Symfony 2 trouble with Single Table Inheritance - php

Question

I'm new to Symfony and Doctrine and I'm trying to implement a simple user registration system with two types of users, a Client and an Expert.
I have an abstract class Usuario with common data that both users share and the other two which extend from it.
The problem is that when I run the command app/console doctrine:schema:update, it generates the table Usuario with all fields of the Usuario class but only one from the Experto class.
Here is my code:
Class Usuario:
/**
* Usuario
*
* #ORM\Entity
* #ORM\Table(name="Usuario")
* #ORM\InheritanceType("SINGLE_TABLE")
* #ORM\DiscriminatorColumn(name="tipo", type="string")
* #ORM\DiscriminatorMap( {"cliente" = "Cliente", "experto" = "Experto"} )
*/
abstract class Usuario
{
/**
* #var integer
*
* #ORM\Id
* #ORM\Column(name="id", type="integer")
* #ORM\GeneratedValue(strategy="AUTO")
*/
protected $id;
/**
* #var string $nombre
*
* #ORM\Column(name="nombre", type="string", length=255)
*/
protected $nombre;
/**
* #var string $email
*
* #ORM\Column(name="email", type="string", length=255)
*/
protected $email;
/**
* #var string $password
*
* #ORM\Column(name="password", type="string", length=32)
*/
protected $password;
/**
* #var \DateTime $fecha_registro
*
* #ORM\Column(name="fecha_registro", type="datetime")
*/
Setters and Getters
Class Experto:
/**
* Experto
*
* #ORM\Entity(repositoryClass="QuienLoRepara\UsuariosBundle\Entity\ExpertoRepository")
*/
class Experto extends Usuario
{
/**
* #var string $nombre_negocio
*
* #ORM\Column(name="nombre_negocio", type="string", length=255)
*/
protected $nombre_negocio;
/*
* #var text $descrip_negocio
*
* #ORM\Column(name="descrip_negocio", type="text")
*/
protected $descrip_negocio;
/*
* #var string $descripcion
*
* #ORM\Column(name="direccion", type="string", length=255)
*/
protected $direccion;
/*
* #var string $telefono
*
* #ORM\Column(name="telefono", type="string", length=255)
*/
protected $telefono;
/*
* #var string $actividad
*
* #ORM\Column(name="actividad", type="string", length=255)
*/
protected $actividad;
/*
* #var decimal $latitud
*
* #ORM\Column(name="latitud", type="decimal", precision=10, scale=8)
*/
protected $latitud;
/*
* var decimal $longitud
*
* #ORM\Column(name="longitud", type="decimal", precision=11, scale=8)
*/
protected $longitud;
/**
* #var Collection
* #ORM\OneToMany(targetEntity="Skill", mappedBy="experto")
* #ORM\JoinColumn(name="usuario_id", referencedColumnName="id")
*/
protected $skills;
The result is a table called Usuario with all properties of the class usuario and only the property nombre_negocio of the Experto class.
Any ideas what I'm doing wrong?
Thanks in advance.