Markus Schuelke

An economic method for the fluorescent labeling of PCR fragments

A poor mans approach to genotyping for research and high-throughput diagnostics.

MutationTaster evaluates disease-causing potential of sequence alterations

(simple_aae) or at alterations causing complex changes in the amino acid sequence (complex_aae). To train the classifier, we generated a dataset with all available and suitable common polymorphisms and known diseasecausing mutations extracted from common databases and the literature. We cross-validated the classifier five times including all three prediction models and obtained an overall accuracy of 91.1 ± 0.1%. We also compared MutationTaster with similar applications (Panther3, Pmut4, PolyPhen and PolyPhen-2 (ref. 5) and ‘screening for non-acceptable polymorphisms’ (SNAP)6) and analyzed the identical 1,000 disease-linked mutations and 1,000 polymorphisms with all programs. For this comparison, we used only alterations causing single amino acid exchanges. MutationTaster performed best in terms of accuracy and speed (Table 1). A description of all training and validation procedures and detailed statistics are available in Supplementary Methods. MutationTaster can be used via an intuitive web interface to analyze single mutations as well as in batch mode. To streamline and to standardize the analysis of NGS data, we provide Perl scripts that can process data from all major platforms (Roche 454, Illumina Genome Analyzer and ABI SOLiD). MutationTaster hence allows the efficient filtering of NGS data for alterations with high disease-causing potential (see Supplementary Methods for an example). Present limitations of the software comprise its inability to analyze insertion-deletions greater than 12 base pairs and alterations spanning an intron-exon border. Also, analysis of non-exonic alterations is restricted to Kozak consensus sequence, splice sites and poly(A) signal. We will add tests for other sequence motifs in the near future. MutationTaster is available at http://www.mutationtaster.org/.

MutationTaster2: mutation prediction for the deep-sequencing age

To the Editor: The majority of the gene variants discovered by nextgeneration sequencing (NGS) projects are either intronic or synonymous. These variants are difficult to interpret because their effects on protein expression and function tend to be less obvious than those of missense or nonsense variants. Here we present MutationTaster2 (http://www.mutationtaster.org/), the latest version of our web-based software MutationTaster1, which evaluates the pathogenic potential of DNA sequence alterations. It is designed to predict the functional consequences of not only amino acid substitutions but also intronic and synonymous alterations, short insertion and/or deletion (indel) mutations and variants spanning intron-exon borders. MutationTaster2 includes all publicly available single-nucleotide polymorphisms (SNPs) and indels from the 1000 Genomes Project2 (hereafter referred to as 1000G) as well as known disease variants from ClinVar3 and HGMD Public4. Alterations found more than four times in the homozygous state in 1000G or in HapMap5 are automatically regarded as neutral. Variants marked as pathogenic in ClinVar are automatically predicted to be disease causing, and the disease phenotype is displayed. We have integrated tests for regulatory features, including data from the ENCODE project6 and JASPAR7, and score the evolutionary conservation around DNA variants (Supplementary Methods). To reduce the number of false positive splice-site four barcodes left out). We first immobilized cells on glass surfaces (Supplementary Methods). The DNA probes were hybridized, imaged and then removed by DNase I treatment (88.5% ± 11.0% efficiency (± standard deviation); Supplementary Fig. 2 and Supplementary Note). The remaining signal was photobleached (Supplementary Fig. 3). Even after six hybridizations, mRNAs were observed at 70.9% ± 21.8% of the original intensity (Supplementary Fig. 4). We observed that 77.9% ± 5.6% of the spots that colocalized in the first two hybridizations also colocalized with the third hybridization (Fig. 1b and Supplementary Figs. 5 and 6). We quantified the mRNA abundances by counting the occurrence of corresponding barcodes in the cell (n = 37 cells; Supplementary Figs. 7 and 8). We also show that mRNAs can be stripped and rehybridized efficiently in adherent mammalian cells (Supplementary Figs. 9 and 10). Sequential barcoding has many advantages. First, it scales up quickly; with even two dyes the coding capacity is in principle unlimited. Second, during each hybridization, all available FISH probes against a transcript can be used, thereby increasing the brightness of the FISH signal. Last, barcode readout is robust, enabling full z stacks on native samples. This barcoding scheme is conceptually akin to sequencing transcripts in single cells with FISH. In contrast with the technique used by Ke et al.2, our method takes advantage of the high hybridization efficiency of FISH (>95% of the mRNAs are detected1,3) and the fact that base-pair resolution is usually not needed to uniquely identify a transcript. We note that FISH probes can also be designed to resolve a large number of splice isoforms and single-nucleotide polymorphisms3, as well as chromosome loci4, in single cells. In combination with our previous report of super-resolution FISH1, the sequential barcoding method will enable the transcriptome to be directly imaged at single-cell resolution in complex samples such as brain tissue.

Mutations in the gene encoding immunoglobulin μ-binding protein 2 cause spinal muscular atrophy with respiratory distress type 1

Classic spinal muscular atrophy (SMA) is caused by mutations in the telomeric copy of SMN1. Its product is involved in various cellular processes, including cytoplasmic assembly of spliceosomal small nuclear ribonucleoproteins, pre-mRNA processing and activation of transcription. Spinal muscular atrophy with respiratory distress (SMARD) is clinically and genetically distinct from SMA. Here we demonstrate that SMARD type 1 (SMARD1) results from mutations in the gene encoding immunoglobulin μ-binding protein 2 (IGHMBP2; on chromosome 11q13.2–q13.4). In six SMARD1 families, we detected three recessive missense mutations (exons 5, 11 and 12), two nonsense mutations (exons 2 and 5), one frameshift deletion (exon 5) and one splice donor-site mutation (intron 13). Mutations in mouse Ighmbp2 (ref. 14) have been shown to be responsible for spinal muscular atrophy in the neuromuscular degeneration (nmd) mouse, whose phenotype resembles the SMARD1 phenotype. Like the SMN1 product, IGHMBP2 colocalizes with the RNA-processing machinery in both the cytoplasm and the nucleus. Our results show that IGHMBP2 is the second gene found to be defective in spinal muscular atrophy, and indicate that IGHMBP2 and SMN share common functions important for motor neuron maintenance and integrity in mammals.

Leigh syndrome with nephropathy and CoQ10 deficiency due to decaprenyl diphosphate synthase subunit 2 (PDSS2) mutations.

Coenzyme Q(10) (CoQ(10)) is a vital lipophilic molecule that transfers electrons from mitochondrial respiratory chain complexes I and II to complex III. Deficiency of CoQ(10) has been associated with diverse clinical phenotypes, but, in most patients, the molecular cause is unknown. The first defect in a CoQ(10) biosynthetic gene, COQ2, was identified in a child with encephalomyopathy and nephrotic syndrome and in a younger sibling with only nephropathy. Here, we describe an infant with severe Leigh syndrome, nephrotic syndrome, and CoQ(10) deficiency in muscle and fibroblasts and compound heterozygous mutations in the PDSS2 gene, which encodes a subunit of decaprenyl diphosphate synthase, the first enzyme of the CoQ(10) biosynthetic pathway. Biochemical assays with radiolabeled substrates indicated a severe defect in decaprenyl diphosphate synthase in the patients fibroblasts. This is the first description of pathogenic mutations in PDSS2 and confirms the molecular and clinical heterogeneity of primary CoQ(10) deficiency.

Lack of myostatin results in excessive muscle growth but impaired force generation

The lack of myostatin promotes growth of skeletal muscle, and blockade of its activity has been proposed as a treatment for various muscle-wasting disorders. Here, we have examined two independent mouse lines that harbor mutations in the myostatin gene, constitutive null (Mstn−/−) and compact (Berlin High Line, BEHc/c). We report that, despite a larger muscle mass relative to age-matched wild types, there was no increase in maximum tetanic force generation, but that when expressed as a function of muscle size (specific force), muscles of myostatin-deficient mice were weaker than wild-type muscles. In addition, Mstn−/− muscle contracted and relaxed faster during a single twitch and had a marked increase in the number of type IIb fibers relative to wild-type controls. This change was also accompanied by a significant increase in type IIB fibers containing tubular aggregates. Moreover, the ratio of mitochondrial DNA to nuclear DNA and mitochondria number were decreased in myostatin-deficient muscle, suggesting a mitochondrial depletion. Overall, our results suggest that lack of myostatin compromises force production in association with loss of oxidative characteristics of skeletal muscle.

HomozygosityMapper—an interactive approach to homozygosity mapping

Homozygosity mapping is a common method for mapping recessive traits in consanguineous families. In most studies, applications for multipoint linkage analyses are applied to determine the genomic region linked to the disease. Unfortunately, these are neither suited for very large families nor for the inclusion of tens of thousands of SNPs. Even if less than 10 000 markers are employed, such an analysis may easily last hours if not days. Here we present a web-based approach to homozygosity mapping. Our application stores marker data in a database into which users can directly upload their own SNP genotype files. Within a few minutes, the database analyses the data, detects homozygous stretches and provides an intuitive graphical interface to the results. The homozygosity in affected individuals is visualized genome-wide with the ability to zoom into single chromosomes and user-defined chromosomal regions. The software also displays the underlying genotypes in all samples. It is integrated with our candidate gene search engine, GeneDistiller, so that users can interactively determine the most promising gene. They can at any point restrict access to their data or make it public, allowing HomozygosityMapper to be used as a data repository for homozygosity-mapping studies. HomozygosityMapper is available at http://www.homozygositymapper.org/.

The First Nuclear-Encoded Complex I Mutation in a Patient with Leigh Syndrome

Nicotinamide adenine dinucleotide (NADH):ubiquinone oxidoreductase (complex I) is the largest multiprotein enzyme complex of the respiratory chain. The nuclear-encoded NDUFS8 (TYKY) subunit of complex I is highly conserved among eukaryotes and prokaryotes and contains two 4Fe4S ferredoxin consensus patterns, which have long been thought to provide the binding site for the iron-sulfur cluster N-2. The NDUFS8 cDNA contains an open reading frame of 633 bp, coding for 210 amino acids. Cycle sequencing of amplified NDUFS8 cDNA of 20 patients with isolated enzymatic complex I deficiency revealed two compound heterozygous transitions in a patient with neuropathologically proven Leigh syndrome. The first mutation was a C236T (P79L), and the second mutation was a G305A (R102H). Both mutations were absent in 70 control alleles and cosegregated within the family. A progressive clinical phenotype proceeding to death in the first months of life was expressed in the patient. In the 19 other patients with enzymatic complex I deficiency, no mutations were found in the NDUFS8 cDNA. This article describes the first molecular genetic link between a nuclear-encoded subunit of complex I and Leigh syndrome.

Mutations in the Gene Encoding Gap Junction Protein α12 (Connexin 46.6) Cause Pelizaeus-Merzbacher–Like Disease

The hypomyelinating leukodystrophies X-linked Pelizaeus-Merzbacher disease (PMD) and Pelizaeus-Merzbacher-like disease (PMLD) are characterized by nystagmus, progressive spasticity, and ataxia. In a consanguineous family with PMLD, we performed a genomewide linkage scan using the GeneChip Mapping EA 10K Array (Affymetrix) and detected a single gene locus on chromosome 1q41-q42. This region harbors the GJA12 gene, which encodes gap junction protein alpha 12 (or connexin 46.6). Gap junction proteins assemble into intercellular channels through which signaling ions and small molecules are exchanged. GJA12 is highly expressed in oligodendrocytes, and, therefore, it serves as an excellent candidate for hypomyelination in PMLD. In three of six families with PMLD, we detected five different GJA12 mutations, including missense, nonsense, and frameshift mutations. We thereby confirm previous assumptions that PMLD is genetically heterogeneous. Although the murine Gja12 ortholog is not expressed in sciatic nerve, we did detect GJA12 transcripts in human sciatic and sural nerve tissue by reverse-transcriptase polymerase chain reaction. These results are in accordance with the electrophysiological finding of reduced motor and sensory nerve conduction velocities in patients with PMLD, which argues for a demyelinating neuropathy. In this study, we demonstrate that GJA12 plays a key role in central myelination and is involved in peripheral myelination in humans.

Mutations in PYCR1 cause cutis laxa with progeroid features.

Autosomal recessive cutis laxa (ARCL) describes a group of syndromal disorders that are often associated with a progeroid appearance, lax and wrinkled skin, osteopenia and mental retardation. Homozygosity mapping in several kindreds with ARCL identified a candidate region on chromosome 17q25. By high-throughput sequencing of the entire candidate region, we detected disease-causing mutations in the gene PYCR1. We found that the gene product, an enzyme involved in proline metabolism, localizes to mitochondria. Altered mitochondrial morphology, membrane potential and increased apoptosis rate upon oxidative stress were evident in fibroblasts from affected individuals. Knockdown of the orthologous genes in Xenopus and zebrafish led to epidermal hypoplasia and blistering that was accompanied by a massive increase of apoptosis. Our findings link mutations in PYCR1 to altered mitochondrial function and progeroid changes in connective tissues.