A novel homozygous missense mutation in PNPLA2 in a patient manifesting primary triglyceride deposit cardiomyovasculopathy

Primary triglyceride deposit cardiomyovasculopathy (P-TGCV), caused by a rare genetic mutation in PNPLA2 encoding adipose triglyceride lipase (ATGL), exhibits severe cardiomyocyte steatosis and heart failure. Here, we report the case of a 51-year-old man with P-TGCV homozygous for a novel PNPLA2 mutation (c.446C > G, P149R) in the catalytic domain of ATGL. Analyses of endomyocardial biopsy specimens and in vitro expression experiments showed mutant protein expression with conserved lipid binding, but reduced lipolytic activity, indicating mutation pathogenicity.

Methods of calculating 123I-β-methyl-P-iodophenyl-pentadecanoic acid washout rates in triglyceride deposit cardiomyovasculopathy

Objective

This study aimed to optimize various methods of calculating washout rates (WRs) of ¹²³I-β-methyl-p-iodophenyl-pentadecanoic (BMIPP), as they are essential to diagnose triglyceride deposit cardiomyovasculopathy (TGCV) which is a rare disease entity identified in Japan and has been encoded in Orphanet (ORPHA code 565612).

Methods

We calculated WRs of ¹²³I-BMIPP from early (20 min) and delayed (200 min) images. We evaluated six methods of calculating WRs to discriminate TGVC patients (age, 56.8 ± 14.6 y; male, n = 13; female, n = 4) and 21 ¹²³I-BMIPP studies were involved including 4 follow-up studies. Washout rates were calculated by two planar methods using anterior images with cardiac and background regions of interest (ROIs) and by four SPECT methods using either array and polar plots or summed short-axis images. The final diagnoses of TGCV were confirmed according to the 2020 diagnostic criteria, and the diagnostic accuracy of WRs calculated using the six methods was analyzed using the area under receiver-operating characteristics curves (ROC-AUC). Multiple scatter-plot matrix methods were evaluated with correlations for comparison.

Results

All six methods were useful for diagnosis and did not significantly differ. The four SPECT methods showed excellent diagnostic accuracy (AUC 1.0), whereas the planar methods with and without background correction could be acceptable (AUC 0.857 and 0.964, respectively). The WRs were relatively lower for patients with CAD and remarkable metabolic defects than for patients with TGCV but without defects.

Conclusions

For the diagnosis of TGCV, the WR cutoff of 10% of ¹²³I-BMIPP functioned well in planar and SPECT discrimination based on computational methods as a classifier. However, calculation optimization should improve TGCV diagnoses.

Clinical significance of 123I-BMIPP washout rate in patients with uncertain chronic heart failure

BACKGROUND

Recently, triglyceride deposit cardiomyovasculopathy (TGCV) with defective intracellular lipolysis was found to be a disease that causes heart failure. As a diagnostic criterion for TGCV, an Iodaine-123-β-methyl iodophenyl-pentadecanoic acid washout rate (BMIPP WOR) of < 10% is used, but its clinical significance in patients with heart failure remains to be clarified.

METHODS

In 62 hospitalized patients with chronic heart failure, ¹²³I-BMIPP myocardial single-photon emission computed tomography (SPECT) was performed predischarge state. The prevalence of TGCV was investigated. Subsequently, follow-up was conducted for ≥ 90 days (mean: 724.6 ± 392.7 days), and the association between the BMIPP WOR and cardiac events was examined, establishing all-cause mortality and admission due to heart failure as endpoints.

RESULTS

Of the 62 patients, the WOR was < 10% in 41 (66.1%). Of these, 26 (41.9%) were diagnosed with definite TGCV. Furthermore, cardiac events were noted in 12 patients (19.4%). Analysis with Cox proportional hazards models showed that the BMIPP WOR < 4.5% was a significant event-predicting factor [HR 4.29, 95% CI: 1.20-16.87; p = 0.0245]. On a Kaplan-Meier curve, the WOR was 4.5%; there was a significant difference in the incidence of events (p = 0.0298).

CONCLUSION

In the predischarge state of heart failure, ¹²³I-BMIPP myocardial SPECT was performed. In approximately 40% of the patients, a diagnosis of TGCV was made. The results suggested that the BMIPP WOR is useful for predicting the prognosis of chronic heart failure patients regardless of TGCV.

123I-BMIPP Scintigraphy Shows That CNT-01 (Tricaprin) Improves Myocardial Lipolysis in Patients with Idiopathic Triglyceride Deposit Cardiomyovasculopathy: First Randomized Controlled, Exploratory Trial for TGCV

Background: Triglyceride deposit cardiomyovasculopathy (TGCV) is a rare intractable cardiovascular disorder (Orphanet ORPHAcode: 565612) in which defective intracellular lipolysis results in heart failure and coronary artery disease. Myocardial scintigraphy with ¹²³I-β-methyl-p-iodophenylpentadecanoic acid (BMIPP) is useful to evaluate myocardial TG metabolism; its washout rate (WR) reflects myocardial lipolysis. This study reports the effects of CNT-01 (tricaprin), a developing orphan drug to facilitate lipolysis, on BMIPP-WR in patients with TGCV. Methods: An investigator-initiated, multicenter, randomized, double-blind exploratory, trial (Phase IIa) was conducted (UMIN000035403). Seventeen patients with idiopathic TGCV were orally administered 1.5 g/day of CNT-01 or placebo for 8 weeks. Endpoints included delta BMIPP-WR and clinical parameters such as 6-minwalk distance and TGCV severity score. Results: During the protocol, delta BMIPP-WRs were -0.26±3.28 and 7.08±3.28% (95% confidence intervals, -7.36 to 6.84 and -0.01 to 14.18) in the placebo and CNT-01 groups, respectively. The baseline-adjusted difference of delta BMIPP-WR between the two groups was significant (p=0.035) after one patient was excluded from the placebo group because of pseudonormalization of BMIPP-WR related to coronary bypass graft stenosis. Clinical parameters did not show significant changes. Conclusions: This study proved the mechanism of CNT-01 to improve myocardial lipolysis in TGCV, as demonstrated by BMIPP scintigraphy.

Neutral Lipid Storage Disease Associated with the PNPLA2 Gene: Case Report and Literature Review

Mutations in the PNPLA2 gene cause neutral lipid storage disease with myopathy (NLSDM) or triglyceride deposit cardiomyovasculopathy. We report a detailed case study of a 53-year-old man with NLSDM. The PNPLA2 gene was analyzed according to the reported method. We summarized the clinical, laboratory, and genetic information of 56 patients, including our patient and 55 other reported patients with homozygous or compound heterozygous mutations in the PNPLA2 gene. We found a novel homozygous mutation (c.194delC) in the PNPLA2 gene that resulted in frameshift. The patient suffered from normal-tension glaucoma and pulmonary cysts, symptoms that are relatively common in the elderly but were not previously reported for this disease. Our summary confirmed that Jordan's anomaly, polymorphonuclear leukocytes with lipid accumulation, was the most consistent finding of this disease. Because this disease is potentially treatable, our results may help rapid and correct diagnosis.

Newly developed selective immunoinactivation assay revealed reduction in adipose triglyceride lipase activity in peripheral leucocytes from patients with idiopathic triglyceride deposit cardiomyovasculopathy

Triglyceride deposit cardiomyovasculopathy (TGCV) is a rare and newly identified disease among patients requiring cardiac transplantation. TGCV is characterized by cardiomyocyte steatosis and triglyceride (TG)-deposit atherosclerosis, resulting from the abnormal intracellular metabolism of TG. TGCV is classified into primary and idiopathic types. Primary TGCV carries ultra-rare genetic mutations in the adipose triglyceride lipase (ATGL), a rate-liming enzyme that hydrolyzes intracellular TG in adipose and non-adipose tissues. Idiopathic TGCV, first identified among autopsied individuals with diabetes mellitus (DM) with severe heart diseases, shows no ATGL mutations and its causes and underlying mechanisms are still unknown. TGCV is difficult to diagnose in daily clinics, thereby demanding feasible diagnostic procedures. We aimed to develop an assay to measure ATGL activity using peripheral leucocytes. Human his6-ATGL was expressed in COS1 cells, purified to homogeneity, and used to raise a polyclonal antibody neutralizing TG-hydrolyzing activity of ATGL. We developed a selective immunoinactivation assay (SIIA) for the quantitation of ATGL activity in cell lysates of leucocytes by the antibody neutralizing ATGL activities. ATGL activity was measured in 13 idiopathic TGCV patients, with two patients with primary TGCV as the negative control. Healthy (non-DM) and DM controls without heart diseases were also subjected. The developed SIIA assay revealed significant reduction in ATGL activity in leucocytes from patients with idiopathic TGCV who did not carry ATGL mutations as compared with non-DM and DM controls. Thus, ATGL in leucocytes may be an important biomarker for the diagnosis of TGCV and our assay may provide insights into pathophysiology and elucidate the underlying mechanism of TGCV and related disorders.

Peripheral leukocyte anomaly detected with routine automated hematology analyzer sensitive to adipose triglyceride lipase deficiency manifesting neutral lipid storage disease with myopathy/triglyceride deposit cardiomyovasculopathy

Adipose triglyceride lipase (ATGL) deficiency manifesting neutral lipid storage disease with myopathy/triglyceride deposit cardiomyovasculopathy presents distinct fat-containing vacuoles known as Jordans' anomaly in peripheral leucocytes. To develop an automatic notification system for Jordans' anomaly in ATGL-deficient patients, we analyzed circulatory leukocyte scattergrams on automated hematology analyzer XE-5000. The BASO-WX and BASO-WY values were found to be significantly higher in patients than those in non-affected subjects. The two parameters measured by automated hematology analyzer may be expected to provide an important diagnostic clue for homozygous ATGL deficiency.

Genetic mutations in adipose triglyceride lipase and myocardial up-regulation of peroxisome proliferated activated receptor-γ in patients with triglyceride deposit cardiomyovasculopathy

Adipose triglyceride lipase (ATGL, also known as PNPLA2) is an essential molecule for hydrolysis of intracellular triglyceride (TG). Genetic ATGL deficiency is a rare multi-systemic neutral lipid storage disease. Information regarding its clinical profile and pathophysiology, particularly for cardiac involvement, is still very limited. A previous middle-aged ATGL-deficient patient in our institute (Case 1) with severe heart failure required cardiac transplantation (CTx) and exhibited a novel phenotype, "Triglyceride deposit cardiomyovasculopathy (TGCV)". Here, we tried to elucidate molecular mechanism underlying TGCV. The subjects were two cases with TGCV, including our second case who was a 33-year-old male patient (Case 2) with congestive heart failure requiring CTx. Case 2 was homozygous for a point mutation in the 5' splice donor site of intron 5 in the ATGL, which results in at least two types of mRNAs due to splicing defects. The myocardium of both patients (Cases 1 and 2) showed up-regulation of peroxisome proliferated activated receptors (PPARs), key transcription factors for metabolism of long chain fatty acids (LCFAs), which was in contrast to these molecules' lower expression in ATGL-targeted mice. We investigated the intracellular metabolism of LCFAs under human ATGL-deficient conditions using patients' passaged skin fibroblasts as a model. ATGL-deficient cells showed higher uptake and abnormal intracellular transport of LCFA, resulting in massive TG accumulation. We used these findings from cardiac specimens and cell-biological experiments to construct a hypothetical model to clarify the pathophysiology of the human disorder. In patients with TGCV, even when hydrolysis of intracellular TG is defective, the marked up-regulation of PPARγ and related genes may lead to increased uptake of LCFAs, the substrates for TG synthesis. This potentially vicious cycle of LCFAs could explain the massive accumulation of TG and severe clinical course for this rare disease.