2024-01-15 10:27:08
Transmissible spongiform encephalopathies (TSE) in humans represent approximately 1 to 2 cases/million person-years in Europe, the most common form (85% of cases) being sporadic Creutzfeldt-Jakob disease (sCJD). Individual susceptibility to developing the disease is notably genetic: codon 129, which codes for a valine (V) or a methionine (M), leads to heterozygosity (MV) or to homozygosity (MM or VV) which is known as being a susceptibility factor for developing the disease in the Caucasian population.
Given the importance of the public health risks induced by these pathologies and the intra- and inter-species transmissibility of prions, surveillance of cases is very important: surveillance networks were initiated in many countries in the 1990s. In France, the national network set up since 1992 is part of the European CJD surveillance network (EuroCJD). It was interesting to learn from the network’s figures over the first 25 years of its establishment.
Analysis of probable or certain cases
The National Surveillance Network for Creutzfeldt-Jakob Diseases and Related Diseases (RNS-CJD) lists all cases notified to it by biochemistry and neuropathology laboratories and by doctors, by contacting the network’s expert neurologists. . All demographic, family and genetic, clinical, biological and imaging data are collected by the network and all registered cases are investigated until diagnosis is confirmed. A case is considered suspicious when an individual presents with a progressive neurological syndrome with at least one clinical sign included in the definitions of CJD. Cases are classified by etiology.
MM homozygosity, the main susceptibility factor
In total, 25,676 suspected cases of prion disease were notified to the French surveillance network between 1992 and 2016, of which 11% (n = 2,907) were considered probable or certain cases. The majority were sporadic cases (86%), occurring at a median age of 69 years. The genetic and infectious forms numbered 240 and 157 (8% and 5% respectively). Among the latter, Creutzfeldt-Jakob disease linked to growth hormone affected 116 subjects with a median age of 27 years, including 115 before 2009.
The numbers of suspected cases and confirmed or probable cases have increased over time: before 2000, they were annually less than 1,500 and around a hundred respectively. Since then, suspected cases number 1,500-2,000 annually, and the number of confirmed or probable cases is between 120 and 140 over 2012-2016. These developments are linked to the increase in sporadic cases.
Among the latter, genetic analysis carried out on 1,704 cases confirmed that a majority (79%) presented homozygosity of codon 129 of the prion protein gene (PRNP). Age of onset was not significantly different depending on codon 129 genotype but some seemed associated with shorter disease duration (MM phenotype). Finally, regarding the temporal distribution of events, it appears that all cases were MM or VV phenotypes between 1992 and 1995.
Vigilance around emerging risks
The authors emphasize that the strong variations in the annual number of sporadic cases and mortality associated with CJD are not unusual, but the recent increase in mortality in France as in other countries may raise questions. The evolution of diagnostic criteria might have increased the detection of cases, but it is difficult to exclude a real simultaneous increase in cases of CJD, for causes which are currently unidentified.
The last case of vCJD occurred in 2014, but two cases potentially of non-food origin were observed in 2020 and 2021: the professional origin is favored (retired research technician and laboratory assistant having worked on BSE respectively 7 and 15 years before symptom onset, both homozygous MM).
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