Miglustat in Cystic Fibrosis

Inclusion Criteria: * Aged 12 years and older * Male or female Non-pregnant women who are to remain non-pregnant for 3 months after the end of the study. Women of childbearing potential must use a reliable method of contraception. Reliable methods of contraception for female patients include the following: * barrier type devices (e.g., female condom, diaphragm and contraceptive sponge) used ONLY in combination with a spermicide * intrauterine devices * oral contraceptive agent * Depo-Provera™ (medroxyprogesterone acetate) * levonorgestrel implants Abstention, the rhythm method or contraception by the partner alone are NOT reliable methods of contraception. A woman is considered to have child-bearing potential unless she meets at least one of the following criteria: * 6 weeks post-surgical bilateral salpingo-oophorectomy or hysterectomy * Premature ovarian failure confirmed by a specialist gynecologist * Age \> 50 years and not treated with any kind of HRT for at least 2 years prior to screening, and with amenorrhea for at least 24 consecutive months prior to screening and a serum FSH level of \> 40 IU/L at screening. * Age \> 55 years and treated with HRT prior to screening with an appropriate medical documentation of spontaneous amenorrhea for at least 24 months. For female patients in the pediatric age range, a reliable method of contraception must be considered, if appropriate. * Male patients accepting for the duration of the study and for 3 months thereafter to use a condom and not to procreate a child (not in case of azoospermia) * Cystic fibrosis patients homozygous for the F508del mutation as confirmed by genetic test * Signed informed consent prior to any study-mandated procedure Exclusion Criteria: * Any condition prohibiting the correct measurement of the NPD such as upper respiratory tract infection * Acute upper respiratory tract or pulmonary exacerbation requiring antibiotic intervention within 2 weeks of screening * Severe renal impairment (creatinine clearance \< 30 mL/min as per Cockroft and Gault) * Female patients of childbearing potential who will not undergo a pregnancy test prior to enrollment into the study * History of significant lactose intolerance * History of neuropathy * Presence of clinically significant diarrhea (\> 3 liquid stools per day for \> 7 days) without definable cause within 1 month prior to screening * Any known factor or disease that might interfere with treatment compliance, study conduct or interpretation of the results such as drug or alcohol dependence or psychiatric disease * FEV1 \< 25% of predicted normal * Oxygen saturation at rest \< 88% * Active or passive smoking as measured using the Smokelyzer® * Hypersensitivity to miglustat or any excipients * Planned treatment or treatment with another investigationaldrug or therapy (e.g., gene therapy) within 1 month prior to randomization * Breast-feeding, pregnant women or women who plan to become pregnant during the course of the study.