Low Efficacy of Genetic Tests for the Diagnosis of Primary Lymphedema Prompts Novel Insights into the Underlying Molecular Pathways

Abstract

Lymphedema is a chronic inflammatory disorder caused by ineffective fluid uptake by the lymphatic system, with effects mainly on the lower limbs. Lymphedema is either primary, when caused by genetic mutations, or secondary, when it follows injury, infection, or surgery. In this study, we aim to assess to what extent the current genetic tests detect genetic variants of lymphedema, and to identify the major molecular pathways that underlie this rather unknown disease. We recruited 147 individuals with a clinical diagnosis of primary lymphedema and used established genetic tests on their blood or saliva specimens. Only 11 of these were positive, while other probands were either negative (63) or inconclusive (73). The low efficacy of such tests calls for greater insight into the underlying mechanisms to increase accuracy. For this purpose, we built a molecular pathways diagram based on a literature analysis (OMIM, Kegg, PubMed, Scopus) of candidate and diagnostic genes. The PI3K/AKT and the RAS/MAPK pathways emerged as primary candidates responsible for lymphedema diagnosis, while the Rho/ROCK pathway appeared less critical. The results of this study suggest the most important pathways involved in the pathogenesis of lymphedema, and outline the most promising diagnostic and candidate genes to diagnose this disease.

Keywords: PI3K/AKT; RAS/MAPK; Rho/ROCK; candidate genes; diagnostic genes; genetic screening; lymphedema; molecular pathways.

Figure 1

Results of genetic tests (n = 147). The pie reports the percentage of negative, inconclusive, and positive test on the whole population considered.

Figure 2

Molecular pathways involved in primary lymphedema. The 28 proteins coded by the genes related to primary lymphedema are placed along known molecular pathways in a somatic cell: RAS/MAPK (violet), PI3K/AKT (lilac), VEGF-C/VEGFR-3 (blue), and HGF/MET (red). The transcription factors are marked in orange, and the light blue proteins are those whose outcome is known, i.e., altered lymphatic valve formation, but the molecular pathway is uncertain. Proteins not encoded by either diagnostic or candidate genes are marked in grey. Proteins encoded by candidate genes are reported in italic. When circled, the protein is a membrane protein. Black arrows represent a positive interaction, while red T-bars represent an inhibition.

Figure 3

The PI3K/AKT pathway in candidate genes for primary lymphedema. Proteins that participate in one of the previously reported molecular pathways are colored: RAS/MAPK (violet), PI3K/AKT (lilac), VEGF-C/VEGFR-3 (blue), and HGF/MET (red). The transcription factors are marked in orange. Proteins that do not participate in any of the previously reported pathways are marked in black. Proteins not encoded by either diagnostic or candidate genes are marked in grey. Proteins encoded by candidate genes are reported in italic. When circled, the protein is a membrane protein. Black arrows represent a positive interaction, while red T-bars represent an inhibition.

Figure 4

The RAS/MAPK pathway in candidate genes for primary lymphedema. Proteins that participate in one of the previously reported molecular pathway are colored: RAS/MAPK (violet), VEGF-C/VEGFR-3 (blue), and HGF/MET (red). The transcription factors are marked in orange. Proteins that do not participate in any of the previously reported pathways are marked in black. Proteins not encoded by either diagnostic or candidate genes are marked in grey. Proteins encoded by candidate genes are reported in italic. When circled, the protein is a membrane protein. Black arrows represent a positive interaction, while red T-bars represent an inhibition.

Figure 5

The Rho/ROCK pathway in candidate genes for primary lymphedema. Proteins that participate in PI3K/AKT molecular pathway are colored in lilac. The transcription factors are marked in orange. Proteins that do not participate in any of the previously reported pathways are marked in black. Proteins not encoded by either diagnostic or candidate genes are marked in grey. Proteins encoded by candidate genes are reported in italic. When circled, the protein is a membrane protein. Black arrows represent a positive interaction, while red T-bars represent an inhibition.

Figure 6

Secondary pathways in candidate genes for primary lymphedema. Proteins that participate in one of the previously reported molecular pathway are colored: RAS/MAPK (violet), PI3K/AKT (lilac). The transcription factors are marked in orange, and the light blue proteins are those whose outcome is known, i.e., altered lymphatic valve formation, but the molecular pathway is uncertain. Proteins that do not participate in any of the previously reported pathways are marked in black. Proteins not encoded by either diagnostic or candidate genes are marked in grey. Proteins encoded by candidate genes are reported in italic. When circled, the protein is a membrane protein. Black arrows represent a positive interaction, while red T-bars represent an inhibition.