Mutations in ACTL6B Cause Neurodevelopmental Deficits and Epilepsy and Lead to Loss of Dendrites in Human Neurons.

We identified individuals with variations in ACTL6B, a component of the chromatin remodeling machinery including the BAF complex. Ten individuals harbored bi-allelic mutations and presented with global developmental delay, epileptic encephalopathy, and spasticity, and ten individuals with de novo heterozygous mutations displayed intellectual disability, ambulation deficits, severe language impairment, hypotonia, Rett-like stereotypies, and minor facial dysmorphisms (wide mouth, diastema, bulbous nose). Nine of these ten unrelated individuals had the identical de novo c.1027G>A (p.Gly343Arg) mutation. Human-derived neurons were generated that recaptured ACTL6B expression patterns in development from progenitor cell to post-mitotic neuron, validating the use of this model. Engineered knock-out of ACTL6B in wild-type human neurons resulted in profound deficits in dendrite development, a result recapitulated in two individuals with different bi-allelic mutations, and reversed on clonal genetic repair or exogenous expression of ACTL6B. Whole-transcriptome analyses and whole-genomic profiling of the BAF complex in wild-type and bi-allelic mutant ACTL6B neural progenitor cells and neurons revealed increased genomic binding of the BAF complex in ACTL6B mutants, with corresponding transcriptional changes in several genes including TPPP and FSCN1, suggesting that altered regulation of some cytoskeletal genes contribute to altered dendrite development. Assessment of bi-alleic and heterozygous ACTL6B mutations on an ACTL6B knock-out human background demonstrated that bi-allelic mutations mimic engineered deletion deficits while heterozygous mutations do not, suggesting that the former are loss of function and the latter are gain of function. These results reveal a role for ACTL6B in neurodevelopment and implicate another component of chromatin remodeling machinery in brain disease.

Mutations in RPSA and NKX2-3 link development of the spleen and intestinal vasculature.

Idiopathic intestinal varicosis is a developmental disorder defined by dilated and convoluted submucosal veins in the colon or small bowel. A limited number of families with idiopathic intestinal varices has been reported, but the genetic cause has not yet been identified. We performed whole-exome and targeted Sanger sequencing of candidate genes in five intestinal varicosis families. In four families, mutations in the RPSA gene were found, a gene previously linked to congenital asplenia. Individuals in these pedigrees had intestinal varicose veins and angiodysplasia, often in combination with asplenia. In a further four-generation pedigree that only showed intestinal varicosities, the RPSA gene was normal. Instead, a nonsense mutation in the homeobox gene NKX2-3 was detected which cosegregated with the disease in this large family with a LOD (logarithm of the odds) score of 3.3. NKX2-3 is a component of a molecular pathway underlying spleen and gut vasculature development in mice. Our results provide a molecular basis for familial idiopathic intestinal varices. We provide evidence for a relationship between the molecular pathways underlying the development of the spleen and intestinal mucosal vasculature that is conserved between humans and mice. We propose that clinical management of intestinal varices, should include assessment of a functional spleen.

Segregation analysis in families with Charcot-Marie-Tooth disease allows reclassification of putative disease causing mutations.

BACKGROUND: The identification of disease causing, or putative disease causing, mutations in index patients with Charcot-Marie-Tooth disease (CMT) allows for genetic testing of family members. Relevant variants identified in index patients are of either definite, likely or uncertain pathogenicity. The main objective of this study was to make an evaluation of the family investigations performed as part of the assessment of genetic variants of unknown clinical significance (VUS). METHODS: Between 2004 and 2010 molecular genetic family investigations were requested for 87 family members from 41 families harbouring PMP22dup or genetic variants in GJB1, MPZ, MFN2 and NEFL. Relatives were tested for the family mutation and data from the requisitions were evaluated by means of statistical tools. RESULTS: The results within each indication category are presented and discussed in detail. Twenty-two relatives (9 affected) from eight families were included in the segregation analyses, which invoked reclassification of three MFN2 mutations, two of which were de novo substitutions (c.2146_2148dup, c.692C > T). One MFN2 substitution was downgraded due to non-segregation (c.1709 A > G), and a MPZ substitution (c.103 G > A) upgraded due to segregation with the phenotype in the family. CONCLUSIONS: The results allow for the evaluation of the patient phenotypes ascertained in families, as opposed to the phenotypic descriptions of index patients. They indicate that de novo MFN2 mutations are regularly found in patients with a classical CMT2 phenotype. They also demonstrate the importance of a precise clinical and neurophysiologic diagnosis of affected family members. This particularly applies for the examination of variants of uncertain clinical significance. Finally, the fact that 14,6% of affected relatives tested for (probable or certain) pathogenic mutations were mutation negative, demonstrates that clinical evaluation alone is not always sufficient in order to determine their diagnosis. We believe that the results will aid in the estimation and planning of resources required for the various aspects of family evaluations in CMT.

Diagnostic laboratory testing for Charcot Marie Tooth disease (CMT): the spectrum of gene defects in Norwegian patients with CMT and its implications for future genetic test strategies.

BACKGROUND: Current genetic test algorithms for Charcot Marie Tooth (CMT) disease are based on family details and comprehensive clinical and neurophysiological data gathered under ideal conditions for clinical assessment. However, in a diagnostic laboratory setting relying on external test requisitions and patient samples, such conditions are not always met. Our objective was therefore to perform a retrospective evaluation of the data given in laboratory request forms and to assess their quality and applicability with regard to the recommended algorithms for CMT diagnostics. As we are the main test centre for CMT in Norway our results also provide an overview of the spectrum of gene defects in the Norwegian CMT population. METHODS: Genetic testing was performed according to polyneuropathy type; demyelinating/mixed: PMP22 duplication, MPZ, EGR2, LITAF, NEFL, PMP22, GJB1, axonal: MFN2, MPZ, NEFL, and GJB1. RESULTS: Diagnostic testing of index patients was requested in 435 of the 549 cases. Seventy-two (16.6%) positive molecular genetic findings were made. The majority (94.6%) of mutation positive cases showed disease onset before 50 years of age. PMP22 (duplication), MPZ, GJB1 and MFN2 mutations constituted 95.8% of the positive findings. Within the nerve conduction study groups, mutation detection rates were; demyelinating 33.8%; mixed 29.0%; axonal 8.8%; unspecified 16.5%. CONCLUSION: We suggest a simplified algorithm intended for referral centres, dealing with DNA/blood samples, which involves the assessment of age at onset and neurophysiological data followed by testing of four genes; PMP22 (duplication), MPZ, GJB1 and MFN2. Patients negative for mutations in those four genes should be subjected to evaluation at an interdisciplinary inherited neuropathy clinic with the capacity for extended molecular genetic analysis by next generation sequencing.

Börjeson-Forssman-Lehmann syndrome: delineating the clinical and allelic spectrum in 14 new families.

Börjeson-Forssman-Lehmann syndrome (BFLS) is an X-linked intellectual disability syndrome caused by variants in the PHF6 gene. We ascertained 19 individuals from 15 families with likely pathogenic or pathogenic PHF6 variants (11 males and 8 females). One family had previously been reported. Six variants were novel. We analysed the clinical and genetic findings in our series and compared them with reported BFLS patients. Affected males had classic features of BFLS including intellectual disability, distinctive facies, large ears, gynaecomastia, hypogonadism and truncal obesity. Carrier female relatives of affected males were unaffected or had only mild symptoms. The phenotype of affected females with de novo variants overlapped with the males but included linear skin hyperpigmentation and a higher frequency of dental, retinal and cortical brain anomalies. Complications observed in our series included keloid scarring, digital fibromas, absent vaginal orifice, neuropathy, umbilical hernias, and talipes. Our analysis highlighted sex-specific differences in PHF6 variant types and locations. Affected males often have missense variants or small in-frame deletions while affected females tend to have truncating variants or large deletions/duplications. Missense variants were found in a minority of affected females and clustered in the highly constrained PHD2 domain of PHF6. We propose recommendations for the evaluation and management of BFLS patients. These results further delineate and extend the genetic and phenotypic spectrum of BFLS.

Charcot-Marie-Tooth disease type 4C in Norway: Clinical characteristics, mutation spectrum and minimum prevalence.

Autosomal recessive Charcot-Marie-Tooth disease (CMT) is considered rare and phenotypic descriptions are scarce for the different subgroups. Mutations in the SH3TC2 gene, causing recessive demyelinating CMT type 4C have been found in several Norwegian CMT patients over the last years. We aimed to estimate a minimum prevalence and to study the genotypic and phenotypic variability of CMT4C in Norway. Patients were selected from diagnostic registries in medical genetic centers in Norway for cases of CMT4C. All patients were invited to complete a questionnaire and give medical consent to the use of clinical data from medical hospital records. A total of 35 patients from 31 families were found with CMT4C, which gives a minimum prevalence of 0.7/100,000 in Norway. Six new mutations were identified. Most patients had debut in the first decade with foot deformities, distal limb paresis, sensory ataxia and scoliosis. Proximal lower limb paresis and cranial nerve involvement was seen in about half of the patients. CMT4C is the most common recessive CMT in Norway. In addition to the classic distal limb affection, early debut, scoliosis, proximal paresis, cranial nerve affection and sensory ataxia are the most prominent features of CMT4C.

Hereditary motor neuron disease in a large Norwegian family with a "H46R" substitution in the superoxide dismutase 1 gene.

Mutant genes associated with Charcot Marie Tooth type 2, distal hereditary motor neuropathy and familial amyotrophic lateral sclerosis may cause overlapping clinical phenotypes. We performed whole genome linkage analysis, haplotype analysis, sequencing and detailed clinical and neurophysiological investigations in a large Norwegian kindred with a condition that clinically had been classified as Charcot Marie Tooth type 2. The mutation c.140A>G, p.His47Arg (alias p.His46Arg or H46R) in the superoxide dismutase 1 gene (SOD1) segregated with the disease. The patients present a hereditary motor neuropathy-like clinical picture and long survival (mean 29years). To our knowledge, this is the first extensive report describing a large non-Japanese kindred. The prognostic implications of the condition seen in this family have little in common with what is normally associated with sporadic amyotrophic lateral sclerosis and illustrates the complexity of the genetic etiology of lower motor neuron disease.