To gain a better understanding of the underlying dysmotility in constipation in children, we will use a novel minimal invasive method called 3D Transit. We will examine four groups of children aged 7 to 17 years: healthy children, chronically constipated children (ROM IV criteria), children with neurofibromatosis type 1 and finally children receiving chemotherapy (vincristin) for acute lymphoblastic leukemia.

Inclusion Criteria applicable to all participants:

• Children between 7-17 years of age where permission is granted for the participation by habitable parents with custody of the child. In case of joint custody, permission must be obtained from both parents.

Inclusion criteria applicable only to healthy participants:

• Gastrointestinal healthy children without chronic constipation

Inclusion criteria applicable only to constipated participants:

• Chronic constipation defined by Rom IV criteria, which is a diagnostic score for chronic constipation

Inclusion criteria applicable only to children in vincristine treatment:

• Children with cancer in treatment with vincristine

Inclusion criteria applicable only to patients with NF1:

• Diagnosis of NF1 with gastrointestinal symptoms

Exclusion Criteria:

• Children with parents who are unable to understand the given particpant's information
• Children with known dysregulated metabolic disease
• Previously major intra-abdominal surgery
• CNS surgery
• Other treatment-requiring gastrointestinal disorder
• Systemic steroid treatment within the last week
• Children with difficulty swallowing
• Children with known gastrointestinal obstruction or perforation
• Acute infections
• Diagnosed malabsorption including bile acid malabsorption
• Menarche in girls