Hypertriglyceridemia (HTG), characterized by the accumulation of very low-density lipoproteins (VLDLs), chylomicrons (CMs), and their remnant particles, is a risk factor for cardiovascular diseases, and severe HTG predisposes to acute pancreatitis.1 The combinatorial effects of genetic and environmental factors (e.g., high carbohydrates, lipid-rich diets, aging, obesity, diabetes mellitus, excess alcohol intake, and pregnancy) causes severe HTG. Chylomicronemia is defined as the accumulation of chylomicrons. As monogenic chylomicronemia is considered to have a higher risk of pancreatitis than polygenic chylomicronemia,2 revealing the genetic bases and the clinical features indicative of monogenic chylomicronemia will help to establish a personalized strategy to manage chylomicronemia and prevent pancreatitis.

During normal pregnancy, plasma TG levels increase by 2-4 fold as a physiological response.3 In rare cases, plasma TG increases severely, which could lead to pancreatitis and cause adverse or fatal events to both mother and fetus. Treatment options may include n-3 polyunsaturated fatty acids, fibrates, insulin, or plasma exchange,4,5 but their use is limited during pregnancy. Early diagnosis and adequate dietary management are essential to prevent severe HTG.

Here we report a case of childhood-onset occasional HTG with good adherence to dietary fat restriction who later developed gestational HTG-induced acute pancreatitis. Exome sequencing revealed a novel homozygous nonsense variant in the LMF1 gene, encoding lipase maturation factor 1 (LMF1) protein that is required for the proper folding and maturation of lipoprotein lipase (LPL). The implementation of strict dietary fat restriction reduced plasma TG levels and led to successful delivery.

All procedures were approved by the human genome and gene analysis research ethics committee of the University of Tokyo. The study was performed in line with The Code of Ethics of the World Medical Association (Declaration of Helsinki) after obtaining informed consent from the patient.

A 35-year-old woman at 32 weeks of gestation presented to the emergency room with sudden abdominal pain and was diagnosed with acute pancreatitis. At the visit, her serum TG level was markedly high at 10,500 mg/dL. Past medical history revealed that she was diagnosed with HTG (ca. 2,000 mg/dL) at eight years old. Since then, she has been on a fat restriction diet, and her TG levels remained at around 200 mg/dL. She was not obese (the body mass index before pregnancy was 21.9 kg/m2) and had no other medical history. There was no family history of dyslipidemia, pancreatitis, or consanguineous marriages. Careful reviews of her medical record revealed that “milky plasma” was noted at a blood test of the 1st -trimester pregnancy checkup. However, plasma TG levels were not measured, and she missed the opportunity to receive treatment until the episode of acute pancreatitis.

After hospitalization, standard treatments for pancreatitis were initiated, including parenteral nutrition. After the alleviation of HTG and pancreatitis, oral fat intake was resumed stepwise up to 4 g per day while her TG levels were maintained at around 1,000 mg/dL. The detailed method to instruct the patient with a strict low-fat diet (< 4 g of fat, 1600 kcal per day) was described in Supplementary Methods. At 39 weeks of gestation, the patient gave birth safely by cesarean section without complications (Figure 1A). After the delivery, less strict dietary fat restriction (< 24∼30 g per day) was able to control plasma TG levels. After cessation of breastfeeding, EPA and pemafibrate were initiated, and serum TG levels further decreased to around 100 mg/dL. Pemafibrate was discontinued as the patient wanted to conceive again (Figure 1B). Initiation of pemafibrate reduced the plasma TG levels from 403 mg/dL to 126 mg/dL, and its discontinuation increased the plasma TG levels to around 300 mg/dL.

We analyzed the size of plasma lipoproteins by gel-performance liquid chromatography (GP-HPLC) (LipoSEARCH®, Skylight Biotech, Inc., Akita, Japan).6 As shown in Supplementary Fig. 1, severe HTG during pregnancy was associated with the accumulation of large-sized TG-rich lipoproteins (TGRLs). After delivery and the cessation of breastfeeding, large-size fractions of TGRLs were preferentially decreased.

The serum levels of apolipoprotein C-II and A-V were not reduced (23.5 mg/dL and 152.2 µg/L, respectively). The plasma LPL mass, LPL activity, and hepatic lipase (HL) activity were measured using post-heparin plasma obtained after the iv injection of heparin (30 U/kg) (LPL/HTGL Activity Assay Kit®, HTGL Assay Kit®, IBL, Inc.)7 at two different time points: in the presence of pemafibrate (8 months after delivery; TG 146 mg/dL) or in the absence of pemafibrate (11 months after delivery; TG 191 mg/dL). The plasma LPL mass, LPL activity, and HL activity were not abolished but severely decreased compared to healthy control. The presence of pemafibrate (0.2 mg/day) is associated with decreased levels of plasma TG, accompanied by increased levels of LPL mass and activity (Figure 2).

Genomic DNA was extracted from peripheral blood by NucleoSpin Blood L (MAHEREY-NAGEL Lot#1507002), and the whole-exome sequencing was performed using kits according to the manufacturer's instructions (SureSelect Human All Exon V6; illumina HiSeq 2500 (San Diego, California)). Sequences were aligned to the human reference genome (NCBI37/hg19) using the Burrows-Wheeler Aligner. Variant calling was performed using SAMtools. After annotation using data from RefSeq, the 1000 Genomes Project, and dBSNP135, all of the non-synonymous, nonsense, insertion/deletion, or canonical splice site variant calls of the HTG-causing genes were collected. We identified a novel homozygous variant of LMF1 (c.697C>T, p.Arg233Ter, rs199953320) in exon 5, while no other rare variants were identified in other HTG-causing genes (LPL, APOA5, APOC2, and GPIHBP1). The nonsense variant of LMF1 (p.Arg233Ter) was confirmed by Sanger sequencing using the following primers (forward: 5’- GTTGTAAAACGACGGCCACTCTTCGTGGATGGTTCGTCTT-3’, reverse:5’- CACAGGAAACAGCTATGACCAGAGCAAACCAGCTGCACTC-3’; Greiner Bio-One Co., Japan) (Figure 3).