Volanesorsen and triglyceride levels in familial chylomicronemia syndrome: Long-term efficacy and safety data from patients in an open-label extension trial

BACKGROUND

Familial chylomicronemia syndrome (FCS) is a rare, autosomal recessive genetic disorder characterized by a marked increase in plasma triglyceride (TG) levels and recurrent episodes of pancreatitis. The response to conventional TG-lowering therapies is suboptimal. Volanesorsen, an antisense oligonucleotide that targets hepatic apoC-III mRNA, has been shown to significantly reduce TGs in patients with FCS.

OBJECTIVE

To further evaluate the safety and efficacy of extended treatment with volanesorsen in patients with FCS.

METHODS

This phase 3 open-label extension study evaluated the efficacy and safety of extended treatment with volanesorsen in three groups of patients with FCS: Those who had previously received volanesorsen or placebo in the APPROACH and COMPASS studies, and treatment-naive patients not participating in either study. Key endpoints included change in fasting TG and other lipid measurements, and safety over 52 weeks.

RESULTS

Volanesorsen treatment resulted in sustained reductions in plasma TG levels in previously treated patients from the APPROACH and COMPASS studies. Volanesorsen-treated patients from the three populations studied had mean decreases in fasting plasma TGs from index study baseline to months 3, 6, 12 and 24 as follows: decreases of 48%, 55%, 50%, and 50%, respectively (APPROACH); decreases of 65%, 43%, 42%, and 66%, respectively (COMPASS); and decreases of 60%, 51%, 47%, and 46%, respectively (treatment-naive). Common adverse events were injection site reactions and platelet count decrease, consistent with previous studies.

CONCLUSION

Extended open-label treatment with volanesorsen in patients with FCS resulted in sustained reductions of plasma TG levels and safety consistent with the index studies.

Development of Antisense Oligonucleotide Gapmers for the Treatment of Dyslipidemia and Lipodystrophy

Although technological advances in molecular genetics over the last few decades have greatly expedited the identification of mutations in many genetic diseases, the translation of the genetic mechanisms into a clinical setting has been quite challenging, with a minimum number of effective treatments available. The advancements in antisense therapy have revolutionized the field of neuromuscular disorders as well as lipid-mediated diseases. With the approval of splice-switching antisense oligonucleotide (AO) therapy for nusinersen and eteplirsen for the treatment of spinal muscular atrophy (SMA) and Duchenne muscular dystrophy (DMD), several modified AOs are now being evaluated in clinical trials for the treatment of a number of disorders. In order to activate RNase H-mediated cleavage of the target mRNA, as well as to increase the binding affinity and specificity, gapmer AOs are designed that have a PS backbone flanked with the modified AOs on both sides. Mipomersen (trade name Kynamro), a 2'-O-methoxyethyl (MOE) gapmer, was approved by the Food and Drug Administration (FDA) for the treatment of homozygous familial hypercholesterolemia (HoFH) in 2013. Volanesorsen, another 20-mer MOE gapmer has shown to be successful in lowering the levels of triglycerides (TGs) in several lipid disorders and has received conditional approval in the European Union for the treatment of Familial chylomicronemia syndrome (FCS) in May 2019 following successful results from phase II/III clinical trials. This chapter focuses on the clinical applications of gapmer AOs for genetic dyslipidemia and lipodystrophy.

Disappearance of recurrent pancreatitis after splenectomy in familial chylomicronemia syndrome

BACKGROUND AND AIMS

Recurrent pancreatitis is a severe complication of familial chylomicronemia syndrome (FCS) mainly secondary to lipoprotein lipase deficiency. The mechanism and interindividual variability of pancreatitis in FCS are not fully understood, but abnormalities in the drainage system of pancreatic veins could be involved.

METHODS AND RESULTS

Two cases of typical FCS are described with a past history of recurrent pancreatitis that dramatically improved after splenectomy performed in both cases for reasons non-related to FCS.

CONCLUSIONS

These are the first reports of the disappearance of pancreatitis after splenectomy in FCS and they should be considered of anecdotal nature at this time. The disappearance of pancreatitis following splenectomy could be in part due to subsequent improvements in pancreatic drainage. Extrahepatic portal hypertension induced by hypertriglyceridemic splenomegaly leading to pancreatic congestion could also be a contributing factor.

Incidental finding of severe hypertriglyceridemia in children. Role of multiple rare variants in genes affecting plasma triglyceride

BACKGROUND

The incidental finding of severe hypertriglyceridemia (HyperTG) in a child may suggest the diagnosis of familial chylomicronemia syndrome (FCS), a recessive disorder of the intravascular hydrolysis of triglyceride (TG)-rich lipoproteins. FCS may be due to pathogenic variants in lipoprotein lipase (LPL), as well as in other proteins, such as apolipoprotein C-II and apolipoprotein A-V (activators of LPL), GPIHBP1 (the molecular platform required for LPL activity on endothelial surface) and LMF1 (a factor required for intracellular formation of active LPL).

OBJECTIVE

Molecular characterization of 5 subjects in whom HyperTG was an incidental finding during infancy/childhood.

METHODS

We performed the parallel sequencing of 20 plasma TG-related genes.

RESULTS

Three children with severe HyperTG were found to be compound heterozygous for rare pathogenic LPL variants (2 nonsense, 3 missense, and 1 splicing variant). Another child was found to be homozygous for a nonsense variant of APOA5, which was also found in homozygous state in his father with longstanding HyperTG. The fifth patient with a less severe HyperTG was found to be heterozygous for a frameshift variant in LIPC resulting in a truncated Hepatic Lipase. In addition, 1 of the patients with LPL deficiency and the patient with APOA-V deficiency were also heterozygous carriers of a pathogenic variant in LIPC and LPL gene, respectively, whereas the patient with LIPC variant was also a carrier of a rare APOB missense variant.

CONCLUSIONS

Targeted parallel sequencing of TG-related genes is recommended to define the molecular defect in children presenting with an incidental finding of HyperTG.

Clinical and genetic features of 3 patients with familial chylomicronemia due to mutations in GPIHBP1 gene

BACKGROUND

Familial chylomicronemia is a recessive disorder that may be due to mutations in lipoprotein lipase (LPL) and in other proteins such as apolipoprotein C-II and apolipoprotein A-V (activators of LPL), GPIHBP1 (the molecular platform required for LPL activity on endothelial surface), and LMF1 (a factor required for intracellular formation of active LPL).

METHODS

We sequenced the familial chylomicronemia candidate genes in 2 adult females presenting long-standing hypertriglyceridemia and a history of acute pancreatitis.

RESULTS

Both probands had plasma triglyceride >10 mmol/L but no mutations in the LPL gene. The sequence of the other candidate genes showed that one patient was homozygous for a novel missense mutation p.(Cys83Arg), and the other was homozygous for a previously reported nonsense mutation p.(Cys 89*), respectively, in GPIHBP1. Family screening showed that the hypertriglyceridemic brother of the p.(Cys83Arg) homozygote was also homozygous for this mutation. He had no history of pancreatitis. The p.(Cys83Arg) heterozygous carriers had normal triglyceride levels. The substitution of a cysteine residue in the Ly6 domain of GPIHBP1 is predicted to abolish one of the disulfide bridges required to maintain the structure of GPIHBP1. The p.(Cys89*) mutation results in a truncated protein devoid of function.

CONCLUSIONS

Both mutant GPIHBP1 proteins are expected to be incapable of transferring LPL from the subendothelial space to the endothelial surface.