Mutations in Subunits of the Activating Signal Cointegrator 1 Complex Are Associated with Prenatal Spinal Muscular Atrophy and Congenital Bone Fractures.

Transcriptional signal cointegrators associate with transcription factors or nuclear receptors and coregulate tissue-specific gene transcription. We report on recessive loss-of-function mutations in two genes (TRIP4 and ASCC1) that encode subunits of the nuclear activating signal cointegrator 1 (ASC-1) complex. We used autozygosity mapping and whole-exome sequencing to search for pathogenic mutations in four families. Affected individuals presented with prenatal-onset spinal muscular atrophy (SMA), multiple congenital contractures (arthrogryposis multiplex congenita), respiratory distress, and congenital bone fractures. We identified homozygous and compound-heterozygous nonsense and frameshift TRIP4 and ASCC1 mutations that led to a truncation or the entire absence of the respective proteins and cosegregated with the disease phenotype. Trip4 and Ascc1 have identical expression patterns in 17.5-day-old mouse embryos with high expression levels in the spinal cord, brain, paraspinal ganglia, thyroid, and submandibular glands. Antisense morpholino-mediated knockdown of either trip4 or ascc1 in zebrafish disrupted the highly patterned and coordinated process of α-motoneuron outgrowth and formation of myotomes and neuromuscular junctions and led to a swimming defect in the larvae. Immunoprecipitation of the ASC-1 complex consistently copurified cysteine and glycine rich protein 1 (CSRP1), a transcriptional cofactor, which is known to be involved in spinal cord regeneration upon injury in adult zebrafish. ASCC1 mutant fibroblasts downregulated genes associated with neurogenesis, neuronal migration, and pathfinding (SERPINF1, DAB1, SEMA3D, SEMA3A), as well as with bone development (TNFRSF11B, RASSF2, STC1). Our findings indicate that the dysfunction of a transcriptional coactivator complex can result in a clinical syndrome affecting the neuromuscular system.

Recessive DEAF1 mutation associates with autism, intellectual disability, basal ganglia dysfunction and epilepsy.

BACKGROUND: Various genetic defects cause autism associated with intellectual disability and epilepsy. Here, we set out to identify the genetic defect in a consanguineous Omani family with three affected children in whom mutations in known candidate genes had been excluded beforehand. METHODS: For mutation screening, we combined autozygosity mapping and whole exome sequencing. Segregation of potential disease variants with the phenotype was verified by Sanger sequencing. A splice-site mutation was confirmed and quantified by qPCR. RESULTS: We found an autosomal recessive splice acceptor mutation in DEAF1 (c.997+4A>C, p.G292Pfs*) in all affected individuals, which led to exon skipping, and reduced the normal full-length mRNA copy number in the patients to 5% of the wild-type level. Besides intellectual disability and autism, two of three affected siblings suffered from severe epilepsy. All patients exhibited dyskinesia of the limbs coinciding with symmetric T2 hyperintensities of the basal ganglia on cranial MRI. CONCLUSIONS: A recent report has shown dominant DEAF1 mutations to occur de novo in patients with intellectual disability. Here, we demonstrate that a DEAF1-associated disorder can also be inherited as an autosomal recessive trait with heterozygous individuals being entirely healthy. Our findings expand the clinical and genetic spectrum of DEAF1 mutations to comprise epilepsy and extrapyramidal symptoms.

Regionalized pathology correlates with augmentation of mtDNA copy numbers in a patient with myoclonic epilepsy with ragged-red fibers (MERRF-syndrome).

Human patients with myoclonic epilepsy with ragged-red fibers (MERRF) suffer from regionalized pathology caused by a mutation in the mitochondrial DNA (m.8344A→G). In MERRF-syndrome brain and skeletal muscles are predominantly affected, despite mtDNA being present in any tissue. In the past such tissue-specificity could not be explained by varying mtDNA mutation loads. In search for a region-specific pathology in human individuals we determined the mtDNA/nDNA ratios along with the mutation loads in 43 different post mortem tissue samples of a 16-year-old female MERRF patient and in four previously healthy victims of motor vehicle accidents. In brain and muscle we further determined the quantity of mitochondrial proteins (COX subunits II and IV), transcription factors (NRF1 and TFAM), and VDAC1 (Porin) as a marker for the mitochondrial mass. In the patient the mutation loads varied merely between 89-100%. However, mtDNA copy numbers were increased 3-7 fold in predominantly affected brain areas (e.g. hippocampus, cortex and putamen) and in skeletal muscle. Similar increases were absent in unaffected tissues (e.g. heart, lung, kidney, liver, and gastrointestinal organs). Such mtDNA copy number increase was not paralleled by an augmentation of mitochondrial mass in some investigated tissues, predominantly in the most affected tissue regions of the brain. We thus conclude that "futile" stimulation of mtDNA replication per se or a secondary failure to increase the mitochondrial mass may contribute to the regionalized pathology seen in MERRF-syndrome.

Many roads lead to primary autosomal recessive microcephaly.

Autosomal recessive primary microcephaly (MCPH), historically referred to as Microcephalia vera, is a genetically and clinically heterogeneous disease. Patients with MCPH typically exhibit congenital microcephaly as well as mental retardation, but usually no further neurological findings or malformations. Their microcephaly with grossly preserved macroscopic organization of the brain is a consequence of a reduced brain volume, which is evident particularly within the cerebral cortex and thus results to a large part from a reduction of grey matter. Some patients with MCPH further provide evidence of neuronal heterotopias, polymicrogyria or cortical dysplasia suggesting an associated neuronal migration defect. Genetic causes of MCPH subtypes 1-7 include mutations in genes encoding microcephalin, cyclin-dependent kinase 5 regulatory associated protein 2 (CDK5RAP2), abnormal spindle-like, microcephaly associated protein (ASPM), centromeric protein J (CENPJ), and SCL/TAL1-interrupting locus (STIL) as well as linkage to the two loci 19q13.1-13.2 and 15q15-q21. Here, we provide a timely overview of current knowledge on mechanisms leading to microcephaly in humans with MCPH and abnormalities in cell division/cell survival in corresponding animal models. Understanding the pathomechanisms leading to MCPH is of high importance not only for our understanding of physiologic brain development (particularly of cortex formation), but also for that of trends in mammalian evolution with a massive increase in size of the cerebral cortex in primates, of microcephalies of other etiologies including environmentally induced microcephalies, and of cancer formation.

Increased mRNA expression of tissue inhibitors of metalloproteinase-1 and -2 in Duchenne muscular dystrophy.

In dystrophinopathies, disease severity is generally related to the extent of muscle fibrosis. To determine whether a decrease in matrix degradation contributes to the severe fibrosis seen in Duchenne muscular dystrophy (DMD), we quantified RNA transcript numbers for the fibrolytic matrix metalloproteinases (MMP)-1 and -2 and their natural tissue inhibitors (TIMP)-1 and -2 in DMD muscle as well as in pathological and normal controls. In addition, we investigated gelatinase (MMP-2) enzyme activity by zymography. We found an up-regulation of TIMP-1, TIMP-2 and MMP-2 RNA in DMD muscle. Zymography revealed an increase in MMP-2 activity in DMD muscle homogenates, which was absent in pathological and normal controls. Therefore, besides enhanced fibrogenesis, a disturbance of matrix degradation may play a significant role in muscle fibrosis in DMD. TIMP-1 should be investigated further as a promising target for pharmacological intervention to prevent muscle fibrosis in DMD.