Case Report: Identification of a Novel Homozygous Mutation in GPD1 Gene of a Chinese Child With Transient Infantile Hypertriglyceridemia

Glycerol 3-phosphate dehydrogenases (1 and 2) in cancer and other diseases

The glycerol 3-phosphate shuttle (GPS) is composed of two different enzymes: cytosolic NAD+-linked glycerol 3-phosphate dehydrogenase 1 (GPD1) and mitochondrial FAD-linked glycerol 3-phosphate dehydrogenase 2 (GPD2). These two enzymes work together to act as an NADH shuttle for mitochondrial bioenergetics and function as an important bridge between glucose and lipid metabolism. Since these genes were discovered in the 1960s, their abnormal expression has been described in various metabolic diseases and tumors. Nevertheless, it took a long time until scientists could investigate the causal relationship of these enzymes in those pathophysiological conditions. To date, numerous studies have explored the involvement and mechanisms of GPD1 and GPD2 in cancer and other diseases, encompassing reports of controversial and non-conventional mechanisms. In this review, we summarize and update current knowledge regarding the functions and effects of GPS to provide an overview of how the enzymes influence disease conditions. The potential and challenges of developing therapeutic strategies targeting these enzymes are also discussed.

GPD1 inhibits the carcinogenesis of breast cancer through increasing PI3K/AKT-mediated lipid metabolism signaling pathway

Glycerol 3-phosphate dehydrogenase 1 (GPD1) acts as a tumor suppressor in various types of cancer. However, the mechanisms of GPD1 anti-tumor remain unclear in breast cancer. This study aims to explore the function and clinical relevance of GPD1 in breast cancer. We confirmed that GPD1 inhibited the ability of proliferation, migration, and invasion in GPD1 overexpression breast cancer cells by CCK-8, wound healing, and Transwell assays, respectively. We found that GPD1 overexpression activated the lipid synthesis pathway and PI3K/AKT signaling pathway. The inhibitory effect of GPD1 on breast cancer cells was also weakened after treatment with LY294002, a PI3K/AKT pathway inhibitor. These results indicated that GPD1 suppressed the carcinogenesis of breast cancer through increasing PI3K/AKT-mediated lipid signaling pathways. Meanwhile, we detected that the relationship between GPD1 level and survival rate presents a positive correlation in breast cancer patients from the Cancer Genome Atlas (TCGA) database. Therefore, GPD1 can be a prognostic biomarker and target in developing therapeutic strategies for breast cancer patients.

Rare Transient Infantile Hypertriglyceridemia with Hypoglycemia and Insulin Resistance Caused by a Novel GPD1 Mutation

Introduction

Transient infantile hypertriglyceridemia (HTGTI) is a rare autosomal recessive disease. At present, only 20 cases of HTGTI have been reported worldwide. Hence, it is necessary to further assess the phenotypic and genetic variation spectra of HTGTI.

Case Presentation

A 10-month-old male infant was diagnosed with hypertriglyceridemia, hepatomegaly, liver injury, fasting hypoglycemia, and insulin resistance. Trio-whole exome sequencing (trio-WES) was performed on the patient and his parents. Bioinformatics software was used to analyze the suspected genes and potential pathogenicity of the resulting mutant proteins. The results of trio-WES demonstrated that the patient was homozygous for a novel mutation in the GPD1 gene (NM_005276.3; c.805C>T/p.Arg269Trp), whereas his parents were heterozygous for the same mutation. Bioinformatics prediction results demonstrated that the mutation might affect the protein function, and crystal simulation results showed that the mutation might affect the protein-binding ability of the enzyme.

Conclusion

Our results indicated that the novel homozygous mutation in GPD1 could be the pathogenic factor in the patient. Our report highlights the value of genome sequencing in the diagnosis of infant liver disease with low phenotypic heterogeneity.

Clinical characteristics and variant analyses of transient infantile hypertriglyceridemia related to GPD1 gene

Objective: Our study aims to summarize and analyze the clinical characteristics of transient infantile hypertriglyceridemia (HTGTI) and variants in the glycerol-3-phosphate dehydrogenase 1 (GPD1) gene and the effect of HTGTI on the protein structure of GPD1.

Methods: Retrospective analysis, using the general data, symptoms, signs, and auxiliary examinations, was performed on patients with HTGTI, which were confirmed by genetic testing in our hospital and reported cases online. The clinical data were analyzed using statistical and bioinformatic approaches.

Results: A total of 31 genetically confirmed HTGTI patients were collected from our hospital and cases reported in the literature. The clinical manifestations showed the median age of onset was 6.0 (1.9, 12.0) months. All the patients had normal psychiatric status, but 22.6% of them presented growth retardation and short stature, 93.5% had hepatomegaly, and 16.1% had splenomegaly. Just a few children were reported with jaundice, cholestasis, and obesity (3.2–6.5%). The laboratory investigations showed that 96.8% of them had hypertriglyceridemia (HTG) with a median level of 3.1 (2.1, 5.5) mmol/L, but only 30.0% had returned to normal during follow-up. In addition, 93.5% of patients had elevated alanine aminotransferase (ALT) with an average level of 92.1 ± 43.5 U/L, while 38.7% had hypercholesterolemia. Upon abdominal imaging, all patients presented fatty liver and liver steatosis, with 66.7% of patients showing hepatic fibrosis. Statistical differences in triglyceride (TG) level were observed in the ≤6 months group compared with the older groups and in the 13 months to 6 years group with >6 years group (H = 22.02, P < 0.05). The restricted cubic spline model showed that severe HTG decreased in the early stage of infants to the normal level; however, it rebounded again to a mild or moderate level after the following days. The genetic test revealed that the main variant types of the GPD1 gene were missense variants (51.6%), followed by splicing variants (35.5%) and nonsense variants (12.9%). Of patients, 87.1% had homozygous variants, with the most frequent loci being c.361-1G > C and c.895G > A.

Conclusion: The common manifestations of HTGTI were HTG, hepatomegaly, elevated liver transaminases, and hepatic steatosis in early infancy. However, the recurrence of aberrant HTG may pose long-term detrimental effects on HTGTI patients.

Transient infantile hypertriglyceridaemia due to homozygous mutation in GPD1 presenting in childhood with hepatic adenoma

Hypertriglyceridaemia in infancy is usually secondary to underlying metabolic disorder which usually has a genetic basis unlike the adult population. One such recently described entity is transient infantile hypertriglyceridaemia (HTGTI). In this disorder, mutation in glycerol-3-phosphate (G3P) dehydrogenase gene leads to deficiency of G3P dehydrogenase resulting in hypertriglyceridaemia and hepatomegaly. Clinical features tend to improve with age but may develop fibrosis. Our patient presented in infancy with hypoglycaemia, hepatomegaly, high transaminases and hypertriglyceridaemia. Limited genetic test for glycogen storage disorder was negative and was kept under follow-up. On follow-up, he developed hepatic lesion and his hepatomegaly with hypertriglyceridaemia persisted. There are only a few cases reported worldwide and none has reported development of adenoma so far. This could be the first report of development of adenoma in transient HTGTI.