Re-evaluation of PRRT2 mutations in paroxysmal disorders

Mutations in PRRT2 have recently been identified as the major cause of autosomal dominant benign familial infantile epilepsy (BFIE), infantile convulsions with choreoathetosis syndrome (ICCA), and paroxysmal kinesigenic dyskinesia (PKD). Other paroxysmal disorders like febrile seizures, migraine, paroxysmal exercise-induced dyskinesia, and paroxysmal non-kinesigenic dyskinesia have also been shown to be associated with this gene. We re-evaluated PRRT2 mutations and genetic–clinical correlations in additional cases with PKD/ICCA and other paroxysmal disorders. Two novel mutations in PRRT2 were revealed in PKD/ICCA cases, while no mutations were detected in other diseases, which suggests BFIE and PKD are still core phenotypes of PRRT2-related spectrum disorders.     

Mutations in PRRT2 are not a common cause of infantile epileptic encephalopathies

Heterozygous mutations in PRRT2 have recently been identified as the major cause of autosomal dominant benign familial infantile epilepsy (BFIE), infantile convulsions with choreoathetosis syndrome (ICCA), and paroxysmal kinesigenic dyskinesia (PKD). Homozygous mutations in PRRT2 have also been reported in two families with intellectual disability (ID) and seizures. Heterozygous mutations in the genes KCNQ2 and SCN2A cause the two other autosomal dominant seizure disorders of infancy: benign familial neonatal epilepsy and benign familial neonatal‐infantile epilepsy. Mutations in KCNQ2 and SCN2A also contribute to severe infantile epileptic encephalopathies (IEEs) in which seizures and intellectual disability co‐occur. We therefore hypothesized that PRRT2 mutations may also underlie cases of IEE. We examined PRRT2 for heterozygous, compound heterozygous or homozygous mutations to determine their frequency in causing epileptic encephalopathies (EEs). Two hundred twenty patients with EEs with onset by 2 years were phenotyped. An assay for the common PRRT2 c.649‐650insC mutation and high resolution‐melt analysis for mutations in the remaining exons of PRRT2 were performed. Neither the common mutation nor any other pathogenic variants in PRRT2 were detected in the 220 patients. Our findings suggest that mutations in PRRT2 are not a common cause of IEEs.     

Familial PRRT2 mutation with heterogeneous paroxysmal disorders including paroxysmal torticollis and hemiplegic migraine

PRRT2 is the gene recently associated with paroxysmal kinesigenic dyskinesia (PKD), benign familial infantile epilepsy, and choreoathetosis infantile convulsions. We report four family members with PRRT2 mutations who had heterogeneous paroxysmal disorders. The index patient had transient infantile paroxysmal torticollis, then benign infantile epilepsy that responded to carbamazepine. The index patient's father had PKD and migraine with aphasia, and his two brothers had hemiplegic migraine with onset in childhood. All four family members had the same PRRT2 c.649dupC mutation. We conclude that heterogeneous paroxysmal disorders are associated with PRRT2 mutations and include paroxysmal torticollis and hemiplegic migraine. We propose that PRRT2 is a new gene for hemiplegic migraine.     

Homozygous c.649dupC mutation in PRRT2 worsens the BFIS/PKD phenotype with mental retardation,episodic ataxia,and absences

Heterozygous mutations of PRRT2, which encodes proline‐rich transmembrane protein 2, are associated with heterogeneous phenotypes including benign familial infantile seizures (BFIS), or familial paroxysmal kinesigenic dystonia (PKD). We report a consanguineous Italian family with BFIS/PKD phenotype that contained 14 living members with 6 affected individuals (four men, ranging in age from 6–44 years). We identified the reported c.649dupC (p.Arg217ProfsX8) mutation of PRRT2 gene that cosegregated with the disease and was not observed in 100 controls of matched ancestry. Four patients with BFIS phenotype were heterozygous for this mutation, including the consanguineous parents of the two affected brothers with more severe phenotypes of BFIS/PKD—mental retardation, episodic ataxia, and absences—who were the only individuals to carry a homozygous c.649dupC mutation. This family provides strong evidence that homozygous PRRT2 mutations give rise to more severe clinical disease of mental retardation, episodic ataxia, and absences, and, thus, enlarges the clinical spectrum related to PRRT2 mutations. Moreover, it suggests an additive effect of double dose of the genetic mutation and underscores the complexity of the phenotypic consequences of mutations in this gene.     

Acute-Onset Ataxia and Transient Cerebellar Diffusion Restriction Associated with a PRRT2 Mutation

PRRT2 gene mutations cause paroxysmal kinesigenic dyskinesia (PKD), infantile convulsions, hemiplegic migraine, and episodic ataxia. A 21-year-old woman reported an episode of dizziness and ataxic gait occurring after swimming. Brain MRI showed a hyperintense cerebellar lesion on diffusion-weighted imaging (DWI) with decreased apparent diffusion coefficient. The clinical course was favorable. Both clinical and MRI abnormalities regressed. Her brother had presented PKD since adulthood. A C.649dupC PRRT2 truncating mutation was identified in both patients. To our knowledge, this is the first case of an acute cerebellar ataxia associated with heterozygous PRRT2 mutation and transient cerebellar hyperintensity on DWI. Among the clinical and genetic heterogeneities of familial paroxysmal disorders, PRRT2 mutation may be considered in patients with episodic cerebellar ataxia and diffusion restriction on neuroimaging.     

A new case of concurrent existence of PRRT2-associated paroxysmal movement disorders with c.649dup variant and 16p11.2 microdeletion syndrome

BackgroundThe PRRT2 gene located at 16p11.2 encodes proline-rich transmembrane protein 2. In recent reviews, clinical spectrum caused by pathogenic PRRT2 variants is designated as PRRT2-associated paroxysmal movement disorders, which include paroxysmal kinesigenic dyskinesia, benign familial infantile epilepsy, and infantile convulsions with choreoathetosis, and hemiplegic migraine. The recurrent 16p11.2 microdeletion encompassing PRRT2 has also been reported to cause neurodevelopmental syndrome, associated with autism spectrum disorder. Although PRRT2 variants and 16p11.2 microdeletion cause each disease with the autosomal dominant manner, rare cases with bi-allelic PRRT2 variants or concurrent existence of PRRT2 variants and 16p11.2 microdeletion have been reported to show more severe phenotypes.Case reportA 22-year-old man presents with episodic ataxia, paroxysmal kinesigenic dyskinesia, seizure, intellectual disability and autism spectrum disorder. He also has obesity, hypertension, hyperuricemia, and mild liver dysfunction. Exome sequencing revealed a c.649dup variant in PRRT2 in one allele and a de novo 16p11.2 microdeletion in another allele.ConclusionsOur case showed combined clinical features of PRRT2-associated paroxysmal movement disorders and 16p11.2 microdeletion syndrome. We reviewed previous literatures and discussed phenotypic features of patients who completely lack the PRRT2 protein.     

PRRT2 mutations in a cohort of Chinese families with paroxysmal kinesigenic dyskinesia and genotype–phenotype correlation reanalysis in literatures

Purpose of the study: Though rare, children are susceptible to paroxysmal dyskinesias such as paroxysmal kinesigenic dyskinesia, and infantile convulsions and choreoathetosis. Recent studies showed that the cause of paroxysmal kinesigenic dyskinesia or infantile convulsions and choreoathetosis could be proline-rich transmembrane protein 2 (PRRT2) gene mutations.

Material and methods: This study analysed PRRT2 gene mutations in 51 families with paroxysmal kinesigenic dyskinesia or infantile convulsions and choreoathetosis by direct sequencing. In particular, we characterize the genotype–phenotype correlation between age at onset and the types of PRRT2 mutations in all published cases.

Results: Direct sequencing showed that 12 out of the 51 families had three different pathogenic mutations (c.649dupC, c.776dupG, c.649C>T) in the PRRT2 gene. No significant difference of age at onset between the patients with and without PRRT2 mutations was found in this cohort of patients. A total of 97 different PRRT2 mutations have been reported in 87 studies till now. The PRRT2 mutation classes are wide, and most mutations are frameshift mutations but the most common mutation remains c.649dupC. Comparisons of the age at onset in paroxysmal kinesigenic dyskinesia or infantile convulsions patients with different types of mutations showed no significant difference.

Conclusions: This study expands the clinical and genetic spectrums of Chinese patients with paroxysmal kinesigenic dyskinesia and infantile convulsions and choreoathetosis. No clear genotype–phenotype correlation between the age at onset and the types of mutations has been determined.     

Benign infantile seizures followed by autistic regression in a boy with 16p11.2 deletion

Benign infantile seizures (BIS) are usually a self‐limiting condition, which may be associated with heterozygous mutations in the PRRT2 gene at chromosome 16p11.2. Here, we report a boy with a deletion in 16p11.2, presenting with BIS and typical neurodevelopment in the first year of life, unexpectedly followed by severe autistic regression. 16p11.2 deletions are typically associated with intellectual disability, autism, and language disorders, and only rarely with BIS. This clinical report shows that the neurodevelopmental prognosis in BIS patients may not always be benign, and suggests that array CGH screening should be considered for affected infants in order to rule out deletions at 16p11.2 and long‐term clinical follow‐up.     

Mutation screening of the PRRT2 gene for benign epilepsy with centrotemporal spikes in Chinese mainland population

Proline-rich transmembrane protein 2 gene (PRRT2) mutations are reported to cause common paroxysmal neurological disorders and show a remarkable pleiotropy. Benign epilepsy with centrotemporal spikes (BECTS) is considered to be the most common epilepsy syndrome in childhood. It is placed among the idiopathic localization related epilepsies. Recently, it was reported that a girl with a PRRT2 mutation c.649_650insC developed infantile focal epilepsy with bilateral spikes which resembled the rolandic spikes. Hereby we performed a comprehensive genetic mutation screening of PRRT2 gene in a cohort of 53 sporadic BECTS patients. None of the 53 sporadic BECTS patients and other 250 controls carried mutations including c.649_650insC in PRRT2. Our data indicated that the PRRT2 mutations might most likely not be associated with BECTS in Chinese mainland population.     

PRRT2 mutation in Japanese children with benign infantile epilepsy

Mutations in PRRT2 genes have been identified as a major cause of benign infantile epilepsy and/or paroxysmal kinesigenic dyskinesia. We explored mutations in PRRT2 in Japanese patients with BIE as well as its related conditions including convulsion with mild gastroenteritis and benign early infantile epilepsy. We explored PRRT2 mutations in Japanese children who had had unprovoked infantile seizures or convulsion with mild gastroenteritis. The probands included 16 children with benign infantile epilepsy, 6 children with convulsions with mild gastroenteritis, and 2 siblings with benign early infantile epilepsy. In addition, we recruited samples from family members when PRRT2 mutation was identified in the proband. Statistical analyses were performed to identify differences in probands with benign infantile epilepsy according to the presence or absence of PRRT2 mutation. Among a total of 24 probands, PRRT2 mutations was identified only in 6 probands with benign infantile epilepsy. A common insertion mutation, c.649_650insC, was found in 5 families and a novel missense mutation, c.981C>G (I327M), in one. The family history of paroxysmal kinesigenic dyskinesia was more common in probands with PRRT2 mutations than in those without mutations. Our study revealed that PRRT2 mutations are common in Japanese patients with benign infantile epilepsy, especially in patients with a family history of paroxysmal kinesigenic dyskinesia.     

Peri-ictal EEG in infants with PRRT2-related self-limited infantile epilepsy

Objective

Pathogenic PRRT2 variants cause self-limited (familial) infantile epilepsy (SeLIE), which is responsive to sodium channel blocking antiseizure medications. The interictal EEG is typically normal. We describe a cohort of infants with PRRT2-related SeLIE with striking peri-ictal EEG abnormalities.

Methods

We included all infants diagnosed with PRRT2-related SeLIE during July 2020 to November 2021 at the Royal Children's Hospital, Melbourne. Clinical features and results of aetiologic investigations were collected from electronic medical records. All EEGs were reviewed independently by two epileptologists.

Results

Ten infants presented with focal seizures at a median age of 5 months (range: 3–6 months). Eight had a family history of epilepsy, paroxysmal kinesigenic dyskinesia (PKD) or hemiplegic migraine. Seven of the eight infants with an EEG performed within 24 h of the most recent seizure had epileptiform discharges. Their EEGs showed focal sharp waves, spikes, polyspikes or fast activity independently over the left and right temporo-occipital regions. Conversely, the two infants with last known seizure greater than 24 h prior to their EEG had no epileptiform discharges. Oxcarbazepine was commenced in two infants and was effective. Eight infants were initially treated with levetiracetam, and all were subsequently switched to oxcarbazepine due to ongoing seizures or side effects.

Significance

Posterior polymorphic focal epileptiform discharges on a peri-ictal EEG recording are a feature of PRRT2-related SeLIE. This finding, particularly in the presence of a family history of infantile epilepsy, PKD or hemiplegic migraine, suggests a diagnosis of PRRT2-related SeLIE and has important treatment implications.     

Phenotypic overlap among paroxysmal dyskinesia subtypes: Lesson from a family with PRRT2 gene mutation

Paroxysmal dyskinesia (PD) is a group of rare neurological conditions which was divided into paroxysmal kinesigenic dyskinesia (PKD), paroxysmal non-kinesigenic dyskinesia (PNKD) and paroxysmal exercise-induced dyskinesia (PED) according to their clinical features. PRRT2 gene was initially identified as the major gene responsible for PKD followed by presence of various PRRT2 mutations discovered in families with benign familial infantile convulsions (BFIC) and infantile convulsions and choreoathetosis (ICCA). We describe a family with characteristic PD showing overlaps in clinical pictures among the three PD subgroups, and a nonsense PRRT2 mutation c.649C > T (p.Arg217X) was also detected. This broadens the phenotypic spectrum in PRRT2-related disorders. In addition, an unusual exercise trigger observed in the proband, likely representing an underestimated occurrence, together with the current clinical PD classification is also elucidated.     

Autism‐associated Shank3 mutations alter mGluR expression and mGluR‐dependent but not NMDA receptor‐dependent long‐term depression

SHANK3 is a postsynaptic structural protein localized at excitatory glutamatergic synapses in which deletions and mutations have been implicated in patients with autism spectrum disorders (ASD). The expression of Shank3 ASD mutations causes impairments in ionotropic glutamate receptor‐mediated synaptic responses in neurons, which is thought to underlie ASD‐related behaviors, thereby indicating glutamatergic synaptopathy as one of the major pathogenic mechanisms. However, little is known about the functional consequences of ASD‐associated mutations in Shank3 on another important set of glutamate receptors, group I metabotropic glutamate receptors (mGluRs). Here, we further assessed how Shank3 mutations identified in patients with ASD (one de novo InsG mutation and two inherited point mutations, R87C and R375C) disrupt group I mGluR (mGluR1 and mGluR5) expression and function. To identify potential isoform‐specific deficits induced by ASD‐associated Shank3 mutations on group I mGluRs, we surface immunolabeled mGluR1 and mGluR5 independently. We also induced mGluR‐dependent synaptic plasticity (R,S‐3,5‐dihydroxyphenylglycine [DHPG]‐induced long‐term depression [LTD]) as well as N‐methyl‐D‐aspartate receptor (NMDAR)‐dependent LTD. ASD‐associated mutations in Shank3 differentially interfered with the ability of cultured hippocampal neurons to express mGluR5 and mGluR1 at synapses. Intriguingly, all ASD Shank3 mutations impaired mGluR‐dependent LTD without altering NMDAR‐dependent LTD. Our data show that the specific perturbation in mGluR‐dependent synaptic plasticity occurs in neurons expressing ASD‐associated Shank3 mutations, which may underpin synaptic dysfunction and subsequent behavioral deficits in ASD.     

PIGO mutations in intractable epilepsy and severe developmental delay with mild elevation of alkaline phosphatase levels

Aberrations in the glycosylphosphatidylinositol (GPI)–anchor biosynthesis pathway constitute a subclass of congenital disorders of glycosylation, and mutations in seven genes involved in this pathway have been identified. Among them, mutations in PIGV and PIGO, which are involved in the late stages of GPI‐anchor synthesis, and PGAP2, which is involved in fatty‐acid GPI‐anchor remodeling, are all causative for hyperphosphatasia with mental retardation syndrome (HPMRS). Using whole exome sequencing, we identified novel compound heterozygous PIGO mutations (c.389C>A [p.Thr130Asn] and c.1288C>T [p.Gln430*]) in two siblings, one of them having epileptic encephalopathy. GPI‐anchored proteins (CD16 and CD24) on blood granulocytes were slightly decreased compared with a control and his mother. Our patients lacked the characteristic features of HPMRS, such as facial dysmorphology (showing only a tented mouth) and hypoplasia of distal phalanges, and had only a mild elevation of serum alkaline phosphatase (ALP). Our findings therefore expand the clinical spectrum of GPI‐anchor deficiencies involving PIGO mutations to include epileptic encephalopathy with mild elevation of ALP.     

Genetic analysis of PRRT2 for benign infantile epilepsy,infantile convulsions with choreoathetosis syndrome,and benign convulsions with mild gastroenteritis

Purpose: PRRT2 mutations were recently identified in benign familial infantile epilepsy (BFIE) and infantile convulsions with paroxysmal choreoathetosis (ICCA) but no abnormalities have so far been identified in their phenotypically similar seizure disorder of benign convulsions with mild gastroenteritis (CwG), while mutations in KCNQ2 and KCNQ3 have been recognized in benign familial neonatal epilepsy (BFNE). The aim of this study was to identify PRRT2 mutations in infantile convulsions in Asian families with BFIE and ICCA, CwG and BFNE. Methods: We recruited 26 unrelated Japanese affected with either BFIE or non-familial benign infantile seizures and their families, including three families with ICCA. A total of 17 Japanese and Taiwanese with CwG, 50 Japanese with BFNE and 96 healthy volunteers were also recruited. Mutations of PRRT2 were sought using direct sequencing. Results: Heterozygous truncation mutation (c.649dupC) was identified in 15 of 26 individuals with benign infantile epilepsy (52.1%). All three families of ICCA harbored the same mutation (100%). Another novel mutation (c.1012+2dupT) was found in the proband of a family with BFIE. However, no PRRT2 mutation was found in either CwG or BFNE. Conclusions: The results confirm that c.649dupC, a truncating mutation of PRRT2, is a hotspot mutation resulting in BFIE or ICCA regardless of the ethnic background. In contrast, PRRT2 mutations do not seem to be associated with CwG or BFNE. Screening for PRRT2 mutation might be useful in early-stage differentiation of BFIE from CwG.     

Missense mutations of the proline-rich transmembrane protein 2 gene cosegregate with mild paroxysmal kinesigenic dyskinesia and infantile convulsions in a Chinese pedigree

Paroxysmal kinesigenic dyskinesia is an autosomal dominant dystonia induced by sudden voluntary movements. Recently, proline-rich transmembrane protein 2 (PRRT2) gene mutations, especially frameshift mutations, were described for PKD. In our study, we have collected a three-generation paroxysmal kinesigenic dyskinesia-infantile convulsions pedigree in Tianjin, North China. The symptoms of six patients varied; age of onset decreased in each generation. Mutations in the PRRT2 gene in nine PKD family members were screened by PCR sequencing of genomic DNA samples. Missense mutations of the PRRT2 gene were found in all four PKD patients and two children with infantile convulsions. All six individuals carried heterozygous codon 138 (Pro/Ala) and codon 306 (Ala/Asp) mutations. Missense mutations of the PRRT2 gene other than truncate and frameshift mutations were account for PKD and/or infantile convulsions. Age of onset and symptoms were not necessarily associated with PRRT2 mutations.     

Contactin‐associated protein‐like 2, a protein of the neurexin family involved in several human diseases

Contactin‐associated protein‐like 2 (CASPR2) is a cell adhesion protein of the neurexin family. Proteins of this family have been shown to play a role in the development of the nervous system, in synaptic functions, and in neurological diseases. Over recent years, CASPR2 function has gained an increasing interest as demonstrated by the growing number of publications. Here, we gather published data to comprehensively review CASPR2 functions within the nervous system in relation to CASPR2‐related diseases in humans. On the one hand, studies on Cntnap2 (coding for CASPR2) knockout mice revealed its role during development, especially, in setting‐up the inhibitory network. Consistent with this result, mutations in the CNTNAP2 gene coding for CASPR2 in human have been identified in neurodevelopmental disorders such as autism, intellectual disability, and epilepsy. On the other hand, CASPR2 was shown to play a role beyond development, in the localization of voltage‐gated potassium channel (VGKC) complex that is composed of TAG‐1, Kv1.1, and Kv1.2. This complex was found in several subcellular compartments essential for action potential propagation: the node of Ranvier, the axon initial segment, and the synapse. In line with a role of CASPR2 in the mature nervous system, neurological autoimmune diseases have been described in patients without neurodevelopmental disorders but with antibodies directed against CASPR2. These autoimmune diseases were of two types: central with memory disorders and temporal lobe seizures, or peripheral with muscular hyperactivity. Overall, we review the up‐to‐date knowledge on CASPR2 function and pinpoint confused or lacking information that will need further investigation.     

Loss of function mutations in ATP2A2 and psychoses: A case report and literature survey

Aim

Though genetic factors play a major role in the pathophysiology of psychoses including bipolar disorder (BD) and schizophrenia, lack of well‐established causative genetic mutations hampers their neurobiological studies. Darier's disease, an autosomal dominant skin disorder caused by mutations of ATP2A2 on chromosome 12q23‐24.1, encoding sarco/endoplasmic reticulum calcium transporting ATPase 2 (SERCA2), reportedly cosegregates with BD. A recent genome‐wide association study showed an association of schizophrenia with ATP2A2.

Methods

We sequenced all coding regions of ATP2A2 in a newly identified patient with Darier's disease and BD. In addition, we performed a literature survey to examine whether likely gene disrupting (LGD) mutations are related to psychoses.

Results

We identified a rare heterozygous mutation, c.1288‐6A>G, at the 3′ end of intron 10 in the patient. A minigene splicing assay showed that this mutation introduces a new splice site causing a frameshift and premature stop codon. A literature survey of case reports of patients with Darier's disease and psychoses revealed that the rate of LGD mutations causing frameshift, altered splicing, gain of stop codon, or loss of start codon was significantly higher among the mutations harbored by these cases (9 of 11) than that of ATP2A2 mutations for which comorbidity of psychosis was not reported (107 of 237, P = 0.026). The only non‐LGD mutation (p.C560R) reported in patients with Darier's disease and BD caused decreased ATP2A2 protein expression.

Conclusion

These results suggest that psychoses in Darier's disease may be caused by a pleiotropic effect of loss‐of‐function mutations of ATP2A2.     

Brain structural connectome in relation to PRRT2 mutations in paroxysmal kinesigenic dyskinesia

This study explored the topological characteristics of brain white matter structural networks in patients with Paroxysmal Kinesigenic Dyskinesia (PKD), and the potential influence of the brain network stability gene PRRT2 on the structural connectome in PKD. Thirty‐five PKD patients with PRRT2 mutations (PKD‐M), 43 PKD patients without PRRT2 mutations (PKD‐N), and 40 demographically‐matched healthy control (HC) subjects underwent diffusion tensor imaging. Graph theory and network‐based statistic (NBS) approaches were performed; the topological properties of the white matter structural connectome were compared across the groups, and their relationships with the clinical variables were assessed. Both disease groups PKD‐M and PKD‐N showed lower local efficiency (implying decreased segregation ability) compared to the HC group; PKD‐M had longer characteristic path length and lower global efficiency (implying decreased integration ability) compared to PKD‐N and HC, independently of the potential effects of medication. Both PKD‐M and PKD‐N had decreased nodal characteristics in the left thalamus and left inferior frontal gyrus, the alterations being more pronounced in PKD‐M patients, who also showed abnormalities in the left fusiform and bilateral middle temporal gyrus. In the connectivity characteristics assessed by NBS, the alterations were more pronounced in the PKD‐M group versus HC than in PKD‐N versus HC. As well as the white matter alterations in the basal ganglia‐thalamo‐cortical circuit related to PKD with or without PRRT2 mutations, findings in the PKD‐M group of weaker small‐worldness and more pronounced regional disturbance show the adverse effects of PRRT2 gene mutations on brain structural connectome.     

A cryptic splicing mutation in the INF2 gene causing Charcot‐Marie‐Tooth disease with minimal glomerular dysfunction

Heterozygous mutations in the inverted formin‐2 (INF2) gene provoke focal segmental glomerulosclerosis (FSGS) and intermediate Charcot‐Marie‐Tooth (CMT) disease with FSGS. Here, we report four patients from a three‐generation family with a new cryptic splicing INF2 mutation causing autosomal dominant intermediate CMT with minimal glomerular dysfunction. Three males and one female with a mean age of 51 years (26‐87) presented with a slowly progressive sensorimotor polyneuropathy, pes cavus, and kyphoscoliosis. Mean age at CMT disease onset was 11.5 years (3‐17), and electrophysiological studies showed demyelinating and axonal features consistent with intermediate CMT. Plasma albumin and creatinine were normal in all four cases, and urine protein was normal in one case and mildly raised in three patients (mean: 0.32 g/L [0.18‐0.44], N < 0.14). Genetic analysis found a c.271C > G (p. Arg91Gly) variation in INF2 exon 2, and in vitro splicing assays showed the deletion of the last 120 nucleotides of INF2 exon 2 leading to a 40 amino acids in‐frame deletion (p. Arg91_p. Gln130del). This report expands the genetic spectrum of INF2‐associated disorders and demonstrates that INF2 mutations may provoke isolated CMT with no clinically relevant kidney involvement. Consequently, INF2 mutation analysis should not be restricted to individuals with coincident neuropathy and renal disease.