alfa-fetoproteina

L’alfa-fetoproteina (AFP), è una proteina che viene normalmente prodotta dal sacco vitellino e dal fegato fetale a partire dalla quarta settimana di gravidanza; poiché è in grado di passare dal circolo fetale a quello materno è normale osservare alte concentrazioni sieriche materne di AFP  durante la gravidanza, in particolar modo nel secondo e terzo trimestre di gestazione.

Dopo la nascita, i livelli di AFP cominciano a scendere sensibilmente, sino a raggiungere – nel giro di 12/24 mesi – i valori caratteristici dell’adulto (<6 ng/mL).

La proteina viene prodotta dal gene AFP situato sul braccio q del cromosoma 4 (4q25). Il gene AFP appartiene ad una famiglia filogeneticamente correlata all’albumina sierica. L’AFP, come l’albumina sierica, mostra affinità di legame relativamente forti per una varietà di ligandi. La differenza più notevole è il forte legame preferenziale degli acidi grassi polinsaturi da parte dell’AFP.

La funzione dell’AFP è sconosciuta, ma studi recenti suggeriscono la possibilità che possa avere proprietà immunoregolatorie e/o possa influenzare la proliferazione e la crescita cellulare.

Concentrazioni sieriche elevate durante la gravidanza vengono considerati suggestivi della possibile presenza di anomalie fetali, soprattutto malformazioni congenite del tubo neurale come la spina bifida e l’anencefalia., l’idranencefalia, l’idrocefalia, la cisti di Dandy-Walker, la malformazione di Arnold-Chiari ma anche in caso di onfalocele e gastroschisi.

Al di fuori della gravidanza negli adulti può essere prodotta in maniera anomala in presenza di specifici tumori, primo fra tutti epatocarcinoma ed anche in caso di cirrosi epatica.

A causa dell’associazione del duplice ruolo regolatore nel cancro e delle attività fetali come potenziatore della crescita o inibitore, l’AFP è stata classificata come una proteina “oncofetale”.

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