A truncating mutation in CEP55 is the likely cause of MARCH, a novel syndrome affecting neuronal mitosis.

BACKGROUND: Hydranencephaly is a congenital anomaly leading to replacement of the cerebral hemispheres with a fluid-filled cyst. The goals of this work are to describe a novel autosomal-recessive syndrome that includes hydranencephaly (multinucleated neurons, anhydramnios, renal dysplasia, cerebellar hypoplasia and hydranencephaly (MARCH)); to identify its genetic cause(s) and to provide functional insight into pathomechanism. METHODS: We used homozygosity mapping and exome sequencing to identify recessive mutations in a single family with three affected fetuses. Immunohistochemistry, RT-PCR and imaging in cell lines, and zebrafish models, were used to explore the function of the gene and the effect of the mutation. RESULTS: We identified a homozygous nonsense mutation in CEP55 segregating with MARCH. Testing the effect of this allele on patient-derived cells indicated both a reduction of the overall CEP55 message and the production of a message that likely gives rise to a truncated protein. Suppression or ablation of cep55l in zebrafish embryos recapitulated key features of MARCH, most notably renal dysplasia, cerebellar hypoplasia and craniofacial abnormalities. These phenotypes could be rescued by full-length but not truncated human CEP55 message. Finally, we expressed the truncated form of CEP55 in human cells, where we observed a failure of truncated protein to localise to the midbody, leading to abscission failure and multinucleated daughter cells. CONCLUSIONS: CEP55 loss of function mutations likely underlie MARCH, a novel multiple congenital anomaly syndrome. This association expands the involvement of centrosomal proteins in human genetic disorders by highlighting a role in midbody function.

Protective effects of butyrate-based compounds on a mouse model for spinal muscular atrophy.

Proximal spinal muscular atrophy (SMA) is a childhood-onset degenerative disease resulting from the selective loss of motor neurons in the spinal cord. SMA is caused by the loss of SMN1 (survival motor neuron 1) but retention of SMN2. The number of copies of SMN2 modifies disease severity in SMA patients as well as in mouse models, making SMN2 a target for therapeutics development. Sodium butyrate (BA) and its analog (4PBA) have been shown to increase SMN2 expression in SMA cultured cells. In this study, we examined the effects of BA, 4PBA as well as two BA prodrugs-glyceryl tributyrate (BA3G) and VX563-on the phenotype of SMNΔ7 SMA mice. Treatment with 4PBA, BA3G and VX563 but not BA beginning at PND04 significantly improved the lifespan and delayed disease end stage, with administration of VX563 also improving the growth rate of these mice. 4PBA and VX563 improved the motor phenotype of SMNΔ7 SMA mice and prevented spinal motor neuron loss. Interestingly, neither 4PBA nor VX563 had an effect on SMN expression in the spinal cords of treated SMNΔ7 SMA mice; however, they inhibited histone deacetylase (HDAC) activity and restored the normal phosphorylation states of Akt and glycogen synthase kinase 3ß, both of which are altered by SMN deficiency in vivo. These observations show that BA-based compounds with favorable pharmacokinetics ameliorate SMA pathology possibly by modulating HDAC and Akt signaling.

A novel CCBE1 mutation leading to a mild form of hennekam syndrome: case report and review of the literature.

BACKGROUND: Mutations in CCBE1 have been found to be responsible for a subset of families with autosomal recessive Hennekam syndrome. Hennekam syndrome is defined as the combination of generalized lymphatic dysplasia (ie. lymphedema and lymphangiectasia), variable intellectual disability and characteristic dysmorphic features. The patient we describe here has a lymphatic dysplasia without intellectual disability or dysmorphism caused by mutation in CCBE1, highlighting the phenotypic variability that can be seen with abnormalities in this gene. CASE PRESENTATION: Our patient is a 5 week old child of Pakistani descent who presented to our center with generalized edema, ascites, and hypoalbuminemia. She was diagnosed with a protein losing enteropathy secondary to segmental primary intestinal lymphangiectasia. As the generalized edema resolved, it became clear that she had mild persistent lymphedema in her hands and feet. No other abnormalities were noted on examination and development was unremarkable at 27 months of age. Given the suspected genetic etiology and the consanguinity in the family, we used a combination of SNP genotyping and exome sequencing to identify the underlying cause of her disease. We identified several large stretches of homozygosity in the patient that allowed us to sort the variants found in the patient's exome to identify p.C98W in CCBE1 as the likely pathogenic variant. CONCLUSIONS: CCBE1 mutation analysis should be considered in all patients with unexplained lymphatic dysplasia even without the other features of classic Hennekam syndrome.

A novel mutation in KIAA0196: identification of a gene involved in Ritscher-Schinzel/3C syndrome in a First Nations cohort.

BACKGROUND: Ritscher-Schinzel syndrome (RSS) is a clinically heterogeneous disorder characterised by distinctive craniofacial features in addition to cerebellar and cardiac anomalies. It has been described in different populations and is presumed to follow autosomal recessive inheritance. In an effort to identify the underlying genetic cause of RSS, affected individuals from a First Nations (FN) community in northern Manitoba, Canada, were enrolled in this study. METHODS: Homozygosity mapping by SNP array and Sanger sequencing of the candidate genes in a 1Mb interval on chromosome 8q24.13 were performed on genomic DNA from eight FN RSS patients, eight of their parents and five unaffected individuals (control subjects) from this geographic isolate. RESULTS: All eight patients were homozygous for a novel splice site mutation in KIAA0196. RNA analysis revealed an approximate eightfold reduction in the relative amount of a KIAA0196 transcript lacking exon 27. A 60% reduction in the amount of strumpellin protein was observed on western blot. CONCLUSIONS: We have identified a mutation in KIAA0196 as the cause of the form of RSS characterised in our cohort. The ubiquitous expression and highly conserved nature of strumpellin, the product of KIAA0196, is consistent with the complex and multisystem nature of this disorder.

A newborn with spinal muscular atrophy type 0 presenting with a clinicopathological picture suggestive of myotubular myopathy.

We report a male term newborn with genetically confirmed spinal muscular atrophy type 0, presenting with arthrogryposis and severe generalized weakness and requiring ventilatory support. Muscle biopsy revealed fibers with central nuclei resembling myotubes and negative myotubularin immunohistochemical staining compared with a control muscle biopsy. The absence of myotubularin associated with survival motor neuron protein deficiency suggests that survival motor neuron protein may have a role in muscle fiber maturation and myotubularin expression. Studying the pathology of this rare and lethal neonatal form of spinal muscular atrophy may further our understanding of spinal muscular atrophy pathogenesis.

Survival motor neuron (SMN) protein: role in neurite outgrowth and neuromuscular maturation during neuronal differentiation and development.

Childhood spinal muscular atrophy (SMA) is a common neuromuscular disorder caused by absent or deficient full-length survival motor neuron (SMN) protein. Clinical studies and animal models suggest that SMA is a developmental defect in neuromuscular interaction; however, the role of SMN in this process remains unclear. In the present study, we have determined the subcellular localization of SMN during retinoic-acid-induced neuronal differentiation of mouse embryonal teratocarcinoma P19 cells as well as in skeletal muscle during the critical period of neuromuscular maturation. We demonstrate, for the first time, SMN accumulation in growth-cone- and filopodia-like structures in both neuronal- and glial-like cells, identifying SMN as a new growth cone marker. Indeed, SMN was present at the leading edge of neurite outgrowths, suggesting that SMN may play a role in this process. In addition, SMN was detected as small dot-like particles within the cytoplasm of skeletal muscle during the first 2 weeks after birth, but their number peaked by P6. Intense SMN staining in neuromuscular junctions was observed throughout the entire postnatal period examined. Taken together, these results suggest that SMN may indeed fulfill neuronal- and muscle-specific functions, providing a more plausible mechanism explaining motor neuron degeneration and associated denervation atrophy of skeletal muscles in SMA. The primary SMA pathology most likely initiates in the peripheral axon--the result of deficient neurite outgrowth and/or neuromuscular maturation.