ReactNative extended button props undefined

I try extend a Button component with a signature attribute to store specific data and add Button specific parameter to fetch. Why event.currentTarget.props is undefined?

import React from 'react';import {  Alert,  Button,  ButtonProps,  GestureResponderEvent,  StyleSheet,  View,} from 'react-native';interface MyButtonProps extends ButtonProps {  signature: string;}class MyButton extends React.Component<MyButtonProps, {}> {  render() {    return <Button {...this.props} />;  }}const App = () => {  const _onPressButton = (event: GestureResponderEvent) => {    Alert.alert(JSON.stringify(event.currentTarget.props));    //let params: string = (event.target as MyButton).props.signature;    //fetch(`http://12.18.1.11/switch?${params}`);  };  return (<View style={styles.container}><View style={styles.buttonContainer}><MyButton          signature="binary=000011110000011&protocol=1&pulselength=133"          onPress={_onPressButton}          title="LED1 (ON)"        /></View><View style={styles.buttonContainer}><MyButton          signature="binary=000111110&protocol=1&pulselength=133"          onPress={_onPressButton}          title="LED1 (OFF)"        /></View></View>  );};const styles = StyleSheet.create({  container: {    flex: 1,    justifyContent: 'center',  },  buttonContainer: {    margin: 20,  },});export default App;

Maybe I not understand well the extension mechanism? Please help me.