Portugal has the highest prevalence of transthyretin familial amyloid polyneuropathy (TTR-FAP) to date, although the number of new cases is decreasing, data from a national epidemiological study shows.
Cases of late-onset disease are also increasing, with more patients developing their first symptoms at the age of 50 or older.
The study, “Epidemiology of Transthyretin Familial Amyloid Polyneuropathy in Portugal: A Nationwide Study,” was published in the journal Neuroepidemiology.
TTR-FAP, a rare progressive and neurodegenerative disease, was first described in 1952 by Corino de Andrade in Portugal. Besides Portugal, the disease is also predominant in Sweden and Japan, a phenomenon known as endemic disease.
To contribute to better healthcare planning for patients in Portugal, researchers conducted a study to estimate the incidence, or rate of new cases, and prevalence, the number of existing cases, of TTR-FAP and assessed the patients’ demographic characteristics.
They performed a national identification of adults with TTR-FAP by registering the number of new patients with prospective follow-up at two national reference centers, one in the city of Porto and another in Lisbon.
They also performed a retrospective estimate of cases by reviewing the reference centers’ registries and medical electronic prescription databases, focusing on the period between 2010 and 2016.
Over these six years, 500 new cases were diagnosed in the TTR-FAP reference centers. The annual incidence rates varied from 0.97 cases per 100,000 adults in 2010 to 0.66 per 100,000 in 2016.
On average, between 2010-2016, 71 new TTR-FAP patients were diagnosed annually, corresponding to 0.87 per 100,000 adults.
“Overall, the number of yearly new TTR-FAP patients has decreased by 31% between 2010 and 2016,” the researchers wrote.
The mean age at disease onset was 42 years old, and 56% of the patients were males.
In more recent years, there has been a higher proportion of late-onset cases, i.e., with a disease onset later than the age of 50. No significant differences were found between genders throughout the years.
In Portugal, the disease prevalence in 2016 was estimated at 22.93 per 100,000 adults, the highest country estimate reported to date. This corresponds to a population of 1,865 individuals with TTR-FAP in Portugal, at a mean age of 52, 46% of whom are men.
Men affected by the disease were significantly younger than women — age 50 versus 54 — but the highest prevalence was among patients between 35 and 44 years old.
These results show that the number of new TTR-FAP cases is decreasing, and the higher number of late-onset cases suggest an “increased disease awareness and improvement in the health care services, including availability of a new treatment,” according to the researchers.
Since the disease is more likely to involve the heart and the kidneys in late-onset patients, leading to an increased burden of the disease, their management poses a challenge to national healthcare services.
“Our findings reinforce the relevance of TTR-FAP epidemiologic surveillance from a public health and policy perspective,” the study concluded.