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Biomedical subjects

H E Henderson

Publications and source records attributed to H E Henderson.

At least 19 recordsLinked to original sources
PubMed2006

An OTC deficiency 'phenocopy' in association with Klinefelter syndrome.

Late-onset urea cycle disorder in a 20-month-old boy is unusually associated with Klinefelter syndrome with a 47XXY karyotype. We record the typical clinical and biochemical findings of ornithine transcarbamylase (OTC) deficiency in a young boy with a short history of recurrent vomiting, self mutilating behaviour, lethargy, ataxia and seizures. Laboratory studies showed hyperammonaemia and orotic aciduria, with normal citrulline and other urea cycle amino acids. Unfortunately, a liver biopsy for OTC activity measurement was refused by the parents. A rapid reversal of phenotype was seen on the introduction of a low-protein diet with accompanying benzoate and phenylbutyrate administration. Linkage studies suggested the inheritance of two X chromosomes, which was confirmed by karyotype analysis. Sequencing of all exons and immediate splice site regions revealed no sequence alterations in these sections of the OTC gene. A search for skewing of X-inactivation in the liver was not possible but we did show a random pattern of X-inactivation in leukocytes. The possibility of maternal X chromosome iso-disomy in our patient was discounted by microsatellite analysis, which revealed the inheritance of two independent X chromosomes. Mutation analysis in the OTC gene has shown that approximately 20% of patients with liver biopsy confirmed OTC deficiency do not have mutations in the coding or immediate splice-site sequences of this gene. Their classification as OTC phenocopies remains speculative, awaiting clarification of the underlying DNA alteration. We report on the novel association of OTC deficiency and Klinefelter syndrome with the additional interest of a probable unusual genetic defect underlying the OTC abnormality.

Chromosomes, Human, X↗
PubMed2002

Spinal muscular atrophy in black South Africans: concordance with the universal SMN1 genotype.

Only one study has reported on the genetic basis of spinal muscular atrophy (SMA) in South African subjects. This was conducted in the Johannesburg region and has suggested that black South Africans only (indigenous Africans) differ from the norm. We have explored this further by DNA studies in 30 unrelated and racially diverse patients who reside in the Western Cape, and who were assessed as SMA subjects according to the internationally accepted inclusion criteria for SMA. These subjects were seen at the neurology clinic at Red Cross Children's Hospital in Cape Town during the period 1980-2001. Four had the type 1 form of SMA, 16 had type 2 and 10 had type 3. All patients were found to be homozygous for the loss of either exon 7 or exons 7 and 8 of the SMN1 gene. Six additional patients had anterior horn cell disease but were negative for the SMN1 gene deletion. All six had exclusion features listed in the international guidelines. This study shows that all patients from the Western Cape, which included 12 black South Africans, are no different genetically or phenotypically from the internationally recognized form of typical SMA.

Black People↗
PubMed2000

X-linked agammaglobulinaemia and the underlying genetics in two kindreds.

OBJECTIVE: Molecular analysis of the Bruton's tyrosine kinase (Btk) gene in two unrelated families, with a combined total of seven boys, affected by X-linked agammaglobulinaemia (XLA). METHODS: Protein electrophoresis and western blotting were used for the examination of Btk protein synthesis in blood leucocytes. Isolation of the coding sequence of the Btk gene was performed by amplification using the reverse transcription-polymerase chain reaction (RT-PCR) technique. Sequence alterations were screened for by the single-stranded conformation polymorphism (SSCP) method and characterized by standard sequencing protocols. RESULTS: Western blotting revealed Btk protein to be absent in leucocytes of affected males from both families. A novel 3 b.p. deletion in exon 3 of the Btk gene was found to be responsible for the XLA phenotype in the affected proband in one family (kindred I). A diagnostic PCR assay was established to detect this mutation in other affected male siblings and carrier females. For the second family (kindred II), the coding sequence of the Btk gene and the promoter region were found to be normal. CONCLUSIONS: The present study has demonstrated genetic heterogeneity in the Btk gene in South African XLA patients and has identified a novel mutation in this gene in the largest of the affected kindreds. The gene mutation in the second kindred was undetermined and may be indicative of a defect in some other gene associated with Btk function or stability. Western blotting was found to be informative in establishing a deficiency of Btk protein in both probands and is recommended as a frontline procedure in the molecular diagnosis and work-up of XLA.

Agammaglobulinemia↗
PubMed2000

Plasma and vessel wall lipoprotein lipase have different roles in atherosclerosis.

Lipoprotein lipase (LPL) is a key enzyme in lipoprotein metabolism, and has been hypothesized to exert either pro- or anti-atherogenic effects, depending on its localization. Decreased plasma LPL activity is associated with the high triglyceride (TG);-low HDL phenotype that is often observed in patients with premature vascular disease. In contrast, in the vessel wall, decreased LPL may be associated with less lipoprotein retention due to many potential mechanisms and, therefore, decreased foam cell formation. To directly assess this hypothesis, we have distinguished between the effects of variations in plasma and/or vessel wall LPL on atherosclerosis susceptibility in apoE-deficient mice. Reduced LPL in both plasma and vessel wall (LPL(+/-)E(-/-)) was associated with increased TG and increased total cholesterol (TC) compared with LPL(+/+)E(-/-) sibs. However despite their dyslipidemia, LPL(+/-)E(-/-) mice had significantly reduced lesion areas compared to the LPL(+/+)E(-/-) mice. Thus, decreased vessel wall LPL was associated with decreased lesion formation even in the presence of reduced plasma LPL activity. In contrast, transgenic mice with increased plasma LPL but with no increase in LPL expression in macrophages, and thus the vessel wall, had decreased TG and TC and significantly decreased lesion areas compared with LPL(+/+)E(-/-) mice. This demonstrates that increased plasma LPL activity alone, in the absence of an increase in vessel wall LPL, is associated with reduced susceptibility to atherosclerosis. Taken together, these results provide in vivo evidence that the contribution of LPL to atherogenesis is significantly influenced by the balance between vessel wall protein (pro-atherogenic) and plasma activity (anti-atherogenic).

Animals↗
PubMed1999

Lipid and lipoprotein analysis of cats with lipoprotein lipase deficiency.

BACKGROUND: We have previously described a colony of domestic cats with a naturally occurring mutation in the lipoprotein lipase (LPL) gene. We have now further characterized cats homozygous for LPL deficiency (LPL -/-, homozygotes), and have contrasted these with heterozygotes (LPL +/-) and normal cats (LPL +/+). MATERIALS AND METHODS: Density gradient ultracentrifugation with subsequent lipid analysis, agarose and polyacrylamide gel electrophoresis was used to examine detailed liproprotein differences between the genotypes. Oral fat loading studies and breast milk fatty acid analysis were also performed to further characterize the phenotypic expression of LPL deficiency in this model system. RESULTS: Several lipid abnormalities associated with homozygosity for LPL deficiency were evident. Triglyceride-rich lipoprotein-triglycerides (TRL-TG) and cholesterol (TRL-C) were higher (TRL-TG 2.09 +/- 1.14 vs. 0.15 +/- 0.04 mmol L-1, P < 0.001; TRL-C 0.42 +/- 0.30 vs. 0.11 +/- 0.16 mmol L-1, P < 0.05) in male -/- than in male +/+ cats, as was HDL-cholesterol (HDL-C, 1.75 +/- 0.24 vs. 1.41 +/- 0.14 mmol L-1, P < 0.05). LDL-C levels were lower in homozygous cats than in control cats, similar to what is seen in human LPL deficiency. Oral fat loading studies revealed that homozygous cats have a marked reduced ability to clear plasma TGs in terms of peak time (7 h vs. 3 h), peak height (9.36 vs. 1.1 mmol L-1), area under the TG clearance curve (AUC, 280.3 vs. 2.2 h mmol L-1) and time to return to baseline. Fasting lipid and lipoprotein levels were not significantly different between heterozygous and normal cats. However, oral fat loading in heterozygotes revealed an intermediate phenotype (peak of 2.35 mmol L-1 at 5 h, AUC 13.1 h mmol L-1), highlighting the impaired TG clearance in these animals. CONCLUSION: Thus, LPL deficiency in the cat results in a lipid and lipoprotein phenotype that predominantly parallels human LPL deficiency, further validating the use of these animals in studies on the pathobiology of LPL.

Animals↗
PubMed1999

Lipoprotein lipase activity is decreased in a large cohort of patients with coronary artery disease and is associated with changes in lipids and lipoproteins.

Lipoprotein lipase (LPL) is crucial in the hydrolysis of triglycerides (TG) in TG-rich lipoproteins in the formation of HDL particles. As both these lipoproteins play an important role in the pathogenesis of atherosclerotic vascular disease, we sought to assess the relationship between post-heparin LPL (PH-LPL) activity and lipids and lipoproteins in a large, well-defined cohort of Dutch males with coronary artery disease (CAD). These subjects were drawn from the REGRESS study, totaled 730 in number and were evaluated against 75 healthy, normolipidemic male controls. Fasting mean PH-LPL activity in the CAD subjects was 108 46 mU/ml, compared to 138 44 mU/ml in controls (P < 0.0001). When these patients were divided into activity quartiles, those in the lowest versus the highest quartile had higher levels of TG (P < 0.001), VLDLc and VLDL-TG (P = 0.001). Conversely, levels of TC, LDL, and HDLc were lower in these patients (P = 0.001, P = 0.02, and P = 0.001, respectively). Also, in this cohort PH-LPL relationships with lipids and lipoproteins were not altered by apoE genotypes. The frequency of common mutations in the LPL gene associated with partial LPL deficiency (N291S and D9N carriers) in the lowest quartile for LPL activity was more than double the frequency in the highest quartile (12.0% vs. 5.0%; P = 0.006). By contrast, the frequency of the S447X LPL variant rose from 11.5% in the lowest to 18.3% (P = 0.006) in the highest quartile. This study, in a large cohort of CAD patients, has shown that PH-LPL activity is decreased (22%; P = 0.001) when compared to controls; that the D9N and N291S, and S447X LPL variants are genetic determinants, respectively, in CAD patients of low and high LPL PH-LPL activities; and that PH-LPL activity is strongly associated with changes in lipids and lipoproteins.

Adult↗
PubMed1998

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.

Adult↗
PubMed1997

The apolipoprotein E2 (Arg145Cys) mutation causes autosomal dominant type III hyperlipoproteinemia with incomplete penetrance.

Type III hyperlipoproteinemia (type III HLP) is an atherogenic disorder of lipoprotein metabolism characterized by the accumulation of cholesterol-enriched VLDL and is usually associated with homozygosity for a normal variant of apoE, apoE2. ApoE2(Arg145Cys) is a rare variant arising from a C-->T transition at nucleotide 4031 and has been linked to type III HLP. Ten subjects from a group of 42 unrelated individuals with proven type III HLP were found to be either heterozygous or homozygous for the apoE2(Arg145Cys) mutation by DNA sequencing. The apoE4-Philadelphia (Glu13Lys, Arg145Cys) variant was subsequently excluded. None of 4 homozygotes (3 blacks and 1 of mixed ancestry) developed ischemic heart disease, but they did present with xanthomata. In contrast, 6 heterozygous subjects presented mainly with ischemic heart disease but generally lacked physical signs. Cholesterol concentrations ranged from 6.2 mmol/L to 13.3 mmol/L and triglyceride levels from 3.2 to 13.2 mmol/L. The dyslipoproteinemia in homozygous and heterozygous subjects was indistinguishable. Family investigation identified an additional 10 heterozygous mutant-allele carriers, of whom 3 had type III HLP. This unique cohort of patients indicates that the apoE2(Arg145Cys) mutation is relatively common in several population groups in our region and may be particularly prevalent in blacks. There was no clear allele dosage effect present for the development of dyslipoproteinemia or atherosclerosis. The mode of inheritance is for the first time clearly established to be autosomal dominant with incomplete penetrance.

Adolescent↗
PubMed1996

A new mutation destroying disulphide bridging in the C-terminal domain of lipoprotein lipase.

Lipoprotein lipase (LPL) is one of two intravascular lipases involved in the lipolysis of the triglyceride core of circulating lipoproteins. The occurrence of patients with genetic deficiencies has provided insight into the structure and function relationships of this lipase. It is now known that LPL manifests a two domain structure with the N-terminal domain of greater structural and functional significance as it contains the active site and interfacial binding motifs. We report on a Cys418Tyr substitution in the C-terminal domain which disrupts the only disulphide bridge in the region and is associated with catalytic deficiency in post-heparin plasma. This result was unexpected as previous in vitro assessment of the functional significance of disulphide bridging had shown that while the 3, N-terminal disulphides were critical for enzyme function, loss of the only C-terminal disulphide minimally affected catalytic activity. We generated the Cys418Tyr mutant by site-directed mutagenesis and show that it manifests 48% of normal activity in vitro, while the companion variants, Cys438Ser and Cys418Ser-Cys438Ser, are less affected with activities at 76% and 78% of normal.

Adult↗
PubMed1996

Alterations in plasma lipoproteins and apolipoproteins before the age of 40 in heterozygotes for lipoprotein lipase deficiency.

We have assessed the expression of heterozygosity for lipoprotein lipase (LPL) deficiency by studying a single large French Canadian family comprising 92 persons including 21 carriers of the catalytically defective P207L mutation. Phenotypic changes distinguishing heterozygotes from controls were seen early, before the age of 40 and often before 20 years of age. In the total cohort these changes included an elevation in the mean very low density (VLDL) and intermediate density lipoprotein (IDL) triglyceride (+69%; P = 0.01 and +40%; P = 0.001) and cholesterol (+51%; P = 0.03 and +67%; P = 0.007) and apoB levels but decreased HDL2 and HDL3 cholesterol, (-32%; P = 0.01 and -15%; P = 0.002 respectively). While the lipid compositions of VLDL and IDL were similar between heterozygotes and controls, the low density (LDL) and high density lipoproteins (HDL) of carriers were triglyceride enriched. Heterozygotes also had a markedly lower apoC-III ratio (apoC-III in supernatant/apoC-III in heparin precipitate) (1.46 vs. 3.86 P = 1 x 10(-4)) indicating a substantial enrichment of VLDL and IDL with apoC-III and depletion of HDL apoC-III supporting this ratio as an effective index for efficiency of lipolysis. LpA-I was markedly reduced (0.34 vs. 0.43 P = 1 x 10(-5)) showing that levels of this particle are partly dependent on LPL catalytic activity. Heterozygotes manifest from an early age with a markedly reduced HDL, LpA-I, apoC-III ratio and an increased TC/HDLc ratio which would predict a relatively increased risk of premature coronary artery disease, compared to their normal siblings.

Adult↗
PubMed1994

Mutagenesis in four candidate heparin binding regions (residues 279-282, 291-304, 390-393, and 439-448) and identification of residues affecting heparin binding of human lipoprotein lipase.

Lipoprotein lipase (LPL) interaction with membrane-associated polyanions is a critical component of normal catalytic function. Two strong candidate binding regions, rich in arginine and lysine residues, have been defined in the N-terminal domain (aa279-282 and aa292-304) that show homology to the heparin-binding consensus sequences -X-B-B-X-B-X- and -X-B-B-B-X-X-B-X-, respectively. Additional candidate regions appear in the C-terminal domain, (residues 390-393), which are homologous to the thrombospondin heparin-binding repeat, and the positively charged terminal decapeptide (residues 439-448). To determine residues and domains critical to heparin binding, we have generated different LPL mutants that have alanine substitutions of single arginine and lysine residues and sequence interchanges with the homologous hepatic (HL) and pancreatic (PL) lipases. The mutant cDNAs were expressed in COS-1 cells and catalytically active mutants were assessed for binding to heparin-Sepharose. All the alanine substitutions within the two regions homologous to the heparin-binding consensus sequences in the N-terminal domain either abolished activity or produced a lowering of heparin binding affinity. None of the mutants in the C-terminal domain of LPL showed a loss of activity or a reduction in heparin binding affinity. These data demonstrate that charged residues at positions 279-282 and 292-304 of LPL are important for heparin binding affinity whereas the residues 390-393 and 439-448 in the C-terminal domain are not involved in heparin binding.

Amino Acid Sequence↗
PubMed1993

Structure-function relationships of lipoprotein lipase: mutation analysis and mutagenesis of the loop region.

The molecular models of two microbial lipases and human pancreatic lipase (PL) have suggested the existence of common structural motifs including a buried active site shielded by an amphipathic surface loop. In an effort to explore the role of residues comprising the loop of lipoprotein lipase (LPL), we have used site-directed mutagenesis to generate three new LPL variants. In variant LPLM1 we deleted 18 amino acids leaving a loop of only 4 residues which resulted in an LPL protein inactive against triolein substrates. In contrast, two other LPL variants with only partial deletions, involving the apical section of the loop [LPLM2 (-8 amino acids) and LPLM3 (-2 amino acids)] manifested normal lipolytic activity. These findings indicate a critical requirement for the maintenance of charge and periodicity in the proximal and distal segments of the LPL loop in normal catalytic function. This is further highlighted by the detection of a mutation in the proximal section of the loop in a patient with LPL deficiency at position 225 which results in a substitution of threonine for isoleucine. The intact catalytic activity of the partial deletion variants (LPLM2 and LPLM3) further suggests that the apical residues of the loop contribute minimally to the functional motifs of the active site. We support this postulate by showing that the conserved glycine in the apical turn section (G229) can be substituted by glutamine, lysine, proline, or threonine without significantly affecting catalytic activity.

Base Sequence↗
PubMed1992

A missense mutation Pro157 Arg in lipoprotein lipase (LPLNijmegen) resulting in loss of catalytic activity.

Here we report on the molecular defect that leads to a deficiency of lipoprotein lipase (LPL) activity in a proband of Dutch descent. Southern-blot analysis of the LPL gene from the patient did not reveal any major DNA rearrangements. Sequencing of polymerase-chain-reaction-amplified DNA revealed that the proband is a homozygote for G725C, resulting in a substitution of Pro157 for Arg. This substitution alters a restriction site for PvuII, which allowed rapid identification of the mutant allele in family members. Site-directed mutagenesis and transient expression of the mutant LPL in COS cells produced an enzymatically inactive protein, establishing the functional significance of this mutation. This naturally occurring mutation which alters the Pro157 adjacent to Asp156 of the proposed catalytic triad, indicates that this region of the protein is indeed crucial for LPL catalytic activity.

Adult↗
PubMed1992

A missense mutation (Asp250----Asn) in exon 6 of the human lipoprotein lipase gene causes chylomicronemia in patients of different ancestries.

We have previously reported two common lipoprotein lipase (LPL) gene mutations underlying LPL deficiency in the majority of 37 French Canadians (Monsalve et al., 1990. J. Clin. Invest. 86: 728-734; Ma et al., 1991. N. Engl. J. Med. 324: 1761-1766). By examining the 10 coding exons of the LPL gene in another French Canadian patient, we have identified a third missense mutation that is found in two of the three remaining patients for whom mutations are undefined. This is a G to A transition in exon 6 that results in a substitution of asparagine for aspartic acid at residue 250. Using in vitro site-directed mutagenesis, we have confirmed that this mutation causes a catalytically defective LPL protein. In addition, the Asp250----Asn mutation was also found on the same haplotype in an LPL-deficient patient of Dutch ancestry, suggesting a common origin. This mutation alters a TaqI restriction site in exon 6 and will allow for rapid screening in patients with LPL deficiency.

Amino Acid Sequence↗
PubMed1992

The lipoprotein lipase Gly188----Glu mutation in South Africans of Indian descent: evidence suggesting common origins and an increased frequency.

Lipoprotein lipase (LPL) plays a crucial role in the hydrolysis of the triglyceride core of circulating chylomicrons and very low density lipoproteins (VLDL) and also has a major effect on the levels and lipid composition of high density lipoproteins (HDL). LPL deficiency is inherited as an autosomal recessive trait and most commonly presents with chylomicronaemia, abdominal pain, and eruptive xanthomata. We have previously described a mutation in exon 5 of the LPL gene which results in a substitution of glutamic acid for glycine at amino acid 188. We have now assessed 16 South African LPL deficient patients from nine separate kindreds for this mutation. Nine of these probands were homozygous for the mutation and were from four families, all of Indian descent. The ancestors of these probands have their origins in villages close to Bombay, India, which suggests a common ancestral mutation for the four Indian kindreds, particularly as the mutant allele in each family carried the identical restriction fragment length polymorphism (RFLP) haplotype. The presence of at least nine affected subjects in this small community around Cape Town is evidence for a higher than expected gene frequency for LPL deficiency in this population.

Base Sequence↗
PubMed1991

Deletion of two growth-factor repeats from the low-density-lipoprotein receptor accelerates its degradation.

The region of the low-density-lipoprotein (LDL) receptor showing sequence similarity to the epidermal-growth-factor (EGF) precursor is required for LDL binding and the acid-induced dissociation of ligand and receptor. We describe here a naturally occurring mutant LDL receptor, found in a patient with homozygous familial hypercholesterolaemia, which lacks the first two growth-factor-like repeats of the EGF-precursor-like ('homology') domain. The mutation in the receptor gene is a 2.5 kb deletion including exons 7 and 8. The molecular mass of the mutant receptor (145 kDa) was approx. 15 kDa smaller than the normal LDL receptor. The mutant receptors were derived from precursors (105 kDa) that apparently underwent normal processing. Fibroblasts from the patient had high-affinity binding sites for the the apolipoprotein E-containing ligand, beta VLDL, but did not bind LDL. In the presence of beta VLDL, receptors were rapidly degraded. The mutant receptors also displayed an abnormally rapid turnover, about four times faster than that of normal receptors, in the absence of ligand; this accelerated degradation accounted for the low level of expression of mutant receptors in up-regulated cells. These data support a role for the growth-factor-like repeats in the binding of LDL (but not beta VLDL) and in receptor recycling, and indicate that a normal rate of turnover of unoccupied receptors is dependent on the integrity of these segments of the protein.

Adolescent↗
PubMed1991

A mutation in the human lipoprotein lipase gene as the most common cause of familial chylomicronemia in French Canadians.

BACKGROUND: Lipoprotein lipase hydrolyzes the triglyceride core of chylomicrons and very-low-density lipoproteins and has a crucial role in regulating plasma lipoprotein levels. Deficiencies of lipoprotein lipase activity lead to aberrations in lipoprotein levels. Worldwide, the frequency of lipoprotein lipase deficiency is highest among French Canadians. We sought to determine the molecular basis of the disorder in this population. METHODS: The entire coding sequence of the lipoprotein lipase gene from one French Canadian patient was amplified by the polymerase chain reaction and sequenced. Exon 5 from 36 other French Canadian patients was amplified and analyzed by dot blot hybridization with allele-specific oligonucleotides. RESULTS: Sequence analysis revealed a missense substitution of leucine (CTG) for proline (CCG) at residue 207 in exon 5. This mutation was found on 54 of the 74 mutant alleles (73 percent) in the patients. Studies of site-directed in vitro mutagenesis have confirmed that this mutation generates inactive lipoprotein lipase and is the cause of lipoprotein lipase deficiency. CONCLUSIONS: We have identified a missense mutation at residue 207 of the lipoprotein lipase gene that is the most common cause of lipoprotein lipase deficiency in French Canadians. This mutation can be easily detected by dot blot analysis, providing opportunity for definitive DNA diagnosis of the disorder and identification of heterozygous carriers.

Base Sequence↗