Digenic inheritance involving a muscle-specific protein kinase and the giant titin protein causes a skeletal muscle myopathy.

In digenic inheritance, pathogenic variants in two genes must be inherited together to cause disease. Only very few examples of digenic inheritance have been described in the neuromuscular disease field. Here we show that predicted deleterious variants in SRPK3, encoding the X-linked serine/argenine protein kinase 3, lead to a progressive early onset skeletal muscle myopathy only when in combination with heterozygous variants in the TTN gene. The co-occurrence of predicted deleterious SRPK3/TTN variants was not seen among 76,702 healthy male individuals, and statistical modeling strongly supported digenic inheritance as the best-fitting model. Furthermore, double-mutant zebrafish (srpk3-/-; ttn.1+/-) replicated the myopathic phenotype and showed myofibrillar disorganization. Transcriptome data suggest that the interaction of srpk3 and ttn.1 in zebrafish occurs at a post-transcriptional level. We propose that digenic inheritance of deleterious changes impacting both the protein kinase SRPK3 and the giant muscle protein titin causes a skeletal myopathy and might serve as a model for other genetic diseases.

Loss-of-function variants in JPH1 cause congenital myopathy with prominent facial involvement.

Background: Weakness of facial, ocular, and axial muscles is a common clinical presentation in congenital myopathies caused by pathogenic variants in genes encoding triad proteins. Abnormalities in triad structure and function resulting in disturbed excitation-contraction coupling and Ca 2+ homeostasis can contribute to disease pathology. Methods: We analysed exome and genome sequencing data from three unrelated individuals with congenital myopathy characterised by striking facial, ocular, and bulbar involvement. We collected deep phenotypic data from the affected individuals. We analysed the RNA-seq data of one proband and performed gene expression outlier analysis in 129 samples. Results: The three probands had remarkably similar clinical presentation with prominent facial, ocular, and bulbar features. Disease onset was in the neonatal period with hypotonia, poor feeding, cleft palate and talipes. Muscle weakness was generalised but most prominent in the lower limbs with facial weakness also present. All patients had myopathic facies, bilateral ptosis, ophthalmoplegia and fatiguability. While muscle biopsy on light microscopy did not show any obvious morphological abnormalities, ultrastructural analysis showed slightly reduced triads, and structurally abnormal sarcoplasmic reticulum. DNA sequencing identified three unique homozygous loss of function variants in JPH1 , encoding junctophilin-1 in the three families; a stop-gain (c.354C>A; p.Tyr118*) and two frameshift (c.373del p.Asp125Thrfs*30 and c.1738del; p.Leu580Trpfs*16) variants. Muscle RNA-seq showed strong downregulation of JPH1 in the F3 proband. Conclusions: Junctophilin-1 is critical to the formation of skeletal muscle triad junctions by connecting the sarcoplasmic reticulum and T-tubules. Our findings suggest that loss of JPH1 results in a congenital myopathy with prominent facial, bulbar and ocular involvement. Key message: This study identified novel homozygous loss-of-function variants in the JPH1 gene, linking them to a unique form of congenital myopathy characterised by severe facial and ocular symptoms. Our research sheds light on the critical impact on junctophilin-1 function in skeletal muscle triad junction formation and the consequences of its disruption resulting in a myopathic phenotype. What is already known on this topic: Previous studies have shown that pathogenic variants in genes encoding triad proteins lead to various myopathic phenotypes, with clinical presentations often involving muscle weakness and myopathic facies. The triad structure is essential for excitation-contraction (EC) coupling and calcium homeostasis and is a key element in muscle physiology. What this study adds and how this study might affect research practice or policy: This study establishes that homozygous loss-of-function mutations in JPH1 cause a congenital myopathy predominantly affecting facial and ocular muscles. This study also provides clinical insights that may aid the clinicians in diagnosing similar genetically unresolved cases.

A pathogenic CTBP1 variant featuring HADDTS with dystrophic myopathology.

HADDTS (Hypotonia, Ataxia, Developmental-Delay and Tooth-enamel defects) is a newly emerging syndrome caused by CTBP1 mutations. Only five reports (13 cases) are available; three contained muscle-biopsy results but none presented illustrated histomyopathology. We report a patient in whom whole-exome sequencing revealed a heterozygous de novo CTBP1 missense mutation (c.1024 C>T; p.(Arg342Trp)). Progressive muscular weakness and myopathic electromyography suggested a myopathological substrate; muscle-biopsy revealed dystrophic features with endomysial-fibrosis, fiber-size variability, necrotic/degenerative vacuolar myopathy, sarcoplasmic/myofibrillar- and striation-alterations, and enzyme histochemical and structural mitochondrial alterations/defects including vacuolar mitochondriopathy. Our report expands the number of cases in this extremely rare condition and provides illustrated myopathology, muscle-MRI, and electron-microscopy. These are crucial for elucidating the nature and extent of the underlying myopathological-correlates and to characterize the myopatholgical phenotype spectrum in this genetic neurodevelopmental condition.

Loss of function variants in DNAJB4 cause a myopathy with early respiratory failure.

DNAJ/HSP40 co-chaperones are integral to the chaperone network, bind client proteins and recruit them to HSP70 for folding. We performed exome sequencing on patients with a presumed hereditary muscle disease and no genetic diagnosis. This identified four individuals from three unrelated families carrying an unreported homozygous stop gain (c.856A > T; p.Lys286Ter), or homozygous missense variants (c.74G > A; p.Arg25Gln and c.785 T > C; p.Leu262Ser) in DNAJB4. Affected patients presented with axial rigidity and early respiratory failure requiring ventilator support between the 1st and 4th decade of life. Selective involvement of the semitendinosus and biceps femoris muscles was seen on MRI scans of the thigh. On biopsy, muscle was myopathic with angular fibers, protein inclusions and occasional rimmed vacuoles. DNAJB4 normally localizes to the Z-disc and was absent from muscle and fibroblasts of affected patients supporting a loss of function. Functional studies confirmed that the p.Lys286Ter and p.Leu262Ser mutant proteins are rapidly degraded in cells. In contrast, the p.Arg25Gln mutant protein is stable but failed to complement for DNAJB function in yeast, disaggregate client proteins or protect from heat shock-induced cell death consistent with its loss of function. DNAJB4 knockout mice had muscle weakness and fiber atrophy with prominent diaphragm involvement and kyphosis. DNAJB4 knockout muscle and myotubes had myofibrillar disorganization and accumulated Z-disc proteins and protein chaperones. These data demonstrate a novel chaperonopathy associated with DNAJB4 causing a myopathy with early respiratory failure. DNAJB4 loss of function variants may lead to the accumulation of DNAJB4 client proteins resulting in muscle dysfunction and degeneration.

FXR1-related congenital myopathy: expansion of the clinical and genetic spectrum.

BACKGROUND: Biallelic pathogenic variants in FXR1 have recently been associated with two congenital myopathy phenotypes: a severe form associated with hypotonia, long bone fractures, respiratory insufficiency and infantile death, and a milder form characterised by proximal muscle weakness with survival into adulthood. OBJECTIVE: We report eight patients from four unrelated families with biallelic pathogenic variants in exon 15 of FXR1. METHODS: Whole exome sequencing was used to detect variants in FXR1. RESULTS: Common clinical features were noted for all patients, which included proximal myopathy, normal serum creatine kinase levels and diffuse muscle atrophy with relative preservation of the quadriceps femoris muscle on muscle imaging. Additionally, some patients with FXR1-related myopathy had respiratory involvement and required bilevel positive airway pressure support. Muscle biopsy showed multi-minicores and type I fibre predominance with internalised nuclei. CONCLUSION: FXR1-related congenital myopathy is an emerging entity that is clinically recognisable. Phenotypic variability associated with variants in FXR1 can result from differences in variant location and type and is also observed between patients homozygous for the same variant, rendering specific genotype-phenotype correlations difficult. Our work broadens the phenotypic spectrum of FXR1-related congenital myopathy.

A Multicentered Academic Medical Center Experience of a Simulated Root Cause Analysis (RCA) for Hematology/Oncology Fellows.

Quality improvement and patient safety education is an Accreditation Council for Graduate Medical Education (ACGME) common program requirement for hematology/oncology fellowships. Interprofessional clinical patient safety activities, such as root cause analyses (RCA), can be challenging to incorporate into busy schedules. We report on a multicentered experience utilizing a simulated RCA educational module in an attempt to provide fellows with the tools needed to participate in a live RCA and to increase awareness of the need to analyze patient safety events. The 2-h module included a didactic session explaining the basics of an RCA including common terminology, effective chart review, and personal interviews. The fellows assessed a patient safety event of a missed coagulopathy and created an event flow map and fishbone analysis. They then formed root cause/contributing factor statements and proposed a solution. Twenty-three fellows from two institutions completed the experience. There was a significant difference in fellow reported comfort with participating in a live RCA (p = 0.03), and in utilizing the tools of an RCA following the mock RCA experience (p = 0.005). About 70% of respondents felt that as a result of the mock RCA, they were more likely to report a near miss or adverse event and were more likely to be thorough in their documentation. Mock RCAs are a feasible method of incorporating ACGME-required patient safety activities into hematology/oncology fellow education and are effective in increasing their comfort and understanding of important quality improvement skills.

Satisfaction of General Versus Specialized Continuity Clinic in Hematology Oncology Fellowship Training: A Survey.

BACKGROUND: At the University of Florida (UF), hematology-oncology (HO) fellows participate in 2 general types of continuity clinic as part of their fellowship training. One clinic, at the Veterans Hospital (VA), allows fellows to care for patients with a variety of hematology oncology diagnoses in a general clinic setting. The other clinic, located at the university site, is disease or system specific (such as breast or GI clinic). Considerable research supports the value of continuity clinic in residency and fellowship training, but the differences in having a general versus specialized clinic for HO fellows have not been explored. The purpose of this study was to investigate the perceived differences of general versus specialized continuity clinics by recent HO graduates from UF. Specifically, we were interested in learning which features of a continuity clinic they felt were most impactful for their current clinical practice. METHODS: An anonymous survey was sent to the last 6 graduating classes of HO fellows at UF, between years of 2013 and 2018. The survey contained short demographic questions, followed by 5 open ended questions pertaining to the differing continuity clinic experiences. Graduates were asked about their opinions of both the general and specialized clinics during their training at UF. Survey responses were reviewed and coded for common themes by the authors. RESULTS: Of 28 graduating fellows surveyed, 13 responded to the survey (response rate 46%). In thematic review of survey responses, the most common themes that emerged concerned autonomy, level of supervision, and the diversity of the patient population. A majority of respondents felt they had more autonomy and personal responsibility at the VA general clinic, but less direct supervision than at the specialized clinics. They also believed they got a broader exposure to different disease types at the VA general clinic. Surveyed participants also commented on the quality of educational seminars and activities, preceptor expertise and teaching, and ability to observe cutting edge practice and clinical trials. CONCLUSIONS: Graduated oncology fellows from UF believe that there is a balance that exists between having autonomy and ownership of their patients versus having adequate supervision. Many believe that having "controlled autonomy" and "as much independence as is safe for patients" is key to a meaningful continuity clinic experience during oncology fellowship training.

Late onset Sandhoff disease presenting with lower motor neuron disease and stuttering.

Defects in the HEXB gene which encodes the ß-subunit of ß-hexosaminidase A and B enzymes, cause a GM2 gangliosidosis, also known as Sandhoff disease, which is a rare lysosomal storage disorder. The most common form of the disease lead to quickly progressing mental and motor decline in infancy; however there are other less severe forms with later onset that can also involve lower motor neurons. The diagnosis of this disease is based on low serum ß-hexosaminidases A and B levels and confirmed using genetic test. We report two siblings with compound heterozygous HEXB mutations whose phenotype was extremely mild consisting in stuttering in both cases associated to mild proximal weakness in one of the cases, broadening the clinical spectrum of late onset Sandhoff disease.

A cryptic intronic LAMA2 insertion in a boy with mild congenital muscular dystrophy type 1A.

Recessive mutations in the LAMA2 gene lead to congenital muscular dystrophy type 1A and limb girdle muscular dystrophy R23 with complete or partial laminin α2 chain deficiency. Complete laminin α2 chain deficiency presents with early onset of severe hypotonia and generalized weakness, whereas partial deficiency shows a milder and more variable course with limb girdle weakness. Here, we report a child with mildly delayed motor development, elevated serum creatine kinase levels (>1000 U/l) and brain white matter hypointensity, indicative of laminin α2 chain deficiency. In addition to a stop gain variant in exon 39, the patient was found to carry an intronic insertion of 72 bp in intron 38 of the LAMA2 gene in trans. RNA analysis revealed that this insertion results in abnormally spliced as well as wild type transcript, which explains the partial laminin α2 chain deficiency observed in the muscle biopsy.

Three Individuals with PURA Syndrome in a Cohort of Patients with Neuromuscular Disease.

Pur-α protein (PURA) syndrome manifests in early childhood with core features such as neurodevelopmental and speech delay, feeding difficulties, epilepsy, and hypotonia at birth. We identified three cases with PURA syndrome in a cohort of patients with unexplained muscular weakness, presenting with a predominantly neuromuscular and ataxic phenotype. We further characterize the clinical presentation of PURA syndrome including myopathic facies and muscular weakness as the main clinical symptoms in combination with elevated serum creatine kinase levels. Furthermore, we report two novel variants located in the conservative domains PUR-I and PUR-II. For the first time, we present the muscle biopsies of PURA syndrome patients, showing myopathic changes, fiber size variability, and fast fiber atrophy as the key features. PURA syndrome should be taken into consideration as a differential diagnosis in pediatric patients with unexplained muscle weakness.

Metabolic shift underlies recovery in reversible infantile respiratory chain deficiency.

Reversible infantile respiratory chain deficiency (RIRCD) is a rare mitochondrial myopathy leading to severe metabolic disturbances in infants, which recover spontaneously after 6-months of age. RIRCD is associated with the homoplasmic m.14674T>C mitochondrial DNA mutation; however, only ~ 1/100 carriers develop the disease. We studied 27 affected and 15 unaffected individuals from 19 families and found additional heterozygous mutations in nuclear genes interacting with mt-tRNAGlu including EARS2 and TRMU in the majority of affected individuals, but not in healthy carriers of m.14674T>C, supporting a digenic inheritance. Our transcriptomic and proteomic analysis of patient muscle suggests a stepwise mechanism where first, the integrated stress response associated with increased FGF21 and GDF15 expression enhances the metabolism modulated by serine biosynthesis, one carbon metabolism, TCA lipid oxidation and amino acid availability, while in the second step mTOR activation leads to increased mitochondrial biogenesis. Our data suggest that the spontaneous recovery in infants with digenic mutations may be modulated by the above described changes. Similar mechanisms may explain the variable penetrance and tissue specificity of other mtDNA mutations and highlight the potential role of amino acids in improving mitochondrial disease.

Homozygous TAF1C variants are associated with a novel childhood-onset neurological phenotype.

TATA-box binding protein associated factor, RNA polymerase I subunit C (TAF1C) is a component of selectivity factor 1 belonging to RNA polymerase I (Pol I) transcription machinery. We report two unrelated patients with homozygous TAF1C missense variants and an early onset neurological phenotype with severe global developmental delay. Clinical features included lack of speech and ambulation and epilepsy. MRI of the brain demonstrated widespread cerebral atrophy and frontal periventricular white matter hyperintensity. The phenotype resembled that of a previously described variant of UBTF, which encodes another transcription factor of Pol I. TAF1C variants were located in two conserved amino acid positions and were predicted to be deleterious. In patient-derived fibroblasts, TAF1C mRNA and protein expression levels were substantially reduced compared with healthy controls. We propose that the variants impairing TAF1C expression are likely pathogenic and relate to a novel neurological disease. This study expands the disease spectrum related to Pol I transcription machinery, associating the TAF1C missense variants with a severe neurological phenotype for the first time.

Sequential targeted exome sequencing of 1001 patients affected by unexplained limb-girdle weakness.

PURPOSE: Several hundred genetic muscle diseases have been described, all of which are rare. Their clinical and genetic heterogeneity means that a genetic diagnosis is challenging. We established an international consortium, MYO-SEQ, to aid the work-ups of muscle disease patients and to better understand disease etiology. METHODS: Exome sequencing was applied to 1001 undiagnosed patients recruited from more than 40 neuromuscular disease referral centers; standardized phenotypic information was collected for each patient. Exomes were examined for variants in 429 genes associated with muscle conditions. RESULTS: We identified suspected pathogenic variants in 52% of patients across 87 genes. We detected 401 novel variants, 116 of which were recurrent. Variants in CAPN3, DYSF, ANO5, DMD, RYR1, TTN, COL6A2, and SGCA collectively accounted for over half of the solved cases; while variants in newer disease genes, such as BVES and POGLUT1, were also found. The remaining well-characterized unsolved patients (48%) need further investigation. CONCLUSION: Using our unique infrastructure, we developed a pathway to expedite muscle disease diagnoses. Our data suggest that exome sequencing should be used for pathogenic variant detection in patients with suspected genetic muscle diseases, focusing first on the most common disease genes described here, and subsequently in rarer and newly characterized disease genes.

Expanding the disease phenotype of ADSSL1-associated myopathy in non-Korean patients.

Adenylosuccinate synthase (ADSSL1) is a muscle specific enzyme involved in the purine nucleotide cycle and responsible for the conversion of inosine monophosphate to adenosine monophosphate. Since 2016, when mutations in the ADSSL1 gene were first described to be associated with an adult onset distal myopathy, nine patients with compound heterozygous variants in the ADSSL1 gene, all of Korean origin, have been identified. Here we report a novel ADSSL1 mutation and describe two sporadic cases of Turkish and Indian origin. Many of the clinical features of both patients and muscle histopathology and muscle MRI findings, were in accordance with previously reported findings in the adult onset distal myopathy individuals. However, one of our patients presented with progressive, proximally pronounced weakness, severe muscle atrophy and early contractures. Thus, mutations in ADSSL1 have to be considered in patients with both distal and proximal muscle weakness and across various ethnicities.

Multiple acyl-coenzyme A dehydrogenase deficiency shows a possible founder effect and is the most frequent cause of lipid storage myopathy in Iran.

INTRODUCTION: Multiple acyl-coenzyme A dehydrogenase deficiency disorder (MADD) is a relatively rare disorders of lipid metabolism. This study aimed to investigate the demographic, clinical, and genetic features of MADD in Iran. METHODS: Twenty-nine patients with a definite diagnosis of lipid storage myopathy were recruited. All patients were tested for mutation in the ETFDH gene, and 19 had a biallelic mutation in this gene. RESULTS: Of 19 patients with definite mutations, 11 (57.9%) were female, and the median age was 31 years. Twelve patients had c.1130 T > C (p.L377P) mutation in exon 10. Two patients had two novel heterozygote pathogenic variants (c.679C > T (p.P227S) in exon 6 and c.814G > A (p.G272R) in exon 7) and two patients had c.1699G > A (p.E567K) in exon 13. Before treatment, the median muscle power was 4.6 (IQR: 4-4.7) that increased to 5 (IQR: 5-5) after treatment (Z = -3.71, p = .000). The median CK was 1848 U/l (IQR: 1014-3473) before treatment, which declined to 188 U/l (IQR: 117-397) after treatment (Z = -3.41, p = .001). Sixteen patients (84.2%) had full recovery after the treatment. The disease onset was earlier (12 years of age; IQR: 6-18) in patients with homozygous c.1130 T > C; p.(L377P) mutation compared to other ETFDH mutations (30 years of age; IQR: 20-35) (p = .00). DISCUSSION: MADD has different clinical presentations. As the patients respond favorably to treatment, early diagnosis and treatment may prevent the irreversible complications of the disease.

Clinical presentation and proteomic signature of patients with TANGO2 mutations.

Transport And Golgi Organization protein 2 (TANGO2) deficiency has recently been identified as a rare metabolic disorder with a distinct clinical and biochemical phenotype of recurrent metabolic crises, hypoglycemia, lactic acidosis, rhabdomyolysis, arrhythmias, and encephalopathy with cognitive decline. We report nine subjects from seven independent families, and we studied muscle histology, respiratory chain enzyme activities in skeletal muscle and proteomic signature of fibroblasts. All nine subjects carried autosomal recessive TANGO2 mutations. Two carried the reported deletion of exons 3 to 9, one homozygous, one heterozygous with a 22q11.21 microdeletion inherited in trans. The other subjects carried three novel homozygous (c.262C>T/p.Arg88*; c.220A>C/p.Thr74Pro; c.380+1G>A), and two further novel heterozygous (c.6_9del/p.Phe6del); c.11-13delTCT/p.Phe5del mutations. Immunoblot analysis detected a significant decrease of TANGO2 protein. Muscle histology showed mild variation of fiber diameter, no ragged-red/cytochrome c oxidase-negative fibers and a defect of multiple respiratory chain enzymes and coenzyme Q10 (CoQ10 ) in two cases, suggesting a possible secondary defect of oxidative phosphorylation. Proteomic analysis in fibroblasts revealed significant changes in components of the mitochondrial fatty acid oxidation, plasma membrane, endoplasmic reticulum-Golgi network and secretory pathways. Clinical presentation of TANGO2 mutations is homogeneous and clinically recognizable. The hemizygous mutations in two patients suggest that some mutations leading to allele loss are difficult to detect. A combined defect of the respiratory chain enzymes and CoQ10 with altered levels of several membrane proteins provides molecular insights into the underlying pathophysiology and may guide rational new therapeutic interventions.

Survival trends of metastatic small intestinal neuroendocrine tumor: a population-based analysis of SEER database.

BACKGROUND: Incidence of small intestinal neuroendocrine tumors (SNETs) is increasing and they now comprise the most common types of small intestinal cancer. SNETs frequently present with distant metastasis. Significant uncertainty prevails with regards to the surgical management strategies in metastatic SNETs. Therefore, we aim to analyze survival trends in metastatic SNET patients stratified by type of surgical treatment. METHODS: We analyzed the data from the SEER database: Incidence - SEER 18 Regs Research Data + Hurricane Katrina Impacted Louisiana Cases, Nov 2016 Sub (1973-2014 varying). Relative survival rates (RSRs) and hazard ratios (HRs) were measured for patients diagnosed with metastatic SNET between 2000 and 2014. Treatment received was divided into two broad categories; surgical resection and no surgery and further subcategorized into local resection (LR) (surgery of the primary tumor only) and radical resection (RR) (surgery for primary tumor and metastasectomy). RESULTS: We identified 1,138 metastatic SNET cases. Median age was 61 years. Median survival was 41 months and 5 year RSR was 72%. Age >50 years (HR 2.10, P<0.001), poorly differentiated histology (HR 3.50, P<0.001) and tumor size >2 cm (HR 1.27, P=0.07), showed poor outcome. The group which did not receive any tumor directed surgery showed the worst survival (5 years RSR 45.30% vs. 76%, respectively for no surgery vs. surgery group, P<0.001). We found no significant difference in survival between LR and RR (HR 1.01, 95% CI: 0.73-1.40, P=0.92). Upon further stratification, surgery significantly improved survival on patients who were >50 years (HR 0.37), and for primary tumor location in the duodenum (HR 0.13). CONCLUSIONS: Surgery for the primary tumor (LR or RR) significantly improved 5-year survival even in the presence of distant metastasis irrespective of primary tumor size, grade, or histology. Poor prognostic factors include, age >50 years, duodenal primary, tumor size >2 cm, and poorly differentiated histology.

Clonal expansion of mtDNA deletions: different disease models assessed by digital droplet PCR in single muscle cells.

Deletions in mitochondrial DNA (mtDNA) are an important cause of human disease and their accumulation has been implicated in the ageing process. As mtDNA is a high copy number genome, the coexistence of deleted and wild-type mtDNA molecules within a single cell defines heteroplasmy. When deleted mtDNA molecules, driven by intracellular clonal expansion, reach a sufficiently high level, a biochemical defect emerges, contributing to the appearance and progression of clinical pathology. Consequently, it is relevant to determine the heteroplasmy levels within individual cells to understand the mechanism of clonal expansion. Heteroplasmy is reflected in a mosaic distribution of cytochrome c oxidase (COX)-deficient muscle fibers. We applied droplet digital PCR (ddPCR) to single muscle fibers collected by laser-capture microdissection (LCM) from muscle biopsies of patients with different paradigms of mitochondrial disease, characterized by the accumulation of single or multiple mtDNA deletions. By combining these two sensitive approaches, ddPCR and LCM, we document different models of clonal expansion in patients with single and multiple mtDNA deletions, implicating different mechanisms and time points for the development of COX deficiency in these molecularly distinct mitochondrial cytopathies.

Multifocal demyelinating motor neuropathy and hamartoma syndrome associated with a de novo PTEN mutation.

OBJECTIVE: To describe a patient with a multifocal demyelinating motor neuropathy with onset in childhood and a mutation in phosphatase and tensin homolog (PTEN), a tumor suppressor gene associated with inherited tumor susceptibility conditions, macrocephaly, autism, ataxia, tremor, and epilepsy. Functional implications of this protein have been investigated in Parkinson and Alzheimer diseases. METHODS: We performed whole-exome sequencing in the patient's genomic DNA validated by Sanger sequencing. Immunoblotting, in vitro enzymatic assay, and label-free shotgun proteomic profiling were performed in the patient's fibroblasts. RESULTS: The predominant clinical presentation of the patient was a childhood onset, asymmetric progressive multifocal motor neuropathy. In addition, he presented with macrocephaly, autism spectrum disorder, and skin hamartomas, considered as clinical criteria for PTEN-related hamartoma tumor syndrome. Extensive tumor screening did not detect any malignancies. We detected a novel de novo heterozygous c.269T>C, p.(Phe90Ser) PTEN variant, which was absent in both parents. The pathogenicity of the variant is supported by altered expression of several PTEN-associated proteins involved in tumorigenesis. Moreover, fibroblasts showed a defect in catalytic activity of PTEN against the secondary substrate, phosphatidylinositol 3,4-trisphosphate. In support of our findings, focal hypermyelination leading to peripheral neuropathy has been reported in PTEN-deficient mice. CONCLUSION: We describe a novel phenotype, PTEN-associated multifocal demyelinating motor neuropathy with a skin hamartoma syndrome. A similar mechanism may potentially underlie other forms of Charcot-Marie-Tooth disease with involvement of the phosphatidylinositol pathway.