Dunnigan lipodystrophy syndrome: French National Diagnosis and Care Protocol (PNDS; Protocole National de Diagnostic et de Soins)

Dunnigan syndrome, or Familial Partial Lipodystrophy type 2 (FPLD2; ORPHA 2348), is a rare autosomal dominant disorder due to pathogenic variants of the LMNA gene. The objective of the French National Diagnosis and Care Protocol (PNDS; Protocole National de Diagnostic et de Soins), is to provide health professionals with a guide to optimal management and care of patients with FPLD2, based on a critical literature review and multidisciplinary expert consensus. The PNDS, written by members of the French National Reference Center for Rare Diseases of Insulin Secretion and Insulin Sensitivity (PRISIS), is available on the French Health Authority website (in French). Dunnigan syndrome is characterized by a partial atrophy of the subcutaneous adipose tissue and by an insulin resistance syndrome, associated with a risk of metabolic, cardiovascular and muscular complications. Its prevalence, assessed at 1/100.000 in Europe, is probably considerably underestimated. Thorough clinical examination is key to diagnosis. Biochemical testing frequently shows hyperinsulinemia, abnormal glucose tolerance and hypertriglyceridemia. Elevated hepatic transaminases (hepatic steatosis) and creatine phosphokinase, and hyperandrogenism in women, are common. Molecular analysis of the LMNA gene confirms diagnosis and allows for family investigations. Regular screening and multidisciplinary monitoring of the associated complications are necessary. Diabetes frequently develops from puberty onwards. Hypertriglyceridemia may lead to acute pancreatitis. Early atherosclerosis and cardiomyopathy should be monitored. In women, polycystic ovary syndrome is common. Overall, the management of patients with Dunnigan syndrome requires the collaboration of several health care providers. The attending physician, in conjunction with the national care network, will ensure that the patient receives optimal care through regular follow-up and screening. The various elements of this PNDS are described to provide such a support.

[Inflammasome and interleukin 1]

The innate immune system, which corresponds to the first line of defense against microorganisms, brings into play cell surface and intracellular sensors that detect pathogen ligands and danger signals. Among them, NOD-like receptors (NLRs) are intracellular proteins involved in inflammatory signaling pathways. NLRs are part of multiprotein complexes, called inflammasomes, which usually bring into play a NLR, an adaptor protein called ASC, and the pro-inflammatory caspase 1 protein. The activation of inflammasome by different stimuli triggers the proteolytic cleavage of pro-caspase 1 into active caspase 1, which, in turn, converts pro-interleukin 1β (pro-IL1β) into the mature IL1β. IL1β plays a crucial role in systemic inflammation due to its ability to induce the expression of a large panel of pro-inflammatory genes and to act on various target organs. Mutations in NLR genes are responsible for several autoinflammatory and/or autoimmune disorders. For example, mutations in NLRP3, which are responsible for three Mendelian autoinflammatory disorders called cryopyrinopathies, lead to inflammasome autoactivation. Peripheral blood mononuclear cells from patients carrying NLRP3 mutations secrete high levels of IL1β; in many patients presenting with autoinflammatory disorders, blocking IL1 activity by anti-IL1 therapy significantly improves their manifestations. The mechanisms leading to IL1β hypersecretion in other autoinflammatory disorders remain to be identified, as is the case for the role of each inflammasome in vivo. Better knowledge in this field should also contribute to the development of new anti-inflammatory treatments.

PYPAF1 nonsense mutation in a patient with an unusual autoinflammatory syndrome: role of PYPAF1 in inflammation

OBJECTIVE

To gain insight into the pathophysiology of an unusual autoinflammatory syndrome, in a patient of Armenian origin, that mimicked familial Mediterranean fever (FMF) but with episodes triggered by generalized exposure to cold, and to further elucidate the controversial function of the protein encoded by PYPAF1, whose mutations (exclusively missense to date) have been identified in 3 hereditary recurrent fever syndromes.

METHODS

The patient's DNA was screened for mutations in both MEFV, the gene responsible for FMF, and PYPAF1. The ability of different recombinant PYPAF1 isoforms, expressed in HEK 293 cells, to regulate NF-kappaB signaling was subsequently assessed.

RESULTS

No disease-causing mutation was found in MEFV. However, a nonsense mutation (p.Arg554X) was identified in PYPAF1; this defect resulted in a truncated protein lacking all leucine-rich repeats. Study of the wild-type and mutant PYPAF1 recombinant proteins revealed that PYPAF1 inhibited NF-kappaB proinflammatory pathways, and that the identified nonsense mutation impaired this property.

CONCLUSION

These molecular and clinical findings, together with the clinical manifestations in the patient, which call into question the current nosology of the hereditary recurrent fever syndromes, are consistent with the hypothesis that PYPAF1 acts as an inhibitor of NF-kappaB signaling. They also provide a clear elucidation of the functional consequences of this nonsense PYPAF1 mutation not previously described in the literature, which result in a partial loss of function and may thereby explain the pathophysiology of the autoinflammatory syndrome observed in this patient.