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Practitioner's Corner
J Investig Allergol Clin Immunol 2019; Vol. 29(5): 378-398 © 2019 Esmon Publicidad
Thus, the 12-kDa conger allergen we identified proved to be
a ß-parvalbumin.
In terms of gastronomy, conger is one of the 30 main
commercial fish species in Europe. Only 3 cases of mild
conger allergy have previously been reported, and in all 3 the
patients had multiple fish allergies. In addition, the proteins
involved were not identified [3,4]. S formosus is also known
as Malay tongue. It belongs to the order Osteoglossiformes,
which is very distant from the order Anguilliformes. To
our knowledge, it has never been reported to cause allergic
reactions.
ß-Parvalbumins are the main fish allergens and are
recognized by 95% of fish-allergic patients [5]. Although
ß-parvalbumins are considered to be highly cross-reactive,
especially between closely related fish species, isolated clinical
allergy to a single fish species has been described for swordfish,
tuna/marlin, salmon, sole, tilapia, and pangasius/tilapia [6].
We think this ß-parvalbumin probably behaves as a selective
allergen of the Congridae family, because it was not recognized
in the other fish extracts tested, including eel extract, and the
patient tolerated all other fish species (both cooked and raw).
We think that our commonly identified LFLQNFASGAR
sequence does not include relevant IgE-binding epitopes and
that clinically relevant conger parvalbumin epitopes must be
located in different parts of the protein and show no homology
with other parvalbumins, thus explaining the lack of cross-
reactivity between conger allergens and other allergenic
parvalbumins in fish.
Parvalbumins are classified into 2 different families,
namely, α and ß parvalbumins. α-Parvalbumins are present in
birds, amphibians, cartilaginous fish, mammals, and crocodiles.
To date, the only reports of allergy caused by α-parvalbumin
involved one patient with allergy to frog leg and another with
allergy to crocodile and cartilaginous fish [7,11]. In contrast,
ß-parvalbumins are present in bony fish, especially white fish,
and are highly allergenic. They have a single 113–amino acid
chain, with 2 specific calcium-binding sites. ß-parvalbumins
are thermostable proteins with a molecular weight of around
12-14 kDa. In addition, they are resistant to denaturation and
enzymatic digestion, which can cause severe reactions [6].
Fish allergenicity depends on the amount of white muscle and
processing (canned, cooked, raw) [8].
The 40-50–kDa protein recognized by the patient in
the present report is probably enolase or aldolase [9], the
second most frequent fish allergens (albeit with doubtful
clinical relevance), which are recognized by around 50% of
patients. These antigens cannot be responsible for symptoms
with cooked conger, since they are thermolabile proteins.
Furthermore, they have no clinical relevance in the present
case, given that the patient did not have symptoms with
other raw fish species. Less frequent fish allergens that have
been described include collagen, tropomyosin, aldehyde
dehydrogenase, and protamine. In some cases, they seem to
be species-specific.
In summary, we report the first case of anaphylaxis due to
conger allergy. We also describe the first allergen in conger
(ie, a ß-parvalbumin), and a new selective parvalbumin in fish.
Interestingly, conger can also behave as a hidden allergen, since
it is used to add a fish flavor to typical dishes.
Manuscript received January 11, 2019; accepted for publication
May 7, 2019.
Laura Argiz Álvarez
C/ Diego de León, 62
Hospital Universitario La Princesa
Servicio de Alergia
28006 Madrid, Spain
E-mail:
Funding
The authors declare that no funding was received for the
present study.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
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