...
sonata_user:
security_acl: false
manager_type: orm # can be orm or mongodb
profile:
    register:
    form:
        type:                 custom_user_registration
        handler:              sonata.user.registration.form.handler.default
        name:                 sonata_user_registration_form
        validation_groups:
        # Defaults:
        - myRegistration
        - Default
...

ApplicationSonataUserBundleEntityUser:
    constraints:
        - SymfonyBridgeDoctrineValidatorConstraintsUniqueEntity: email
    properties:
        email:
             - NotBlank:
                 groups: [myRegistration]
             - Email:
                groups: [myRegistration]
                checkMX: true
        plainPassword:
             - NotBlank:
                 groups: [myRegistration]
             - Length:
                 groups: [myRegistration]
                 min: 6
                 max: 1024
                 minMessage: "[T]PASWORD_IS_SHORT[/T]"

class RegistrationFormType extends AbstractType {

    public function buildForm(FormBuilderInterface $builder, array $options) {
        $builder->remove('username')
            ->remove('email')
            ->remove('plainPassword');
        $builder
            ->add('email', 'email',  array(
                'label' => '[T]EMAIL[/T]',
                'translation_domain' => 'FOSUserBundle'
            ))
            ->add('plainPassword', 'repeated', array(
                'type' => 'password',
                'options' => array('translation_domain' => 'FOSUserBundle'),
                'first_options' => array('label' => '[T]PASSWORD[/T]'),
                'second_options' => array('label' => '[T]PASSWORD_CONFIRM[/T]'),
                'invalid_message' => 'fos_user.password.mismatch',
            ))
            ->add('us_reportable_agreement', 'choice', array(
                'label_attr' => array('class' => 'centered_label'),
                'label' => '[T]US_REPORTABLE_AGREEMENT[/T]',
                'required' => true,
                'expanded'=>true,
                'multiple'=>false,
                'choices' => array('accept' => '[T]US_REPORTABLE_AGREEMENT_ACCEPT[/T]', 'decline' => '[T]US_REPORTABLE_AGREEMENT_DECLINE[/T]'),
            ));
    }