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Severe hypertriglyceridemia in a patient heterozygous for a lipoprotein lipase gene allele with two novel missense variants.

Kassner U, Salewsky B, Wühle-Demuth M, Szijarto IA, Grenkowitz T, Binner P, März W, Steinhagen-Thiessen E, Demuth I - Eur. J. Hum. Genet. (2015)

Bottom Line: The variants result in the amino-acid exchanges p.(Lys434Asn) and p.(Gly436Arg).No further relevant mutations were found by direct sequencing of the genes for APOA5, APOC2, LMF1 and GPIHBP1.We conclude that heterozygosity for damaging mutations of LPL may be sufficient to produce severe hypertriglyceridemia and that chylomicronemia may be transmitted in a dominant manner, at least in some families.

View Article: PubMed Central - PubMed

Affiliation: Lipid Clinic, Charité-Universitätsmedizin Berlin, Berlin, Germany.

ABSTRACT
Rare monogenic hyperchylomicronemia is caused by loss-of-function mutations in genes involved in the catabolism of triglyceride-rich lipoproteins, including the lipoprotein lipase gene, LPL. Clinical hallmarks of this condition are eruptive xanthomas, recurrent pancreatitis and abdominal pain. Patients with LPL deficiency and severe or recurrent pancreatitis are eligible for the first gene therapy treatment approved by the European Union. Therefore the precise molecular diagnosis of familial hyperchylomicronemia may affect treatment decisions. We present a 57-year-old male patient with excessive hypertriglyceridemia despite intensive lipid-lowering therapy. Abdominal sonography showed signs of chronic pancreatitis. Direct DNA sequencing and cloning revealed two novel missense variants, c.1302A>T and c.1306G>A, in exon 8 of the LPL gene coexisting on the same allele. The variants result in the amino-acid exchanges p.(Lys434Asn) and p.(Gly436Arg). They are located in the carboxy-terminal domain of lipoprotein lipase that interacts with the glycosylphosphatidylinositol-anchored HDL-binding protein (GPIHBP1) and are likely of functional relevance. No further relevant mutations were found by direct sequencing of the genes for APOA5, APOC2, LMF1 and GPIHBP1. We conclude that heterozygosity for damaging mutations of LPL may be sufficient to produce severe hypertriglyceridemia and that chylomicronemia may be transmitted in a dominant manner, at least in some families.

No MeSH data available.


Related in: MedlinePlus

Sequence analysis of the LPL variants. (a–c) Segments of genomic DNA sequence from LPL exon 8 of the patient showing (a) the two heterozygous mutations, c.1302A>T and c.1306G>A, detected in the PCR product, (b) the wild-type sequence detected in about the half of the sequenced cloned PCR products and (c) the sequence carrying the two mutations as detected in the other half of the cloned PCR products. (d) Alignment of the LPL amino-acid sequences (single-letter code) from humans and domestic cats in the domain containing the two missense variations detected in the patient. The glycine (G) residue at position 436 and at position 439 mutated in our patient and the cat colony with LPL deficiency is highlighted in red (The alignment was based on UniProt sequences with accession numbers P0685 (human LPL) and P55031 (cat LPL).
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fig1: Sequence analysis of the LPL variants. (a–c) Segments of genomic DNA sequence from LPL exon 8 of the patient showing (a) the two heterozygous mutations, c.1302A>T and c.1306G>A, detected in the PCR product, (b) the wild-type sequence detected in about the half of the sequenced cloned PCR products and (c) the sequence carrying the two mutations as detected in the other half of the cloned PCR products. (d) Alignment of the LPL amino-acid sequences (single-letter code) from humans and domestic cats in the domain containing the two missense variations detected in the patient. The glycine (G) residue at position 436 and at position 439 mutated in our patient and the cat colony with LPL deficiency is highlighted in red (The alignment was based on UniProt sequences with accession numbers P0685 (human LPL) and P55031 (cat LPL).

Mentions: Direct DNA sequencing of the coding sequences of LPL, APOC2, APOA5, LMF1 and GBIHBP1 revealed two new sequence variants in exon 8 of the LPL gene (Figure 1a), whereas no sequence alterations were detected in the other investigated genes. The sequence variants, c.1302A>T and c.1306G>A, are both of the missense type and result in the amino-acid exchanges p.(Lys434Asn) and p.(Gly436Arg), respectively. To the best of our knowledge, neither of the sequence alterations were previously described in humans. Both mutations are located in the carboxy-terminal domain of the LPL protein, which is involved in binding to GPIHBP1, a capillary endothelial cell protein that provides a platform for LPL-mediated processing of chylomicrons.11 Evaluation of the new sequence alterations using ‘PolyPhen-2' indicated that both variants are ‘probably damaging', with scores of 0.966 (p.(Lys434Asn)) and 1.0 (p.(Gly436Arg)).12 Similarly, another analysis tool, ‘Mutation Taster', rated the two sequence alterations as ‘disease causing',13 suggesting compound heterozygosity for two LPL gene variants. We next ligated an LPL exon 8-specific PCR product generated from the patients DNA into the plasmid pCR2.1, transformed bacteria with the ligation product and sequenced the plasmid inserts from a total of 21 independent clones. Eleven of the plasmid inserts contained the wild-type LPL exon 8 sequence (Figure 1b), whereas the remaining ten plasmid inserts carried the exon 8 sequence with the two sequence alterations, c.1302A>T and c.1306G>A, side by side (Figure 1c). This indicated that the patient has two coexisting variations on the same LPL allele, the other allele is wild type.


Severe hypertriglyceridemia in a patient heterozygous for a lipoprotein lipase gene allele with two novel missense variants.

Kassner U, Salewsky B, Wühle-Demuth M, Szijarto IA, Grenkowitz T, Binner P, März W, Steinhagen-Thiessen E, Demuth I - Eur. J. Hum. Genet. (2015)

Sequence analysis of the LPL variants. (a–c) Segments of genomic DNA sequence from LPL exon 8 of the patient showing (a) the two heterozygous mutations, c.1302A>T and c.1306G>A, detected in the PCR product, (b) the wild-type sequence detected in about the half of the sequenced cloned PCR products and (c) the sequence carrying the two mutations as detected in the other half of the cloned PCR products. (d) Alignment of the LPL amino-acid sequences (single-letter code) from humans and domestic cats in the domain containing the two missense variations detected in the patient. The glycine (G) residue at position 436 and at position 439 mutated in our patient and the cat colony with LPL deficiency is highlighted in red (The alignment was based on UniProt sequences with accession numbers P0685 (human LPL) and P55031 (cat LPL).
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Related In: Results  -  Collection

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fig1: Sequence analysis of the LPL variants. (a–c) Segments of genomic DNA sequence from LPL exon 8 of the patient showing (a) the two heterozygous mutations, c.1302A>T and c.1306G>A, detected in the PCR product, (b) the wild-type sequence detected in about the half of the sequenced cloned PCR products and (c) the sequence carrying the two mutations as detected in the other half of the cloned PCR products. (d) Alignment of the LPL amino-acid sequences (single-letter code) from humans and domestic cats in the domain containing the two missense variations detected in the patient. The glycine (G) residue at position 436 and at position 439 mutated in our patient and the cat colony with LPL deficiency is highlighted in red (The alignment was based on UniProt sequences with accession numbers P0685 (human LPL) and P55031 (cat LPL).
Mentions: Direct DNA sequencing of the coding sequences of LPL, APOC2, APOA5, LMF1 and GBIHBP1 revealed two new sequence variants in exon 8 of the LPL gene (Figure 1a), whereas no sequence alterations were detected in the other investigated genes. The sequence variants, c.1302A>T and c.1306G>A, are both of the missense type and result in the amino-acid exchanges p.(Lys434Asn) and p.(Gly436Arg), respectively. To the best of our knowledge, neither of the sequence alterations were previously described in humans. Both mutations are located in the carboxy-terminal domain of the LPL protein, which is involved in binding to GPIHBP1, a capillary endothelial cell protein that provides a platform for LPL-mediated processing of chylomicrons.11 Evaluation of the new sequence alterations using ‘PolyPhen-2' indicated that both variants are ‘probably damaging', with scores of 0.966 (p.(Lys434Asn)) and 1.0 (p.(Gly436Arg)).12 Similarly, another analysis tool, ‘Mutation Taster', rated the two sequence alterations as ‘disease causing',13 suggesting compound heterozygosity for two LPL gene variants. We next ligated an LPL exon 8-specific PCR product generated from the patients DNA into the plasmid pCR2.1, transformed bacteria with the ligation product and sequenced the plasmid inserts from a total of 21 independent clones. Eleven of the plasmid inserts contained the wild-type LPL exon 8 sequence (Figure 1b), whereas the remaining ten plasmid inserts carried the exon 8 sequence with the two sequence alterations, c.1302A>T and c.1306G>A, side by side (Figure 1c). This indicated that the patient has two coexisting variations on the same LPL allele, the other allele is wild type.

Bottom Line: The variants result in the amino-acid exchanges p.(Lys434Asn) and p.(Gly436Arg).No further relevant mutations were found by direct sequencing of the genes for APOA5, APOC2, LMF1 and GPIHBP1.We conclude that heterozygosity for damaging mutations of LPL may be sufficient to produce severe hypertriglyceridemia and that chylomicronemia may be transmitted in a dominant manner, at least in some families.

View Article: PubMed Central - PubMed

Affiliation: Lipid Clinic, Charité-Universitätsmedizin Berlin, Berlin, Germany.

ABSTRACT
Rare monogenic hyperchylomicronemia is caused by loss-of-function mutations in genes involved in the catabolism of triglyceride-rich lipoproteins, including the lipoprotein lipase gene, LPL. Clinical hallmarks of this condition are eruptive xanthomas, recurrent pancreatitis and abdominal pain. Patients with LPL deficiency and severe or recurrent pancreatitis are eligible for the first gene therapy treatment approved by the European Union. Therefore the precise molecular diagnosis of familial hyperchylomicronemia may affect treatment decisions. We present a 57-year-old male patient with excessive hypertriglyceridemia despite intensive lipid-lowering therapy. Abdominal sonography showed signs of chronic pancreatitis. Direct DNA sequencing and cloning revealed two novel missense variants, c.1302A>T and c.1306G>A, in exon 8 of the LPL gene coexisting on the same allele. The variants result in the amino-acid exchanges p.(Lys434Asn) and p.(Gly436Arg). They are located in the carboxy-terminal domain of lipoprotein lipase that interacts with the glycosylphosphatidylinositol-anchored HDL-binding protein (GPIHBP1) and are likely of functional relevance. No further relevant mutations were found by direct sequencing of the genes for APOA5, APOC2, LMF1 and GPIHBP1. We conclude that heterozygosity for damaging mutations of LPL may be sufficient to produce severe hypertriglyceridemia and that chylomicronemia may be transmitted in a dominant manner, at least in some families.

No MeSH data available.


Related in: MedlinePlus