X-linked infantile spinal muscular atrophy (XL-SMA) is an X-linked disorder presenting with the clinical features hypotonia, areflexia, and multiple congenital contractures (arthrogryposis) associated with loss of anterior horn cells and infantile death. To identify the XL-SMA disease gene, we performed large-scale mutation analysis in genes located between markers DXS8080 and DXS7132 (Xp11.3-Xq11.1). This resulted in detection of three rare novel variants in exon 15 of UBE1 that segregate with disease: two missense mutations (c.1617 G-->T, p.Met539Ile; c.1639 A-->G, p.Ser547Gly) present each in one XL-SMA family, and one synonymous C-->T substitution (c.1731 C-->T, p.Asn577Asn) identified in another three unrelated families. Absence of the missense mutations was demonstrated for 3550 and absence of the synonymous mutation was shown in 7914 control X chromosomes; therefore, these results yielded statistical significant evidence for the association of the synonymous substitution and the two missense mutations with XL-SMA (p = 2.416 x 10(-10), p = 0.001815). We also demonstrated that the synonymous C-->T substitution leads to significant reduction of UBE1 expression and alters the methylation pattern of exon 15, implying a plausible role of this DNA element in developmental UBE1 expression in humans. Our observations indicate first that XL-SMA is part of a growing list of neurodegenerative disorders associated with defects in the ubiquitin-proteasome pathway and second that synonymous C-->T transitions might have the potential to affect gene expression.

In mammals, the Major Histocompatibility Complex class I and II gene clusters are separated by an ∼700-kb stretch of sequence called the MHC class III region, which has been associated with susceptibility to numerous diseases. To facilitate understanding of this medically important and architecturally interesting portion of the genome, we have sequenced and analyzed both the human and mouse class III regions. The cross-species comparison has facilitated the identification of 60 genes in human and 61 in mouse, including a potential RNA gene for which the introns are more conserved across species than the exons. Delineation of global organization, gene structure, alternative splice forms, protein similarities, and potential cis-regulatory elements leads to several conclusions: (1) The human MHC class III region is the most gene-dense region of the human genome: >14% of the sequence is coding, ∼72% of the region is transcribed, and there is an average of 8.5 genes per 100 kb. (2) Gene sizes, number of exons, and intergenic distances are for the most part similar in both species, implying that interspersed repeats have had little impact in disrupting the tight organization of this densely packed set of genes. (3) The region contains a heterogeneous mixture of genes, only a few of which have a clearly defined and proven function. Although many of the genes are of ancient origin, some appear to exist only in mammals and fish, implying they might be specific to vertebrates. (4) Conserved noncoding sequences are found primarily in or near the 5'-UTR or the first intron of genes, and seldom in the intergenic regions. Many of these conserved blocks are likely to be cis-regulatory elements.

Background-The importance of germ-line mosaicism in genetic disease is probably underestimated, even though recent studies indicate that it may be involved in 10% to 20% of apparently de novo cases of several dominantly inherited genetic diseases. Methods and Results-We describe here a case of repeated germ-line transmission of a severe form of long-QT syndrome (LQTS) from an asymptomatic mother with mosaicism for a mutation in the cardiac sodium channel, SCN5A. A male infant was diagnosed with ventricular arrhythmias and cardiac decompensation in utero at 28 weeks and with LQTS after birth, ultimately requiring cardiac transplantation for control of ventricular tachycardia. The mother had no ECG abnormalities, but her only previous pregnancy had ended in stillbirth with evidence of cardiac decompensation at 7 months' gestation. A third pregnancy also ended in stillbirth at 7 months, again with nonimmune fetal hydrops. The surviving infant was found to have a heterozygous mutation in SCN5A (R1623Q), previously reported as a de novo mutation causing neonatal ventricular arrhythmia and LQTS. Initial studies of the mother detected no genetic abnormality, but a sensitive restriction enzyme-based assay identified a small (8% to 10%) percentage of cells harboring the mutation in her blood, skin, and buccal mucosa. Cord blood from the third fetus also harbored the mutant allele, suggesting that all 3 cases of late-term fetal distress resulted from germ-line transfer of the LQTS-associated mutation. Conclusions-Recurrent late-term fetal loss or sudden infant death can result from unsuspected parental mosaicism for LQTS-associated mutations, with important implications for genetic counseling.

The chloroplast genome of most land plants is highly conserved. In contrast, physical and gene mapping studies have revealed a highly rearranged chloroplast genome in species representing four families of ferns. In all four, there has been a rare duplication of the psbA gene and the order of the psbA, 16S, and 23S rRNA genes has been inverted. Our analysis shows that the described rearrangement results from a minimum of two inversions within the inverted repeat. This chloroplast DNA structure provides unambiguous evidence that phylogenetically links families of ferns once thought to belong to different major evolutionary lineages.The chloroplast DNA (cpDNA) of most land plants is a circular molecule 120-160 kilobases (kb), which codes for 120 genes and typically contains an inverted repeat (IR). These repeated sequences range in size from 9.4 to 76 kb, code for several genes including those for 16S and 23S rRNA, and are separated by small single copy (SSC) and large single copy (LSC) regions (1-3). Gene order is remarkably similar in the cpDNAs of the fern Osmunda, the gymnosperm Ginkgo, and many angiosperms and differs from that in the bryophyte Marchantia primarily by a 30-kb inversion (4-6). This 30-kb inversion places the psbA gene close to the IR in Osmunda and in most gymnosperms and angiosperms (3, 4). The rRNA genes are part of an operon typically oriented with the 16S gene nearer to the LSC region and the 23S gene closer to the SSC region (Fig. 1A). Structural changes (such as gene duplications, gene losses, and inversions) are relatively rare and have been documented mainly in angiosperms (refs. 7-10, but see ref. 11).In this report, we describe the chloroplast genome shared by several ferns and show that it differs considerably from the typical structure detailed above. These differences provide molecular evidence about the evolutionary relationships of these ferns, which have been in dispute, and demonstrate that the chloroplast genomes of groups other than angiosperms have been markedly changed during evolution. Evidence concerning relationships at higher taxonomic levels is especially needed in ferns in which different phylogenies based on morphological characters are not concordant (12-15). Reasons for these discrepancies include (i) the use of narrative methods of phylogenetic analysis where the line of reasoning and the characters used are not made explicit, (ii) difficulties in identifying homologous parts in structurally simple organisms, and (iii) problems in determining the primitive or advanced states ofcharacters. The latter situation arises from the paucity of evidence from the fossil record (15-17) and the difficulty in choosing appropriate outgroups for many extant taxa due to the antiquity of ferns and the loss of many potential outgroups through extinction. MATERIALS AND METHODSLeaves of Polystichum acrostichoides (Michx.) Schott were collected in western Massachusetts and a voucher specimen (Sprague in 1986) was deposited at the Dean Herbarium of Indiana University. Leaves ...

No abstract

Neuromuscular diseases (NMD) account for a significant proportion of infant and childhood mortality and devastating chronic disease. Determining the specific diagnosis of NMD is challenging due to thousands of unique or rare genetic variants that result in overlapping phenotypes. We present four unique childhood myopathy cases characterized by relatively mild muscle weakness, slowly progressing course, mildly elevated creatine phosphokinase (CPK), and contractures. We also present two additional cases characterized by severe prenatal/neonatal myopathy. Prior extensive genetic testing and histology of these cases did not reveal the genetic etiology of disease. Here, we applied whole exome sequencing (WES) and bioinformatics to identify likely causal pathogenic variants in each pedigree. In two cases, we identified novel pathogenic variants in COL6A3. In a third case, we identified novel likely pathogenic variants in COL6A6 and COL6A3. We identified a novel splice variant in EMD in a fourth case. Finally, we classify two cases as calcium channelopathies with identification of novel pathogenic variants in RYR1 and CACNA1S. These are the first cases of myopathies reported to be caused by variants in COL6A6 and CACNA1S. Our results demonstrate the utility and genetic diagnostic value of WES in the broad class of NMD phenotypes.

Homo sapiens possess several trypsinogen or trypsinogen-like genes of which three (PRSS1, PRSS2, and PRSS3) produce functional trypsins in the digestive tract. PRSS1 and PRSS2 are located on chromosome 7q35, while PRSS3 is found on chromosome 9p13. Here, we report a variation of the theme of new gene creation by duplication: the PRSS3 gene was formed by segmental duplications originating from chromosomes 7q35 and 11q24. As a result, PRSS3 transcripts display two variants of exon 1. The PRSS3 transcript whose gene organization most resembles PRSS1 and PRSS2 encodes a functional protein originally named mesotrypsinogen. The other variant is a fusion transcript, called trypsinogen IV. We show that the first exon of trypsinogen IV is derived from the noncoding first exon of LOC120224, a chromosome 11 gene. LOC120224 codes for a widely conserved transmembrane protein of unknown function. Comparative analyses suggest that these interchromosomal duplications occurred after the divergence of Old World monkeys and hominids. PRSS3 transcripts consist of a mixed population of mRNAs, some expressed in the pancreas and encoding an apparently functional trypsinogen and others of unknown function expressed in brain and a variety of other tissues. Analysis of the selection pressures acting on the trypsinogen gene family shows that, while the apparently functional genes are under mild to strong purifying selection overall, a few residues appear under positive selection. These residues could be involved in interactions with inhibitors.

Purpose: X-linked infantile spinal-muscular atrophy (XL-SMA) is a rare disorder, which presents with the clinical characteristics of hypotonia, areflexia, and multiple congenital contractures (arthrogryposis) associated with loss of anterior horn cells and death in infancy. We have previously reported a single family with XL-SMA that mapped to Xp11.3-q11.2. Here we report further clinical description of XL-SMA plus an additional seven unrelated (XL-SMA) families from North America and Europe that show linkage data consistent with the same region. Methods: We first investigated linkage to the candidate disease gene region using microsatellite repeat markers. We further saturated the candidate disease gene region using polymorphic microsatellite repeat markers and single nucleo-