Identification of a novel lipase gene mutated in lpd mice with hypertriglyceridemia and associated with dyslipidemia in humans

Triglyceride (TG) metabolism is crucial for whole body and local energy homeostasis and accumulating evidence suggests an independent association between plasma TG concentration and increased atherosclerosis risk. We previously generated a mouse insertional mutation lpd (lipid defect) whose phenotype included elevated plasma TG and hepatic steatosis. Using shotgun sequencing (approximately 500 kb) and bioinformatics, we have now identified a novel lipase gene lpdl (lpd lipase) within the lpd locus, and demonstrate the genetic disruption of exon 10 of lpdl in the lpd mutant locus. lpdl is highly expressed in the testis and weakly expressed in the liver of 2-week old mice. Human LPDL cDNA was subsequently cloned, and was found to encode a 460AA protein with 71% protein sequence identity to mouse lpdl and approximately 35% identity to other known lipases. We next sequenced the human LPDL gene exons in hypertriglyceridemic subjects and normal controls, and identified seven SNPs within the gene exons and six SNPs in the adjacent introns. Two hypertriglyceridemic subjects were heterozygous for a rare DNA variant, namely 164G>A (C55Y), which was absent from 600 normal chromosomes. Two other coding SNPs were associated with variation in plasma HDL cholesterol in independent normolipidemic populations. Using bioinformatics, we identified another novel lipase designated LPDLR (for 'LPDL related lipase'), which had 44% protein sequence identity with LPDL. Together with the phospholipase gene PSPLA1, LPDL and LPDLR form a new lipase gene subfamily, which is characterized by shortened lid motif. Study of this lipase subfamily may identify novel molecular mechanisms for plasma and/or tissue TG metabolism.     

Characterization of a mutation commonly associated with persistent stuttering: evidence for a founder mutation

Stuttering is a disorder that affects the fluency of speech. It has been shown to have high heritability and has recently been linked to mutations in the GNPTAB gene. One such mutation, Glu1200Lys, has been repeatedly observed in unrelated families and individual cases. Eight unrelated individuals carrying this mutation were analyzed in an effort to distinguish whether these arise from repeated mutation at the same site, or whether they represent a founder mutation with a single origin. Results show that all 12 chromosomes carrying this mutation share a common haplotype in this region, indicating that it is a founder mutation. Further analysis estimated the age of this allele to be ～ 572 generations. Construction of a cladogram tracing the mutation through our study sample also supports the founder mutation hypothesis.     

Positional cloning of a novel gene on chromosome 16q causing Bardet-Biedl syndrome (BBS2)

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous autosomal recessive disorder with the primary clinical features of obesity, pigmented retinopathy, polydactyly, hypogenitalism, mental retardation and renal anomalies. Associated features of the disorder include diabetes mellitus, hypertension and congenital heart disease. There are six known BBS loci, mapping to chromosomes 2, 3, 11, 15, 16 and 20. The BBS2 locus was initially mapped to an 18 cM interval on chromosome 16q21 with a large inbred Bedouin kindred. Further analysis of the Bedouin population allowed for the fine mapping of this locus to a 2 cM region distal to marker D16S408. Physical mapping and sequence analysis of this region resulted in the identification of a number of known genes and expressed sequence tag clusters. Mutation screening of a novel gene (BBS2) with a wide pattern of tissue expression revealed homozygous mutations in two inbred pedigrees, including the large Bedouin kindred used to initially identify the BBS2 locus. In addition, mutations were found in three of 18 unrelated BBS probands from small nuclear families.     

Gene forα2(I) collagen is on mouse chromosome 6 not 16

Collagen is the most abundant protein in the animal world and a principal component, of the extracellular matrix of tissues. Type I collagen is composed of two ₁ chains and one 2 chain. The human 2(I) locus (COL1A2)has been assigned to human chromosome 7q21.3–q22.1. Here, we report the mapping of its murine counterpart Colla-2to mouse chromosome 6 (MMU6) by Southern blotting using somatic cell hybrids. This result disagrees with the previously reported mapping of Colla-2to MMU16 by immunochemical techniques. Our results are supported by comparative mapping data showing conserved homology between regions of human chromosome 7 and mouse chromosome 6.     

Evidence of dependence of lipoprotein(a) on triglyceride and high-density lipoprotein metabolism

Lipoprotein(a) [Lp(a)] is a complex lipoprotein consisting of a low-density lipoprotein (LDL)-like ApoB₁₀₀-containing core particle covalently bound to apo(a), a large functionally complex glycoprotein. The mechanisms of Lp(a) metabolism and its interactions with cell-surface lipoprotein receptors are incompletely understood. In this study, we investigated the relationship of Lp(a) to other lipoproteins at high and normal levels of serum triglycerides (TGs). We measured serum lipid and Lp(a) particle concentrations in 148 unselected primary- and secondary-prevention patients. Subjects with TG > 200 mg/dL were classified as having high TG in accordance with National Cholesterol Education Program Adult Treatment Panel III guidelines. Our analysis revealed mean TG levels of 100 and 270 mg/dL in the normal and high TG groups, respectively. Lp(a)-C, Lp(a)-P, and Lp(a) cholesterol content per particle [Lp(a)-C/Lp(a)-P] did not differ between groups. At normal TG levels, stepwise multiple linear regression revealed that Lp(a)-P correlated with Lp(a)-C (P < 10^?6), ApoAI (P = .0001), the high-density lipoprotein cholesterol subfraction ratio (HDL₂-C/HDL₃-C; P = .002), and dense very-low-density lipoprotein cholesterol (VLDL₃-C; P = .04), overall model R = 0.74. At high TG levels, Lp(a)-P very strongly correlated primarily with HDL₂-C/HDL₃-C and TG-related variables with minimal dependence on Lp(a)-C (P = .09), overall model R = 0.96. These findings provide evidence of shared metabolic mechanisms for Lp(a), HDL, TG, and very low-density lipoprotein at high serum TG. Future studies are needed to elucidate common mechanisms, enzymes, and receptors involved in Lp(a) and HDL/TG metabolism with a focus on how these mechanisms are modified in the setting of hypertriglyceridemia.     

OSBPL10, a novel candidate gene for high triglyceride trait in dyslipidemic Finnish subjects, regulates cellular lipid metabolism

Analysis of variants in three genes encoding oxysterol-binding protein (OSBP) homologues (OSBPL2, OSBPL9, OSBPL10) in Finnish families with familial low high-density lipoprotein (HDL) levels (N?=?426) or familial combined hyperlipidemia (N?=?684) revealed suggestive linkage of OSBPL10 single-nucleotide polymorphisms (SNPs) with extreme end high triglyceride (TG; >90th percentile) trait. Prompted by this initial finding, we carried out association analysis in a metabolic syndrome subcohort (Genmets) of Health2000 examination survey (N?=?2,138), revealing association of multiple OSBPL10 SNPs with high serum TG levels (>95th percentile). To investigate whether OSBPL10 could be the gene underlying the observed linkage and association, we carried out functional experiments in the human hepatoma cell line Huh7. Silencing of OSBPL10 increased the incorporation of [³H]acetate into cholesterol and both [³H]acetate and [³H]oleate into triglycerides and enhanced the accumulation of secreted apolipoprotein B100 in growth medium, suggesting that the encoded protein ORP10 suppresses hepatic lipogenesis and very-low-density lipoprotein production. ORP10 was shown to associate dynamically with microtubules, consistent with its involvement in intracellular transport or organelle positioning. The data introduces OSBPL10 as a gene whose variation may contribute to high triglyceride levels in dyslipidemic Finnish subjects and provides evidence for ORP10 as a regulator of cellular lipid metabolism.     

Meningocerebrovascular amyloidosis associated with a novel transthyretin mis-sense mutation at codon 18 (TTRD 18G)

We describe a novel transthyretin mutation at codon 18 where Asp is replaced by Gly (D18G) in a Hungarian kindred. This mutation is associated with meningocerebrovascular amyloidosis, producing dementia, ataxia, and spasticity. Fifty different transthyretin mutations are related to amyloid deposition, typically producing a peripheral neuropathy or cardiac dysfunction. These symptoms are absent in this family. Up to now, amyloid-beta (A beta), cystatin C, and prion proteins have been known to be deposited as amyloid in the brain, leading to stroke or dementia. With this report we establish that transthyretin amyloid deposition can also produce central nervous system dysfunction as the major clinical symptom.     

Characterization of a novel KRAS mutation identified in Noonan syndrome

Noonan syndrome (NS) is the most common non-chromosomal syndrome seen in children and is characterized by short stature, dysmorphic facial features, chest deformity, a wide range of congenital heart defects and developmental delay of variable degree. Mutations in the Ras/mitogen-activated protein kinase (MAPK) signaling pathways cause about 70% of NS cases with a KRAS mutation present in about 2%. In a cohort of 65 clinically confirmed NS patients of Japanese origin, we screened for mutations in the RAS genes by direct sequencing. We found a novel mutation in KRAS with an amino acid substitution of asparagine to serine at codon 116 (N116S). We analyzed the biological activity of this mutant by ectopic expression of wild-type or mutant KRAS. NS-associated KRAS mutation resulted in Erk activation and active Ras-GTP levels, and exhibited mild cell proliferation. In addition, kras-targeted morpholino knocked-down zebrafish embryos caused heart and craniofacial malformations, while the expression of mutated kras resulted in maldevelopment of the heart. Our findings implicate that N116S change in KRAS is a hyperactive mutation which is a causative agent of NS through maldevelopment of the heart.     

Carnitine/acylcarnitine translocase deficiency (neonatal phenotype): successful prenatal and postmortem diagnosis associated with a novel mutation in a single family

The neonatal phenotype of carnitine-acylcarnitine translocase (CACT) deficiency is one of the most severe and usually lethal mitochondrial fat oxidation disorders characterized by hypoketotic hypoglycemia, hyperammonemia, cardiac abnormalities, and early death. In this study, the proband was the daughter of consanguineous Hispanic parents. At 36 h of life, she had bradycardia and died at 4 days of age without a specific diagnosis. In a subsequent pregnancy, prenatal counseling and amniocentesis were provided. Incubation of the amniocytes from this pregnancy and fibroblasts (from the dead proband) with [16-(2)H(3)]palmitic acid and analysis by tandem mass spectrometry revealed an increasedconcentration of [16-(2)H(3)]palmitoylcarnitine, suggesting the diagnoses of either CACT or carnitine palmitoyltransferase II (CPT-II) deficiency. CACT enzyme activity was absent in both cell lines. Molecular investigation of cDNA from the dead proband and her affected sibling revealed aberrant CACT cDNA species, including exon 3 skipping, both exon 3 and 4 skipping, and a 13-bp insertion at cDNA position 388. Investigation of these cell lines for mutations affecting CACT RNA processing by analysis of CACT gene sequences, including intron and exon boundaries, revealed a single nucleotide G deletion at the donor site in intron 3 which resulted in exon skipping and a 13-bp insertion. The proband and her affected sibling were homozygous for this deletion.     

Harlequin ichthyosis (ichq): a juvenile lethal mouse mutation with ichthyosiform dermatitis.

The harlequin ichthyosis (ichq) mouse mutation arose spontaneously in 1989 in a colony of BALB/cJ mice at The Jackson Laboratory. Affected mice developed thick skin due to formation of compact, orthokeratotic scales that fractured over articular surfaces, secondary to bending. Harlequin ichthyosis mice on the inbred BALB/cJ background died between 9 and 12 days of age. Onset of the clinical phenotype corresponded with emergence of hair fibers from follicles at 5 days of age. There was marked proliferation of the root sheaths of anagen hair follicles, limited to the region within the dermis. Sebaceous glands were present but small compared with those of littermate controls. Emerging hair fibers were surrounded by a thick, compact sheath of cornified cells. Mutant skin contained large mitochondria with lamellar-shaped, electron-dense structures at the ultrastructural level. Keratohyalin granules were smaller and less pleomorphic than those in control mice. Lamellar bodies were not evident in either mutant or littermate control mice. Using a panel of antibodies to evaluate changes in keratinocyte differentiation, mouse-specific keratin 6 was overexpressed in the suprabasilar, hyperplastic epidermis. Loricrin expression, within the cytoplasm of cells in the stratum granulosum, decreased rapidly postmortem, unlike that in normal mice where it was stable for over 24 hours postmortem. Filaggrin expression, within granules of cells in the stratum granulosum, was prominent, corresponding to hypergranulosis evident by light microscopy in mutant mouse skin. Skin grafts from harlequin ichthyosis mice grafted onto immunodeficient nude mice maintained the phenotype for the 10-week observation period. The mutant gene locus mapped to the proximal end of mouse chromosome 19 and is inherited as a fully penetrant autosomal recessive gene. The harlequin ichthyosis mouse mutation is very similar to human type 2 harlequin ichthyosis for which it may be a good model.     

A novel long-QT 5 gene mutation in the C-terminus (V109I) is associated with a mild phenotype

Mutations in the human minK gene KCNE1 have been linked to autosomal dominant and autosomal recessive long-QT (LQT) syndrome, a cardiac condition predisposing to ventricular arrhythmias. minK and KvLQT1, the LQT1 gene product, form a native cardiac K+ channel that regulates the slowly delayed rectifier potassium current I(Ks). We used single-strand conformation polymorphism and sequencing techniques to identify novel KCNE1 mutations in patients with a congenital LQT syndrome of unknown genetic origin. In 150 unrelated index patients a missense mutation (V109I) was identified that significantly reduced the wild-type I(Ks) current amplitude (by 36%) when coexpressed with KvLQT1 in Xenopus oocytes. Other biophysical properties of the I(Ks) channel were not altered. Since we observed incomplete penetrance (only one of two mutation carriers could be diagnosed by clinical criteria), and the family's history was unremarkable for sudden cardiac death, the 109I allele most likely causes a mild phenotype. This finding may have implications for the occurrence of "acquired" conditions for ventricular arrhythmias and thereby the potential cardiac risk for asymptomatic mutation carriers still remains to be determined.     

A novel mutation in the FcgammaRIIIA gene (CD16) results in active natural killer cells lacking CD16

We report a novel mutation in FcgammaRIIIA (the transmembrane-form CD16) on natural killer (NK) cells in a patient with polyneuropathy. She had no history of recurrent infections. Her NK cells expressed no detectable CD16; however, her NK cytotoxic activity was normal, suggesting that CD16 expression and cytotoxic activity are independent of one another. Molecular analysis revealed a deletion of a single adenine base in exon 4 of CD16 at nucleotide 550. This deletion generates a STOP codon in an extra-cellular domain of the FcgammaRIIIA gene, thereby truncating the CD16 molecule. The patient's NK cells were not recognized by the anti-CD16 monoclonal antibodies 3G8 and Leu11c. Whether the development of her polyneuropathy is associated with this novel mutation is unclear.     

Type III bare lymphocyte syndrome associated with a novel RFXAP mutation: a case report

Type III bare lymphocyte syndrome (BLS) is a severe combined immunodeficiency disease caused by the absence of MHC Class II expression associated with low expression of class I molecules. Here, we report a case with type III BLS who lacked RFXAP (Regulatory factor X-associated protein) expression as a result from a novel mutation introducing a premature stopcodon in DE-region at amino acid 73.