We previously localized a new form of recessive ataxia with generalized tonic-clonic epilepsy and mental retardation to a 19 Mb interval in 16q21-q23 by homozygosity mapping of a large consanguineous Saudi Arabian family. We now report the identification by whole exome sequencing of the missense mutation changing proline 47 into threonine in the first WW domain of the WW domain containing oxidoreductase gene, WWOX, located in the linkage interval. Proline 47 is a highly conserved residue that is part of the WW motif consensus sequence and is part of the hydrophobic core that stabilizes the WW fold. We demonstrate that proline 47 is a key amino acid essential for maintaining the WWOX protein fully functional, with its mutation into a threonine resulting in a loss of peptide interaction for the first WW domain. We also identified another highly conserved homozygous WWOX mutation changing glycine 372 to arginine in a second consanguineous family. The phenotype closely resembled the index family, presenting with generalized tonic-clonic epilepsy, mental retardation and ataxia, but also included prominent upper motor neuron disease. Moreover, we observed that the short-lived Wwox knock-out mouse display spontaneous and audiogenic seizures, a phenotype previously observed in the spontaneous Wwox mutant rat presenting with ataxia and epilepsy, indicating that homozygous WWOX mutations in different species causes cerebellar ataxia associated with epilepsy.

Despite extensive efforts, half of patients with rare movement disorders such as hereditary spastic paraplegias and cerebellar ataxias remain genetically unexplained, implicating novel genes and unrecognized mutations in known genes. Non-coding DNA variants are suspected to account for a substantial part of undiscovered causes of rare diseases. Here we identified mutations located deep in introns of POLR3A to be a frequent cause of hereditary spastic paraplegia and cerebellar ataxia. First, whole-exome sequencing findings in a recessive spastic ataxia family turned our attention to intronic variants in POLR3A, a gene previously associated with hypomyelinating leukodystrophy type 7. Next, we screened a cohort of hereditary spastic paraplegia and cerebellar ataxia cases (n = 618) for mutations in POLR3A and identified compound heterozygous POLR3A mutations in ∼3.1% of index cases. Interestingly, >80% of POLR3A mutation carriers presented the same deep-intronic mutation (c.1909+22G>A), which activates a cryptic splice site in a tissue and stage of development-specific manner and leads to a novel distinct and uniform phenotype. The phenotype is characterized by adolescent-onset progressive spastic ataxia with frequent occurrence of tremor, involvement of the central sensory tracts and dental problems (hypodontia, early onset of severe and aggressive periodontal disease). Instead of the typical hypomyelination magnetic resonance imaging pattern associated with classical POLR3A mutations, cases carrying c.1909+22G>A demonstrated hyperintensities along the superior cerebellar peduncles. These hyperintensities may represent the structural correlate to the cerebellar symptoms observed in these patients. The associated c.1909+22G>A variant was significantly enriched in 1139 cases with spastic ataxia-related phenotypes as compared to unrelated neurological and non-neurological phenotypes and healthy controls (P = 1.3 × 10-4). In this study we demonstrate that (i) autosomal-recessive mutations in POLR3A are a frequent cause of hereditary spastic ataxias, accounting for about 3% of hitherto genetically unclassified autosomal recessive and sporadic cases; and (ii) hypomyelination is frequently absent in POLR3A-related syndromes, especially when intronic mutations are present, and thus can no longer be considered as the unifying feature of POLR3A disease. Furthermore, our results demonstrate that substantial progress in revealing the causes of Mendelian diseases can be made by exploring the non-coding sequences of the human genome.

Mitochondrial chaperonins are necessary for the folding of newly imported and stress-denatured mitochondrial proteins. The goal of this study was to investigate the structure and function of the mammalian mitochondrial chaperonin system. We present evidence that the 60 kDa chaperonin (mt-cpn60) exists in solution in dynamic equilibrium between monomers, heptameric single rings and doubleringed tetradecamers. In the presence of ATP and the 10 kDa cochaperonin (mt-cpn10), the formation of a double ring is favored. ADP at very high concentrations does not inhibit malate dehydrogenase refolding or ATP hydrolysis by mt-cpn60 in the presence of mt-cpn10. We propose that the cis (mt-cpn60) 14´n uleotide´(mt-cpn10) 7 complex is not a stable species and does not bind ADP effectively at its trans binding site.Keywords: chaperonin; mitochondrial folding; cpn60; cpn10; hsp60.The 60 kDa chaperonins constitute a highly conserved family of proteins found in chloroplasts, mitochondria and eubacteria, which plays an important role in the folding of nascent, translocating and stress-denatured proteins [1]. In yeast mitochondria, chaperonins mediate the folding of both newly imported and stress-denatured proteins, and are essential for the viability of yeast under all conditions [2±5]. Consistent with such an important role, numerous studies have found altered levels of mammalian mitochondrial chaperonin 60 (mt-cpn60) associated with various pathological states [6±11]. Despite the importance of this molecule, few studies have been carried out to understand the details of mammalian mt-cpn60 structure and function. Due to the high level of homology at both the sequence level and functional level, it was commonly assumed that mt-cpn60 was mechanistically similar to its well-studied bacterial counterpart, GroEL. Indeed, the mitochondrial chaperonin system can fold denatured proteins in vitro, with a similar efficiency to GroEL [12,13], and is able to replace the bacterial GroEL in Escherichia coli in vivo [14]. However, a number of significant differences have been reported in the structure of mt-cpn60, which suggest that this eucaryotic chaperonin may have developed a different mechanism of action. While all other chaperonin homologs exist as tetradecamers composed of two seven-membered rings, the mammalian mt-cpn60 has been consistently isolated as a single ring [12,13]. Moreover, mt-cpn60 readily dissociates to monomers in the presence of ATP, low temperatures, and the nonphysiological concentrations that are routinely used for in vitro studies [15]. The functional significance of such instability is unclear. One other interesting difference lies in the fact that mitochondrial cpn60s are functional only with their own 10 kDa cofactor, mitochondrial chaperonin 10 (mt-cpn10) [12,15], whereas the bacterial and chloroplast cpn60 can fold proteins with cpn10 from any source [12,13,16±18].Numerous mechanistic studies over the past decade have resulted in a putative mechanism of action for the GroEL chaperonin [19]. Central to this mechan...

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The prevalence of consanguinity within the Israeli Arab community is relatively high, and is associated with high rates of inherited disorders that lead to a high frequency of morbidity and mortality. Data on consanguinity between couples were recorded during two periods (1980-1985 and 2000-2004) in relation to socioeconomic status of 4 selected villages. Two of the villages (A and B) are known to have high socioeconomic status, and the other two (C and D) are known to have low socioeconomic status. The average incidence of consanguineous marriages has slightly decreased from 33.1% in the first period to 25.9% in the second period (P = 0.0218) in all of the 4 villages. Marriages between first cousins showed a more significant decrease, from 23.9% in the first period to 13.6% in the second period (P < 0.0001). The average consanguinity rates of villages A and B were found to decrease from 22.3 to 16.2% respectively (P < 0.001) between the two observation periods, whereas those of villages C and D were found to decrease from 42.3 to 37.2%, (P < 0.001) during the same two periods. Thus, there has been a change in the pattern of consanguinity within the selected Israeli Arab villages, between the two study periods. This change seems to correlate with the sociodemographic status of the villages. Therefore, improving the socioeconomic status of the villages, as well as implementation of proper health education programs, is expected to have a positive effect in reducing consanguinity.

Objective:To explore the phenotypic spectrum and pathophysiology of human disease deriving from mutations in the CNTNAP1 gene.Methods:In a field study on consanguineous Palestinian families, we identified 3 patients carrying homozygous mutations in the CNTNAP1 gene using whole-exome sequencing. An unrelated Irish family was detected by screening the GENESIS database for further CNTNAP1 mutations. Neurophysiology, MRI, and nerve biopsy including electron microscopy were performed for deep phenotyping.Results:We identified 3 novel CNTNAP1 mutations in 5 patients from 2 families: c.2015G>A:p.(Trp672*) in a homozygous state in family 1 and c.2011C>T:p.(Gln671*) in a compound heterozygous state with c.2290C>T:p.(Arg764Cys) in family 2. Affected patients suffered from a severe CNS disorder with hypomyelinating leukodystrophy and peripheral neuropathy of sensory-motor type. Arthrogryposis was present in 2 patients but absent in 3 patients. Brain MRI demonstrated severe hypomyelination and secondary cerebral and cerebellar atrophy as well as a mega cisterna magna and corpus callosum hypoplasia. Nerve biopsy revealed very distinct features with lack of transverse bands at the paranodes and widened paranodal junctional gaps.Conclusions:CNTNAP1 mutations have recently been linked to patients with arthrogryposis multiplex congenita. However, we show that arthrogryposis is not an obligate feature. CNTNAP1-related disorders are foremost severe hypomyelinating disorders of the CNS and the peripheral nervous system. The pathology is partly explained by the involvement of CNTNAP1 in the proper formation and preservation of paranodal junctions and partly by the assumed role of CNTNAP1 as a key regulator in the development of the cerebral cortex.

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In this study, we have investigated the relationship between chaperonin/co-chaperonin binding, ATP hydrolysis, and protein refolding in heterologous chaperonin systems from bacteria, chloroplast, and mitochondria. We characterized two types of chloroplast cpn60 oligomers, ch-cpn60 composed of alpha and beta subunits (alpha(7)beta(7) ch-cpn60) and one composed of all beta subunits (beta(14) ch-cpn60). In terms of ATPase activity, the rate of ATP hydrolysis increased with protein concentration up to 60 microM, reflecting a concentration at which the oligomers are stable. At high concentrations of cpn60, all cpn10 homologs inhibited ATPase activity of alpha(7)beta(7) ch-cpn60. In contrast, ATPase of beta(14) ch-cpn60 was inhibited only by mitochondrial cpn10, supporting previous reports showing that beta(14) is functional only with mitochondrial cpn10 and not with other cpn10 homologs. Surprisingly, direct binding assays showed that both ch-cpn60 oligomer types bind to bacterial, mitochondrial, and chloroplast cpn10 homologs with an equal apparent affinity. Moreover, mitochondrial cpn60 binds chloroplast cpn20 with which it is not able to refold denatured proteins. Protein refolding experiments showed that in such instances, the bound protein is released in a conformation that is not able to refold. The presence of glycerol, or subsequent addition of mitochondrial cpn10, allows us to recover enzymatic activity of the substrate protein. Thus, in our systems, the formation of co-chaperonin/chaperonin complexes does not necessarily lead to protein folding. By using heterologous oligomer systems, we are able to separate the functions of binding and refolding in order to better understand the chaperonin mechanism.