Mutation detection in the duplicated region of the polycystic kidney disease 1 (PKD1) gene in PKD1-linked Australian families

Screening for disease-causing mutations in the duplicated region of the PKD1 gene was performed in 17 unrelated Australian individuals with PKD1-linked autosomal dominant polycystic kidney disease. Exons 2-21 and 23-34 were assayed using PKD1-specific PCR amplification and direct sequencing. We have identified 12 novel probably pathogenic DNA variants, including five truncating mutations (Q563X, c.5105delAT, c.5159delG, S2269X, c.9847delC), two in-frame deletions (c.7472del3, c.9292del39), and two splice-site mutations (IVS14+1G>C, IVS16+1G>T). Three of the mutations (G381C, Y2185D, G2785D) were predicted to lead to the replacement of conserved amino acid residues, with ensuing changes in protein conformation. Defects in the duplicated region of PKD1 thus account for 63% of our patients. Together with the previously detected mutations (Q4041X, R4227P) in the 3 region of the gene, the study has achieved an overall mutation detection rate of 74%. In addition, we have detected 31 variants (nine novel and 22 previously published) that did not segregate with the disease and were considered to be neutral polymorphisms. Three of the nine novel polymorphisms were missense mutations with a predicted effect on protein conformation, emphasizing the problems of interpretation in PKD1 mutation screening.     

Gene conversion is a likely cause of mutation in PKD1

Approximately 70% of the gene responsible for the most common form of autosomal dominant polycystic kidney disease ( PKD1 ) is replicated in several highly homologous copies located more proximally on chromosome 16. We recently have described a novel technique for mutation detection in the duplicated region of PKD1 that circumvents the difficulties posed by these homologs. We have used this method to identify two patients with a nearly identical cluster of base pair substitutions in exon 23. Since pseudogenes are known to be reservoirs for mutation via gene conversion events for a number of other diseases, we decided to test whether these sequence differences in PKD1 could have arisen as a result of this mechanism. Using changes in restriction digest patterns, we were able to show that these sequence substitutions are also present in N23HA, a rodent-human somatic cell hybrid that contains only the PKD1 homologs. Moreover, these changes were also detected in total DNA from several affected and unaffected individuals that did not harbor this mutation in their PKD1 gene copy. This is the first example of gene conversion in PKD1 , and our findings highlight the importance of using gene-specific reagents in defining PKD1 mutations.      

Novel mutations in the duplicated region of PKD1 gene

Autosomal dominant polycystic kidney disease (ADPKD) exhibits a genetically heterogeneous transmission involving at least three different genes. PKD1 gene linked mutations are responsible for the disease in about 85% of ADPKD cases. The search for mutations is a very important step in understanding the molecular mechanisms underlying ADPKD. We undertook this study using denaturing gradient gel electrophoresis (DGGE), after a stage of long range PCR, to scan for mutations in the duplicated region of the PKD1 gene in French ADPKD families. This allowed us to identify eight novel mutations and several polymorphisms: among the mutations, three are nonsense mutations, two are deletions in the coding sequence leading to frameshift mutations, one is a splice mutation and two are highly probable missense mutations. In this paper, we also provide a review of the mutations reported so far which are widespread throughout the gene. Although no clear hot spot for mutation is apparent, we will focus on some clustering observed.     

Correlation of the feline PKD1 genetic mutation with cases of PKD diagnosed by pathological examination

Autosomal-dominant polycystic kidney disease (AD-PKD) is the most prevalent inherited genetic disease of cats, particularly affecting Persians. Using archived tissue samples from 44 cats a genotype was successfully obtained by real-time PCR for 43 cats. Twenty-five cats (18 Persians, 4 domestic longhair cats and 3 domestic shorthair (DSH) cats) were found to carry the AD-PKD mutation and all of these cats had macroscopic and/or microscopic evidence of renal cysts consistent with PKD. Eighteen cats were found to be wild-type. Twelve of these (all Persians) had no pathological evidence of PKD, but the remaining 6 cats had evidence of renal cystic lesions. On pathological review the cystic lesions in 4 (2 Persians and 2 DSH) of these 6 cats were considered not to be consistent with a primary diagnosis of PKD. Histological evidence of polycystic kidneys was, however, confirmed in the remaining 2 cats (1 DSH and 1 Bengal) and may indicate that other PKD-causing mutations exist in the feline population.     

Screening of the PKD1 duplicated region reveals multiple single nucleotide polymorphisms and a de novo mutation in Hellenic polycystic kidney disease families

Mutations in the PKD1 gene account for approximately 85% of cases with autosomal dominant polycystic kidney disease (ADPKD1; MIM# 601313), which is considered one of the most frequent monogenic disorders, with a frequency of approximately 1:1000. The main symptom is the formation of fluid-filled cysts in the kidneys and less often in other organs, such as the liver and pancreas. Since the cloning of the gene many mutations have been identified, although the screening is hampered by several unique features of this gene, the most significant one being that approximately 70% of the sequence at the 5'-end, is reiterated elsewhere on chromosome 16 with homology approaching 95%. Here, we used an oligonucleotide primer anchored in the unique part in exon 34, paired with a forward primer in exon 23 for specifically amplifying PKD1 sequences. We screened for mutations in samples from 32 Hellenic ADPKD families. We detected seven sequence variants, five of which most probably are single nucleotide polymorphisms (SNPs), especially useful for linkage analysis and disease association studies. One is a missense change, segregating with ADPKD in one family. The last one is a missense non-conservative change, H2921P, which appeared de novo in the proband, concurrently with the disease phenotype, and was passed on to another two generations. Two siblings who inherited the same haplotype as the proband, but not the de novo mutation, were not affected. This is only the fourth case of a molecularly documented de novo mutation in ADPKD. Somatic mosaicism in peripheral blood leukocytes of the proband was tested and excluded. Hum Mutat 16:176, 2000.     

Hereditary spastic paraplegia is a novel phenotype for germline de novo ATP1A1 mutation

Dominant mutations in ATP1A1, encoding the alpha-1 isoform of the Na⁺/K⁺-ATPase, have been recently reported to cause an axonal to intermediate type of Charcot-Marie-Tooth disease (ie, CMT2DD) and a syndrome with hypomagnesemia, intractable seizures and severe intellectual disability. Here, we describe the first case of hereditary spastic paraplegia (HSP) caused by a novel de novo (p.L337P) variant in ATP1A1. We provide evidence for the causative role of this variant with functional and homology modeling studies. This finding expands the phenotypic spectrum of the ATP1A1-related disorders, adds a piece to the larger genetic puzzle of HSP, and increases knowledge on the molecular mechanisms underlying inherited axonopathies (ie, CMT and HSP).     

应用变性高效液相色谱技术检测汉族人Ⅰ型多囊肾致病基因突变

目的通过采用变性高效液相色谱（denaturing high-pedormanee liquid chromatogtraphy，DHPLC）技术检测汉族人常染色体显性多囊肾病（autosomal dominant polycystic kidney disease，ADPKD）Ⅰ型致病基因PKD1的突变，建立更为快速、敏感的突变筛查系统。方法以来源于19个ADPKD家系的67名成员血样标本的基因组DNA为模板，通过长链PCR和巢式PCR联合扩增的方法扩增PKD1全编码区，然后采用DHPLC方法进行初步筛查，将存在异常色谱图的扩增产物经核苷酸测序，确定突变的具体位点和类型，并与以往采用单链构象多态性（single strand conformation polymorphism，SSCP）方法检测出的突变结果相比较。结果共检测出14个致病突变，包括10个错义突变、1个插入突变、1个缺失突变、2个无义突变，其中12个突变位点与之前SSCP的检测结果相同，另新发现nt32819G→A和nt37137T→C两个突变位点，突变检出率为73．7％。结论DHPLC方法可以作为更为有效筛查汉族人ADPKD PKD1突变位点的检测途径。     

Modification of the structure of peptidoglycan is a strategy to avoid detection by nucleotide-binding oligomerization domain protein 1

Nucleotide-binding oligomerization domain (NOD) protein 1 (NOD1) and NOD2 are pathogen recognition receptors that sense breakdown products of peptidoglycan (PGN) (muropeptides). It is shown that a number of these muropeptides can induce tumor necrosis factor alpha (TNF-alpha) gene expression without significant TNF-alpha translation. This translation block is lifted when the muropeptides are coincubated with lipopolysaccharide (LPS), thereby accounting for an apparently synergistic effect of the muropeptides with LPS on TNF-alpha protein production. The compounds that induced synergistic effects were also able to activate NF-kappaB in a NOD1- or NOD2-dependent manner, implicating these proteins in synergistic TNF-alpha secretion. It was found that a diaminopimelic acid (DAP)-containing muramyl tetrapeptide could activate NF-kappaB in a NOD1-dependent manner, demonstrating that an exposed DAP is not essential for NOD1 sensing. The activity was lost when the alpha-carboxylic acid of iso-glutamic acid was modified as an amide. However, agonists of NOD2, such as muramyl dipeptide and lysine-containing muramyl tripeptides, were not affected by amidation of the alpha-carboxylic acid of iso-glutamic acid. Many pathogens modify the alpha-carboxylic acid of iso-glutamic acid of PGN, and thus it appears this is a strategy to avoid recognition by the host innate immune system. This type of immune evasion is in particular relevant for NOD1.     

Deleterious mutation in FDX1L gene is associated with a novel mitochondrial muscle myopathy

Isolated metabolic myopathies encompass a heterogeneous group of disorders, with mitochondrial myopathies being a subgroup, with depleted skeletal muscle energy production manifesting either by recurrent episodes of myoglobinuria or progressive muscle weakness. In this study, we investigated the genetic cause of a patient from a consanguineous family who presented with adolescent onset autosomal recessive mitochondrial myopathy. Analysis of enzyme activities of the five respiratory chain complexes in our patients'' skeletal muscle showed severely impaired activities of iron sulfur (Fe-S)-dependent complexes I, II and III and mitochondrial aconitase. We employed exome sequencing combined with homozygosity mapping to identify a homozygous mutation, c.1A>T, in the FDX1L gene, which encodes the mitochondrial ferredoxin 2 (Fdx2) protein. The mutation disrupts the ATG initiation translation site resulting in severe reduction of Fdx2 content in the patient muscle and fibroblasts mitochondria. Fdx2 is the second component of the Fe-S cluster biogenesis machinery, the first being IscU that is associated with isolated mitochondrial myopathy. We suggest adding genetic analysis of FDX1L in cases of mitochondrial myopathy especially when associated with reduced activity of the respiratory chain complexes I, II and III.     

An unusual hormone pattern in a virilized woman affected by Sertoli-Leydig cell tumor. Report of a case

A 24-year-old woman was admitted to hospital because of hirsutism, virilism and amenorrhea, which had appeared 6 months earlier. Endocrinological evaluation showed a slightly elevated serum level of testosterone (1.2 +/- 0.05 ng/ml), normal plasma levels of dehydroepiandrosteronesulfate (DHEA-S) (2,070 +/- 6 ng/ml), androstenedione (1.8 +/- 0.5 ng/ml) and sex hormone-binding globulin (SHBG)(42 +/- 3 nM/L); there was normal urinary 17-ketosteroid (17-KS) excretion (11.7 mg/24 h), low urinary estrogen (E) excretion (3 +/- 0.4 micrograms/24 h), suppressed basal gonadotropin concentrations (LH 0.9 microUI/ml; FSH 3.2 microUI/ml) and an exaggerated response to the LH-RH test. At laparotomy, a monolateral ovarian tumor was found, which was proved histologically to be a Sertoli-Leydig cell tumor. After tumor ablation, a regular menstrual cycle followed and progressive reduction of virilism was noted. This was followed within 4 months by complete normalization of LH, FSH, estrogen and progesterone serum levels. The responsiveness to LH-RH also became normalized. Two years after this operation, the patient had a normal pregnancy. This case of virilization in a woman affected by a benign Sertoli-Leydig cell tumor was primarily characterized by an unusual response of the hypothalamopituitary axis against an endocrinological background of notable alteration of the androgen/estrogen ratio, where the androgens were slightly increased and the estrogens greatly reduced.