuromuscular disorder, and we hypothesized that this variant, predicted as deleterious, may be causative for the disease. Using mass spectrometry-based proteomics, we investigated the interactome of GPC1 WT and the missense variant. We identified 198 proteins interacting with GPC1, of which 16 were altered for the missense variant. This included CANX as well as vacuolar ATPase (V-ATPase) and the mammalian target of rapamycin complex 1 (mTORC1) complex members, whose dysregulation could have a potential impact on disease severity in the patient. Importantly, these proteins are novel interaction partners of GPC1. At 10.5 years, the patient developed dilated cardiomyopathy and kyphoscoliosis, and Friedreich's ataxia (FRDA) was suspected. Given the unusually severe phenotype in a patient with FRDA carrying only 104 biallelic GAA repeat expansions in FXN, we currently speculate that disturbed GPC1 function may have exacerbated the disease phenotype. LC-MS/MS data are accessible in the ProteomeXchange Consortium (PXD040023).

New-Onset Ocular Myasthenia after Multisystem Inflammatory Syndrome in Children.

Neurologic complications have been associated with multisystem inflammatory syndrome in children, possibly involving autoimmune mechanisms. Here, we report a 6-year-old girl who developed myasthenia 11 weeks after severe acute respiratory syndrome coronavirus 2 infection and 8 weeks after the onset of severe multisystem inflammatory syndrome in children.

Evaluation of changes in physician behavior after introduction of pediatric syncope approach protocol in the emergency department.

OBJECTIVES: Syncope is a common presenting symptom in the pediatric emergency department (PED). The etiology of pediatric syncope is generally benign. However, differentiating cardiac and other serious causes from benign causes of syncope are crucial. The aim of this study was to evaluate the change of physicians' behavior after introduction of an institutional protocol designed to act as a guide in the assessment and management of syncope patients in the PED. METHODS: This was a retrospective study, conducted at the PED of our University Children's Hospital. A "pediatric syncope approach protocol" was introduced on March 1, 2019 for quality improvement purposes. Documented information in the medical records, laboratory investigations and the patients' final diagnoses during the six-month periods before and after the protocol introduction were compared. RESULTS: 268 patients were included in the study (131 pre-protocol, 137 post-protocol patients). When compared with the pre-protocol group, there was a significant improvement in the documentation of syncope characteristics (prodromal findings, predisposing factors, association with exercise), cardiac, neurological and electrocardiographic (ECG) warning signs and ordering of cardiac markers in the post-protocol group. CONCLUSIONS: The introduction of the syncope approach protocol in PED has enabled an evidence-based and systematic evaluation and management of syncope patients, and reduced the rates of low-yield investigations. Sustained implementation of this protocol can have long-term benefits in the care of children with syncope at the emergency department.

Further expanding the mutational spectrum of brain abnormalities, neurodegeneration, and dysosteosclerosis: A rare disorder with neurologic regression and skeletal features.

Colony stimulating factor 1 receptor (CSF1R, MIM# 164770) encodes a tyrosine-kinase receptor playing an important role in development of osteoclasts and microglia. Heterozygous CSF1R variants have been known to cause hereditary diffuse leukoencephalopathy with spheroids (HDLS, MIM# 221820), an adult-onset leukoencephalopathy characterized by loss of motor functions and cognitive decline. Recently, a new phenotype characterized by brain abnormalities, neurodegeneration, and dysosteosclerosis (BANDDOS) with biallelic CSF1R pathogenic variants in the etiology has been described. BANDDOS differs from HDLS by early-onset neurodegenerative changes with additional structural brain abnormalities and skeletal findings resembling dysosteosclerosis (DOS). Described skeletal findings of the disease are highly variable ranging from absence of a skeletal phenotype and milder Pyle disease-like to osteopetrosis and DOS. To date, only a few patients carrying biallelic CSF1R variants have been reported. In this clinical report, we describe three siblings with variable skeletal findings along with neurological symptoms ranging from mild to severe in whom exome sequencing revealed a novel homozygous splice site variant in canonical splice donor site of intron 21 adjacent to an exon, which encoding part of kinase domain of CSF1R along with a review of the literature.

Guidelines for the diagnosis and management of methylmalonic acidaemia and propionic acidaemia: First revision.

Isolated methylmalonic acidaemia (MMA) and propionic acidaemia (PA) are rare inherited metabolic diseases. Six years ago, a detailed evaluation of the available evidence on diagnosis and management of these disorders has been published for the first time. The article received considerable attention, illustrating the importance of an expert panel to evaluate and compile recommendations to guide rare disease patient care. Since that time, a growing body of evidence on transplant outcomes in MMA and PA patients and use of precursor free amino acid mixtures allows for updates of the guidelines. In this article, we aim to incorporate this newly published knowledge and provide a revised version of the guidelines. The analysis was performed by a panel of multidisciplinary health care experts, who followed an updated guideline development methodology (GRADE). Hence, the full body of evidence up until autumn 2019 was re-evaluated, analysed and graded. As a result, 21 updated recommendations were compiled in a more concise paper with a focus on the existing evidence to enable well-informed decisions in the context of MMA and PA patient care.

Validation of the EULAR/ACR 2017 idiopathic inflammatory myopathy classification criteria in juvenile dermatomyositis patients.

OBJECTIVES: In 2017, a new set of criteria was proposed by EULAR/ACR to classify idiopathic inflammatory myopathies. Our aim was to validate the EULAR/ACR 2017 classification criteria in juvenile dermatomyositis (JDM) patients. METHODS: This study was carried out at Hacettepe University Children's Hospital Department of Paediatrics, Divisions of Rheumatology, Neurology and Paediatric Pathology Unit. Control patients included inborn errors of metabolism presenting with myopathy and/or rhabdomyolysis, idiopathic rhabdomyolysis, dystrophinopathies, neuromyotonia and systemic rheumatic disorders. Patients' data were collected retrospectively from patient files. RESULTS: Fifty-eight JDM patients (60.3% female) and 40 controls (32.5% female) were included in this study. When the probability cut-off was set at 55% as recommended, the sensitivity/specificity of the new criteria to diagnose JDM were 96.5%/85% in the total cohort, 95.8%/84.6% without the muscle biopsy data and 97%/85.7% with biopsy data. With the ROC curve analysis, the optimal probability cut-off for the whole cohort was found to be >62%; providing a sensitivity/specificity of 96.6% (95% CI: 88.1% to 99.6)/90% (95% CI: 76.3% to 97.2%), and >68.5% for the patients with muscle biopsy providing sensitivity/specificity of 97% (84.7-99.9%)/100% (76.8-100%), respectively. The new EULAR/ACR criteria were the most sensitive, however, the least specific compared to the Tanimoto criteria (sensitivity/specificity 64%/97.5%) and Bohan-Peter criteria (sensitivity/ specificity 74.1%/92.5%). CONCLUSIONS: The new EULAR/ACR criteria performed favourably in our JDM cohort especially with the probability cut-off of >62%.

Inflammatory milieu of muscle biopsies in juvenile dermatomyositis.

Juvenile dermatomyositis (JDM) is an inflammatory myopathy which causes severe morbidity and high mortality if untreated. In this study, we aimed to define the T-helper cell profile in the muscle biopsies of JDM patients. Muscle biopsies of twenty-six patients (50% female) were included in the study. Immunohistochemical expression of CD3, CD20, CD138, CD68, IL-17, Foxp3, IFN-É£, IFN-alpha and IL-4 was studied and muscle biopsies were scored using the JDM muscle biopsy scoring tool. Inflammatory cells were in small clusters in perimysium and perivascular area or scattered throughout the endomysium in most biopsies; however in 2 biopsies, lymphoid follicle-like big clusters were observed, and in one, there was a very dense and diffuse inflammatory infiltration nearly destroying all the muscle architecture. Seventy-three per cent of the biopsies had T cells, 88% had B cells, 57% had plasma cells, and all had macrophages. As for T-helper cell subtypes, 80% of the biopsies were Th1 positive, 92% Th17 positive and 30% Treg positive. No IL-4 positive inflammatory cell was detected, and only 2 biopsies showed IFN-alpha positivity. The mean JDM biopsy score was 17.6, meaning moderate to severe muscular involvement. Visual analogue score of the pathologist was strongly correlated with histopathological features. B cells, macrophages, plasma cells and T cells constitute the inflammatory milieu of the JDM muscle biopsies. As for T cells, JDM is a disease mainly related with Th1 and Th17 T-helper cell subtypes and to some extend Treg. Th2 cells are not involved in the pathogenesis.

Bi-allelic mutations in MYL1 cause a severe congenital myopathy.

Congenital myopathies are typically characterised by early onset hypotonia, weakness and hallmark features on biopsy. Despite the rapid pace of gene discovery, ∼50% of patients with a congenital myopathy remain without a genetic diagnosis following screening of known disease genes. We performed exome sequencing on two consanguineous probands diagnosed with a congenital myopathy and muscle biopsy showing selective atrophy/hypotrophy or absence of type II myofibres. We identified variants in the gene (MYL1) encoding the skeletal muscle fast-twitch specific myosin essential light chain (ELC) in both probands. A homozygous essential splice acceptor variant (c.479-2A > G, predicted to result in skipping of exon 5 was identified in Proband 1, and a homozygous missense substitution (c.488T>G, p.(Met163Arg)) was identified in Proband 2. Protein modelling of the p.(Met163Arg) substitution predicted it might impede intermolecular interactions that facilitate binding to the IQ domain of myosin heavy chain, thus likely impacting on the structure and functioning of the myosin motor. MYL1 was markedly reduced in skeletal muscle from both probands, suggesting that the missense substitution likely results in an unstable protein. Knock down of myl1 in zebrafish resulted in abnormal morphology, disrupted muscle structure and impaired touch-evoked escape responses, thus confirming that skeletal muscle fast-twitch specific myosin ELC is critical for myofibre development and function. Our data implicate MYL1 as a crucial protein for adequate skeletal muscle function and that MYL1 deficiency is associated with severe congenital myopathy.

Correction: The genomic and clinical landscape of fetal akinesia.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The genomic and clinical landscape of fetal akinesia.

PURPOSE: Fetal akinesia has multiple clinical subtypes with over 160 gene associations, but the genetic etiology is not yet completely understood. METHODS: In this study, 51 patients from 47 unrelated families were analyzed using next-generation sequencing (NGS) techniques aiming to decipher the genomic landscape of fetal akinesia (FA). RESULTS: We have identified likely pathogenic gene variants in 37 cases and report 41 novel variants. Additionally, we report putative pathogenic variants in eight cases including nine novel variants. Our work identified 14 novel disease-gene associations for fetal akinesia: ADSSL1, ASAH1, ASPM, ATP2B3, EARS2, FBLN1, PRG4, PRICKLE1, ROR2, SETBP1, SCN5A, SCN8A, and ZEB2. Furthermore, a sibling pair harbored a homozygous copy-number variant in TNNT1, an ultrarare congenital myopathy gene that has been linked to arthrogryposis via Gene Ontology analysis. CONCLUSION: Our analysis indicates that genetic defects leading to primary skeletal muscle diseases might have been underdiagnosed, especially pathogenic variants in RYR1. We discuss three novel putative fetal akinesia genes: GCN1, IQSEC3 and RYR3. Of those, IQSEC3, and RYR3 had been proposed as neuromuscular disease-associated genes recently, and our findings endorse them as FA candidate genes. By combining NGS with deep clinical phenotyping, we achieved a 73% success rate of solved cases.

Novel insights into diabetes mellitus due to DNAJC3-defect: Evolution of neurological and endocrine phenotype in the pediatric age group.

BACKGROUND: A number of inborn errors of metabolism caused by abnormal protein trafficking that lead to endoplasmic reticulum storage diseases (ERSD) have been defined in the last two decades. One such disorder involves biallelic mutations in the gene encoding endoplasmic reticulum resident co-chaperone DNAJC3 (P58IPK ) that leads to diabetes in the second decade of life, in addition to multiple endocrine dysfunction and nervous system involvement. OBJECTIVE: The aim of this study was to define the natural history of this new form of diabetes, especially the course of abnormalities related to glucose metabolism. METHODS: Whole-exome and Sanger sequencing was used to detect DNAJC3 defect in two patients. Detailed analysis of their clinical history as well as biochemical, neurological and radiological studies were carried out to deduce natural history of neurological and endocrine phenotype. RESULTS: DNAJC3 defect led to beta-cell dysfunction causing hyperinsulinemichypoglycemia around 2 years of age in both patients, which evolved into diabetes with insulin deficiency in the second decade of life, probably due to beta cell loss. Endocrine phenotype involved severe early-onset growth failure due to growth hormone deficiency, and hypothyroidism of central origin. Neurological phenotype involved early onset sensorineural deafness discovered around 5 to 6 years, and neurodegeneration of central and peripheral nervous system in the first two decades of life. CONCLUSION: Biallelic loss-of-function in the ER co-chaperone DNAJC3 leads to a new form of diabetes with early onset hyperinsulinemic hypoglycemia evolving into insulin deficiency as well as severe growth failure, hypothyroidism and diffuse neurodegeneration.

A Revisited Diagnosis of Collagen VI Related Muscular Dystrophy in a Patient with a Novel COL6A2 Variant and 21q22.3 Deletion.

The genetic etiology of collagen VI related muscular dystrophies is heterogenous. Genomic deletions in one allele involving COL6A2 or both COL6A1 and COL6A2 unmasking a pathogenic variant in the second nondeleted allele have been described in the etiology. We aimed to report the clinical and molecular findings of a 13-year-old boy with ring chromosome 21 who presented to our clinic with easy fatigability, muscle weakness, and waddling gait. Phenotypic delineation along with chromosomal microarray analysis and DNA sequencing were performed. Affymetrix CytoScan Optima array platform and DNA sequencing revealed a 2,202 kb de novo deletion at 21q22.3, including COL6A1 and COL6A2, and a novel heterozygous variant at position c.2875G > A;p.(Glu959Lys) in COL6A2, respectively. Before his admission to our center, the patient was evaluated for hypotonia elsewhere when he was 15 months old. He was diagnosed with ring chromosome 21 on peripheral blood karyotype analysis; however, no further assessment was performed at that time. He had normal growth with mild dysmorphic facial features, distal laxity, gastrocnemius hypertrophy, proximal muscle weakness, increased lordotic posture with mild flexion contractures at the knees, and gait disturbance. Although the phenotype does not fit into classical Ullrich congenital muscular dystrophies, muscle magnetic resonance imaging (MRI) revealed a complementary pattern consistent with collagen VI related myopathies. Genetic testing confirmed the clinical diagnosis as well. This patient yet represents another example of the effect of large genomic deletions leading to recessive disorders through unmasking a pathogenic variant in the second nondeleted allele.

Recurrent Demyelinating Episodes as Sole Manifestation of Inherited CD59 Deficiency.

Defects in the regulatory components of the complement system can lead to inflammatory diseases. We present a patient who had four episodes of demyelination in the central nervous system as the only manifestation of inherited CD59 deficiency. Relapsing encephalopathy partially responsive to intravenous immunoglobulin and steroid treatments on the background of parental consanguinity suggested an inherited immune dysregulation. Next generation sequencing revealed homozygous mutation in the CD59 gene, confirmed by lack of CD59 expression on flow cytometry. Inherited CD59 deficiency is a rare autosomal recessive condition characterized by chronic hemolysis, recurrent strokes, and relapsing peripheral demyelinating neuropathy mimicking Guillain-Barré syndrome or chronic inflammatory demyelinating polyneuropathy. Recurrent central nervous system demyelinating episodes as the only manifestation has not been reported to date in inherited CD59 deficiency. This entity should be considered in the differential diagnosis of patients with early-onset recurrent neurological diseases with central or peripheral origin.

Diagnostic Pathway to Nonsense Mutation Dystrophinopathy: A Tertiary-Center, Retrospective Experience.

Up to 15% of Duchenne's muscular dystrophy (DMD) is caused by nonsense mutations (nm-DMD). In this study, we aimed to evaluate the age at diagnosis, presentations, and diagnostic approach in 43 nm-DMD boys. The mean age at presentation and diagnosis was 3 years and 4 years, respectively. Presenting signs or symptoms were asymptomatic creatine kinase (CK) elevation (40%), muscle weakness (30%), motor delay (18%), and walking difficulties (12%). Multiplex polymerase chain reaction (PCR) of the most commonly deleted exons were negative (n = 17), and muscle biopsy was consistent with dystrophinopathy (n = 24). In all patients, multiplex ligation-dependent probe amplification (MLPA) followed by direct sequencing of all exons, revealed nm-DMD. Mean age at genetic diagnosis was 6 years 8 months. Patients were evaluated in two-time periods, between 2006 and 2011 (Group I: n = 10) and 2011 and 2017 (Group II: n = 33). The mean age at diagnosis/genetic confirmation in Group I and in Group II was 3 years 9 months/10 years, and 4 years 1 month/5 years 9 months, respectively. Most frequently performed first step diagnostic tests in Group I and Group II were muscle biopsy and MLPA.Our study reflects the change in the age at genetic diagnosis and diagnostic approach to nm-DMD depending on the advances and availability of genetic testing.

Risk factors for seizure recurrence in a pediatric observation unit.

BACKGROUND: Most patients present with seizures to pediatric emergency department (PED) are observed for extended periods for the risk of possible acute recurrence. OBJECTIVE: The aim of this study is to determine the risk factors of acute recurrence within first 24 h. METHODS: Patients who presented to PED with seizure during past 24 h were enrolled. Demographic features, number and duration of seizures, diagnostic studies, physical examination findings, presence and time of seizure recurrence in PED were noted. RESULTS: 187 patients were eligible for the study. 46% had recurrence of seizures in 24 h, 90,8% of recurrence within the first 6 h. Univariate analysis showed that younger patients, epileptic patients who were on multiple antiepileptic drugs (AEDs), who had multiple seizures during the past 24 h, who had abnormal neurological examination or neuroimaging findings had increased risk of seizure recurrence. Multivariate analysis showed that number of seizures during the past 24 h and previous use of AEDs was significantly associated with increased risk of recurrence. CONCLUSION: Risk factors for acute recurrence should be evaluated for each patient. Patients without risk factors and no seizures during the first 6 h should not be observed for extended periods in PED.

SPEG interacts with myotubularin, and its deficiency causes centronuclear myopathy with dilated cardiomyopathy.

Centronuclear myopathies (CNMs) are characterized by muscle weakness and increased numbers of central nuclei within myofibers. X-linked myotubular myopathy, the most common severe form of CNM, is caused by mutations in MTM1, encoding myotubularin (MTM1), a lipid phosphatase. To increase our understanding of MTM1 function, we conducted a yeast two-hybrid screen to identify MTM1-interacting proteins. Striated muscle preferentially expressed protein kinase (SPEG), the product of SPEG complex locus (SPEG), was identified as an MTM1-interacting protein, confirmed by immunoprecipitation and immunofluorescence studies. SPEG knockout has been previously associated with severe dilated cardiomyopathy in a mouse model. Using whole-exome sequencing, we identified three unrelated CNM-affected probands, including two with documented dilated cardiomyopathy, carrying homozygous or compound-heterozygous SPEG mutations. SPEG was markedly reduced or absent in two individuals whose muscle was available for immunofluorescence and immunoblot studies. Examination of muscle samples from Speg-knockout mice revealed an increased frequency of central nuclei, as seen in human subjects. SPEG localizes in a double line, flanking desmin over the Z lines, and is apparently in alignment with the terminal cisternae of the sarcoplasmic reticulum. Examination of human and murine MTM1-deficient muscles revealed similar abnormalities in staining patterns for both desmin and SPEG. Our results suggest that mutations in SPEG, encoding SPEG, cause a CNM phenotype as a result of its interaction with MTM1. SPEG is present in cardiac muscle, where it plays a critical role; therefore, individuals with SPEG mutations additionally present with dilated cardiomyopathy.