Pelizaeus-Merzbacher disease: a point mutation in exon 6 of the proteolipid protein (PLP) gene

Pelizaeus-Merzbacher disease has been known since 1885. It is characterized by severe dysmyelination of the central nervous system. We describe a new mutation in exon 6 of the proteolipid protein gene in a 9-year-old boy with severe connatal Pelizaeus-Merzbacher disease.     

Sporadic cardiac and skeletal myopathy caused by a de novo desmin mutation

Desmin myopathy is a familial or sporadic disorder characterized by intracytoplasmic accumulation of desmin in the muscle cells. We and others have previously identified desmin gene mutations in patients with familial myopathy, but close to 45% of the patients do not report previous family history of the disease. The present study was conducted to determine the cause of desmin myopathy in a sporadic patient presenting with symmetrical muscle weakness and atrophy combined with atrioventricular conduction block requiring a permanent pacemaker. A novel heterozygous R406W mutation in the desmin gene was identified by sequencing cDNA and genomic DNA. Expression of a construct containing the patient's mutant desmin cDNA in SW13 (vim-) cells demonstrated a high pathogenic potential of the R406W mutation. This mutation was not found in the patient's father, mother or sister by sequencing and restriction analysis. Testing with five microsatellite markers and four intragenic single nucleotide polymorphisms excluded alternative paternity. Haplotype analysis indicates that the patient's father was germ-line mosaic for the desmin mutation. We conclude that de novo mutations in the desmin gene may be the cause of sporadic forms of desmin-related cardiac and skeletal myopathy.     

Family with Pelizaeus-Merzbacher disease/X-linked spastic paraplegia and a nonsense mutation in exon 6 of the proteolipid protein gene

We report on a C-to-T transition in exon 6 of the PLP gene in a male with Pelizaeus-Merzbacher disease/X-linked spastic paraplegia. The transition changes a glutamine at amino acid residue 233 to a termination codon. This premature stop codon probably results in a truncated protein that is not functional. Six other relatives were analyzed for the mutation and two female carriers were identified. Autopsy data on one male are presented. Am. J. Med. Genet. 71:357–360, 1997. © 1997 Wiley-Liss, Inc.     

Nonsense mutation in exon 3 of the proteolipid protein gene (PLP) in a family with an unusual form of Pelizaeus-Merzbacher disease

We report a G→A transition at nucleotide 431 of the proteolipid protein gene (PLP) results in a nonsense codon in a family with an unusual form of Pelizaeus-Merzbacher disease (PMD). The mutation, which creates a second AluI restriction site, results in a nonsense mutation in PLP. The clinical picture resembles somewhat that of X-linked spastic paraplegia (SPG). It differs from this and both the classical and connatal forms of PMD in that it is relatively mild in form, onset is delayed beyond age 2 years, nystagmus is absent, tremors are prominent, mental retardation is not severe, some patients show dementia or personality disorders, the disease is progressive rather than static in some, and several females show signs of disease. The nonsense mutation, which is in exon 3B, should block the synthesis of normal PLP but spare DM20, the isoform whose persistence has been associated with mild forms of PLP-associated disease in both humans and mice. Am. J. Med Genet. 69:121–125, 1997. © 1997 Wiley-Liss, Inc.     

Connatal Pelizaeus-Merzbacher disease: A missense mutation in exon 4 of the proteolipid protein (PLP) gene

We investigated the proteolipid protein (PLP) gene in two brothers in a Japanese family with a connatal form of Pelizaeus-Merzbacher disease (PMD). Direct sequencing of the PLP gene revealed an A-to-T transition in exon 4, which led to an Asp-to-Val substitution at re-sidue 202. Their mother was confirmed to be heterozygous for the mutation. The mutation was not found in 78 X-chromosomes of normal Japanese individuals. A correlation between the clinical severity of the disease in the brothers and the Asp202-to-Val mutation in the PLP gene was suggested. Received: April 24, 1998 / Accepted: May 29, 1998     

Improving the rigor of mutation reports: Biologic parentage and de novo mutations

The accurate determination and dissemination of the causality or pathogenicity of human DNA sequence variants is a crucial function of genetics journals. Published reports of pathogenic mutations are a common source of information for mutation databases, which are in turn used to make recommendations to patients. One of the strongest pieces of evidence in support of causality or pathogenicity for mutation reports is the occurrence of a de novo mutation. Yet, many publications describing such changes do not demonstrate that the mutation is truly de novo, by performing biologic parentage testing. I argue here that all mutation reports that describe such mutations should include biologic parentage testing, or in the absence of such testing, the mutation should be described as “apparently de novo.” This proposed standard should improve the transparency of the evidence that underlies our literature, and ultimately improve the databases of mutations in human disease. Hum Mutat 33:1501–1502, 2012. Published 2012 Wiley Periodicals, Inc.*     

Case report: de novo BRCA2 gene mutation in a 35-year-old woman with breast cancer

In this report, we describe a patient with a de novo BRCA2 gene mutation (5301insA) who developed early onset breast cancer with no strong family history of the disease. Only three similar instances have been reported previously. Subsequent site-specific analysis in her parents showed that neither carried the mutation previously identified in their daughter. Various possible explanations for this finding were excluded. Paternity was confirmed using 13 highly polymorphic markers, thereby illustrating that the patient carried a de novo mutation in the BRCA2 gene. The 5301insA mutation has been well described and reported many times in the Breast Cancer Information Core online Breast Cancer Mutation database. This finding illustrates the importance of determining the incidence of de novo BRCA mutations and is of significant clinical value to breast cancer prevention and management. Our case report presents the fourth case in which a de novo germline mutation in a BRCA1/2 gene has been identified.     

Ile225Thr loop mutation in the lipoprotein lipase (LPL) gene is a de novo event

Mutations in the lipoprotein lipase (LPL) gene are the most important cause of familial chylomicronemia with over 70 mutations being recorded to date. Thus far de novo mutations have not been described. Here we report on the molecular analysis of the family of a patient previously reported to be LPL deficient on the basis of compound heterozygosity for the Arg²⁴³His and Ile²²⁵Thr mutations, the latter being the first and only mutation identified in the loop region of LPL. Both parents of the propositus were screened for the presence of these two mutations to confirm their status as obligate heterozygotes and to determine the mutation allocation. Although paternal inheritance of the Arg²⁴³His allele could be established, maternal DNA did not show carrier status for the Ile²²⁵Thr substitution. An examination of maternity, using LPL restriction fragment length polymorphisms four polymorphic CA repeats and ApoE genotypes, was consistent with correct biological parentage for the propositus. Therefore, we conclude that the Ile²²⁵Thr mutation constitutes a de novo event, the first to be reported in the LPL gene. Am. J. Med. Genet. 78:313–316, 1998. © 1998 Wiley-Liss, Inc.     

De novo mutation in CACNA1A caused acetazolamide-responsive episodic ataxia

With the recent report of mutations in the calcium channel gene CACNA1A in two families with episodic ataxia type 2, we investigated a patient with nonfamilial episodic vertigo and ataxia responsive to acetazolamide for similar mutations. Single-strand conformation polymorphism (SSCP) analysis of exon 23 identified an extra band in the patient that was not present in other relatives or in normal controls. Exon 23 of the patient showed a spontaneous C to T substitution at position 4410 resulting in an early stop codon. Patients with nonfamilial episodic ataxia may respond to acetazolamide and may have mutations in CACNA1A. Am. J. Med. Genet. 77:298–301, 1998. © 1998 Wiley-Liss, Inc.     

A de novo mutation in PRICKLE1 in fetal agenesis of the corpus callosum and polymicrogyria

Abstract

Homozygous recessive mutations in the PRICKLE1 gene were originally reported in three consanguineous families with myoclonic epilepsy. Subsequently, several studies have identified neurological abnormalities in animal models with both heterozygous and homozygous mutations in PRICKLE1 orthologues, including epilepsy in flies and in mice with heterozygous PRICKLE1 mutations. We describe a fetus with a novel de novo mutation in PRICKLE1 associated with agenesis of the corpus callosum.     

一例由 KCNJ6基因新发变异导致的Keppen-Lubinsky综合征患儿的临床及遗传学分析

目的:探讨1例由 KCNJ6基因新发变异导致的Keppen-Lubinsky综合征患儿的临床及遗传学特点。 方法:应用全外显子组测序对患儿及其父母进行基因检测,并用生物信息学软件预测其危害性,并通过蛋白质结构模拟分析其影响。结果:患儿具有特殊面容,表现为大眼、鼻翼发育不全、小后缩下颌及早衰模样,同...     

Double de novo mutations of ELA2 in cyclic and severe congenital neutropenia

Heterozygous mutations of ELA2, encoding the protease neutrophil elastase (NE), cause either autosomal dominant cyclic neutropenia or severe congenital neutropenia (SCN). Three hypotheses have been proposed for how allelic mutations produce these different disorders: 1) disruption of proteolytic activity; 2) mislocalization of the protein; or 3) destabilization of the protein resulting in induction of the unfolded protein response. As with other dominant diseases with reduced reproductive fitness, sporadic cases can result from new mutations not inherited from either parent. Here we report an exceptional genetic phenomenon in which both a cyclic neutropenia patient and an SCN patient each possess two new ELA2 mutations. Because of the rarity of the phenomenon, we investigated the origins of the mutations and found that both arise nonmosaically and in cis from the paternally-inherited allele. Moreover, these cases offer a unique opportunity to investigate molecular pathways distinguishing these two forms of hereditary neutropenia. We have characterized the mutants separately and in combination, with respect to their effects on proteolysis, subcellular trafficking, and induction of the unfolded protein response. Each pair of mutations acts more or less additively to produce equivalent net effects on reducing proteolytic activity and induction of the unfolded protein response, yet each has different and somewhat opposing effects on disturbing subcellular localization, thus offering support for a role for protein mistrafficking as a disease mechanism.     

A de novo mutation in PRICKLE1 associated with myoclonic epilepsy and autism spectrum disorder

Homozygous recessive mutations in the PRICKLE1 gene were first described in three consanguineous families with myoclonic epilepsy. Subsequent studies have identified neurological abnormalities in humans and animal models with both heterozygous and homozygous mutations in PRICKLE1 orthologs. We describe a 7-year-old with a novel de novo missense mutation in PRICKLE1 associated with epilepsy, autism spectrum disorder and global developmental delay.     

A de novo missense mutation of the FUS gene in a “true” sporadic ALS case

Mutations in the Cu/Zn superoxide dismutase (SOD1), transactive response (TAR)-DNA binding protein (TARDBP) and fused in sarcoma (FUS) genes account for approximately 1 third of familial amyotrophic lateral sclerosis (ALS) cases. Mutations in these genes have been found in 1% to 2% of apparently sporadic cases. We present the first case of an ALS patient carrying a de novo missense mutation of the FUS gene (c.1561C>T, p.R521C). This report highlights the importance of screening ALS patients, both familial and sporadic, for FUS mutations and also suggests that de novo mutations is a relevant mechanism underlying sporadic neurodegenerative disease.     

A de novo missense mutation (R1623Q) of the SCN5A gene in a Japanese girl with sporadic long QT syndrome

Two missense mutations and a nine-nucleotide deletion of the cardiac sodium channel (SCN5A) gene have been shown to cause long QT syndrome (LQTS) in several familial cases. We identified a novel missense mutation (R1623Q) of the SCN5A gene in a Japanese girl with sporadic LQTS. We used polymerase chain reaction, single-strand conformation polymorphism analysis and DNA sequence analysis to identify a mutation of the SCN5A gene in the patient. A single nucleotide substitution of guanine to adenine, in codon 1623, changed the coding sense of the SCN5A from arginine to glutamine (R1623Q) in the S4 segment of domain IV which is a highly conserved region of the SCN5A. This mutation was not identified in the unaffected biological parents and brother of the patient, and 100 normal, unrelated individuals. This finding is the first evidence of a de novo mutation in SCN5A associated with LQTS. Hum Mutat 11:481, 1998. © 1998 Wiley-Liss, Inc.     

A de novo nonsense mutation of the FUS gene in an apparently familial amyotrophic lateral sclerosis case

Mutations in C9ORF72, SOD1, TARDBP, and FUS genes account for approximately two-third of familial cases and 5% of sporadic amyotrophic lateral sclerosis (ALS) cases. We present the first case of an ALS patient carrying a de novo nonsense mutation in exon 14 of the FUS gene (c.1483c>t; p.R495X) with an apparently familial ALS. This mutation causes a phenotype characterized by a young age at onset, a rapid course (<24 months), and a bulbar onset with early respiratory involvement with a predominant lower motor neuron disease. De novo mutations could account for a sizable number of apparently sporadic ALS patients carrying mutations of ALS-related genes.     

Pelizaeus-Merzbacher病的分子遗传学研究进展

Pelizaeus-Merzbacher病(PMD)是罕见的遗传性脑白质营养不良病,是由于蛋白脂蛋白(poteolipid protein 1,PLP1)基因的突变导致髓鞘不能正常形成所致,其中以PLP1基因的重复突变最多见.PLP1基因不同的突变可导致特定的疾病类型,且基因型和表型之间总体上存在对应关系.本文对PMD的分子遗传学特点及近期对该病分子、细胞机制的认识进行综述.     

Aberrant trafficking of a proteolipid protein in a mild Pelizaeus-Merzbacher disease

Pelizaeus-Merzbacher disease (PMD) is a rare X-linked leukodystrophy caused by proteolipid protein 1 (PLP1) gene mutations. Previous studies indicated that proteolipid proteins (PLPs) with disease-associated mutations are misfolded and trapped in the endoplasmic reticulum (ER) during transportation to the cell surface, which eventually leads to oligodendrocyte cell death in PMD. Here we report a PMD patient with a very mild phenotype carrying a novel mutation (485G-->T) in exon 4 of the PLP1 gene that causes a Trp(162)Leu substitution in the protein. We also investigated intracellular trafficking of this mutant PLP in COS-7 cells. Transiently transfected mutant PLP(W162L) fused to an enhanced green fluorescent protein (EGFP) or a short peptide tag was not carried to the plasma membrane. However, in contrast to previous studies, this mutant PLP was not retained in the ER, indicating an escape of the newly translated protein from the quality control machinery. We also found that the mutant PLP accumulated in the nuclear envelope (NE) in a time-dependent manner. This mutant PLP, with its distribution outside the ER and a very mild phenotype, supports the idea that accumulation of misfolded mutant protein in the ER causes the severe phenotype of PMD.