A case of apolipoprotein A-I deficiency due to carboxyl-terminal truncation

Apolipoprotein genetic variants and hereditary amyloidosis

PURPOSE OF REVIEW

Amyloidosis is caused by the deposition of misfolded aggregated proteins called amyloid fibrils that in turn cause organ damage and dysfunction. In this review, we aim to summarize the genetic, clinical, and histological findings in apolipoprotein-associated hereditary amyloidosis and the growing list of mutations and apolipoproteins associated with this disorder. We also endeavor to summarize the features of apolipoproteins that have led them to be overrepresented among amyloidogenic proteins. Additionally, we aim to distinguish mutations leading to amyloidosis from those that lead to inherited dyslipidemias.

RECENT FINDINGS

Apolipoproteins are becoming increasingly recognized in hereditary forms of amyloidosis. Although mutations in APOA1 and APOA2 have been well established in hereditary amyloidosis, new mutations are still being detected, providing further insight into the pathogenesis of apolipoprotein-related amyloidosis. Furthermore, amyloidogenic mutations in APOC2 and APOC3 have more recently been described. Although no hereditary mutations in APOE or APOA4 have been described to date, both protein products are amyloidogenic and frequently found within amyloid deposits.

SUMMARY

Understanding the underlying apolipoprotein mutations that contribute to hereditary amyloidosis may help improve understanding of this rare but serious disorder and could open the door for targeted therapies and the potential development of new treatment options.

The brave new world of genetic testing in the management of the dyslipidaemias

PURPOSE OF REVIEW

With the exception of familial hypercholesterolaemia, the value of genetic testing for managing dyslipidaemias is not established. We review the genetics of major dyslipidaemias in context of clinical practice.

RECENT FINDINGS

Genetic testing for familial hypercholesterolaemia is valuable to enhance diagnostic precision, cascade testing, risk prediction and the use of new medications. Hypertriglyceridaemia may be caused by rare recessive monogenic, or by polygenic, gene variants; genetic testing may be useful in the former, for which antisense therapy targeting apoC-III has been approved. Familial high-density lipoprotein deficiency is caused by specific genetic mutations, but there is no effective therapy. Familial combined hyperlipidaemia (FCHL) is caused by polygenic variants for which there is no specific gene testing panel. Familial dysbetalipoproteinaemia is less frequent and commonly caused by APOE ε2ε2 homozygosity; as with FCHL, it is responsive to lifestyle modifications and statins or/and fibrates. Elevated lipoprotein(a) is a quantitative genetic trait whose value in risk prediction over-rides genetic testing; treatment relies on RNA therapeutics.

SUMMARY

Genetic testing is not at present commonly available for managing dyslipidaemias. Rapidly advancing technology may presage wider use, but its worth will require demonstration of cost-effectiveness and a healthcare workforce trained in genomic medicine.

Inborn errors of apolipoprotein A-I metabolism: implications for disease, research and development

PURPOSE OF REVIEW

We review current knowledge regarding naturally occurring mutations in the human apolipoprotein A-I (APOA1) gene with a focus on their clinical complications as well as their exploitation for the elucidation of structure-function-(disease) relationships and therapy.

RECENT FINDINGS

Bi-allelic loss-of-function mutations in APOA1 cause HDL deficiency and, in the majority of patients, premature atherosclerotic cardiovascular disease (ASCVD) and corneal opacities. Heterozygous HDL-cholesterol decreasing mutations in APOA1 were associated with increased risk of ASCVD in several but not all studies. Some missense mutations in APOA1 cause familial amyloidosis. Structure-function-reationships underlying the formation of amyloid as well as the manifestion of amyloidosis in specific tissues are better understood. Lessons may also be learnt from the progress in the treatment of amyloidoses induced by transthyretin variants. Infusion of reconstituted HDL (rHDL) containing apoA-I (Milano) did not cause regression of atherosclerosis in coronary arteries of patients with acute coronary syndrome. However, animal experiments indicate that rHDL with apoA-I (Milano) or apoA-I mimetic peptides may be useful for the treatment of heart failure of inflammatory bowel disease.

SUMMARY

Specific mutations in APOA1 are the cause of premature ASCVD or familial amyloidosis. Synthetic mimetics of apoA-I (mutants) may be useful for the treatment of several diseases beyond ASCVD.

Rare dyslipidaemias, from phenotype to genotype to management: a European Atherosclerosis Society task force consensus statement

Genome sequencing and gene-based therapies appear poised to advance the management of rare lipoprotein disorders and associated dyslipidaemias. However, in practice, underdiagnosis and undertreatment of these disorders are common, in large part due to interindividual variability in the genetic causes and phenotypic presentation of these conditions. To address these challenges, the European Atherosclerosis Society formed a task force to provide practical clinical guidance focusing on patients with extreme concentrations (either low or high) of plasma low-density lipoprotein cholesterol, triglycerides, or high-density lipoprotein cholesterol. The task force also recognises the scarcity of quality information regarding the prevalence and outcomes of these conditions. Collaborative registries are needed to improve health policy for the care of patients with rare dyslipidaemias.