Brain fluid mystery: new study aims to spot hidden dysfunction

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: For LHIPFOLD patients: * Suspicion of diagnosis or diagnosis of LHIPFOLD syndrome documented in the medical record, i.e. presence of these three manifestations: severe intrathecal deficiency in 5MTHF\< 10 nmol/L, hyperproteinorachia \> 1 g/L, and white matter abnormalities on cerebral MRI. * Patient covered by Social Security or Complementary Health Insurance or any equivalent scheme (including AME). For Neurological Controls (NC) : * No chronic pathology (notably no renal, cardiac, pulmonary or hepatic disease) * Patients with one of the following neurological pathologies (confirmed diagnosis or strong suspicion), investigated in the course of routine clinical practice: Alzheimer's disease, multiple sclerosis, amyotrophic lateral sclerosis, intracranial hypertension, normal pressure hydrocephalus, frontotemporal dementia. For Healthy Volunteers (VS): * No chronic pathology (in particular, no renal, cardiac, pulmonary, hepatic or psychiatric disease) * No history of neurological pathology * No chronic alcohol intoxication * No consumption of toxic substances in the week preceding the inclusion visit * No neurological or psychotropic medication. Exclusion Criteria: For all research participants: * Age \<18 * Pregnant and breast-feeding women. * Participant unable to give informed consent. * Participant with a contraindication to MRI: implantable cardiac defibrillators, prostheses, transdermal patches, catheters; implantable pumps; artificial heart valves; implants to treat deafness (if incompatible with MRI); surgical neurostimulator clips., pregnancy, extreme claustrophobia. * Participants with contraindications to contrast injection: known allergy to gadolinium chelates, severe renal insufficiency, pregnancy (BHCG for women of childbearing age prior to MRI), breast-feeding. * Participants with contraindications to LP: haemostasis abnormalities (PT\<50%, platelets \< 40\*109/L), mass syndrome on brain imaging, suspected infection at or near the needle insertion site, coagulopathy, cardiopulmonary insufficiency or respiratory distress. For NC and VS : * Participant under legal protection (guardianship, curatorship) * Participant not covered by Social Security or Complementary Health Insurance or any equivalent scheme (excluding AME). * Taking folate, vitamin C or dietary supplements containing vitamins (excluding vitamin D and E) in the two months prior to inclusion.