Presence of Anti-RACH Antibodies and Neurocognitive Disorder in Myasthenic or Alzheimers's Patients.

• Adults with Alzheimer's disease (Procedure): Each patient will undergo a blood draw for the analysis of RACH antibodies in serum. Also an aliquot of frozen spinal fluid of patient kept in biobank ( spinal fluid taken during a puncture as part of routine care) will be used for the analysis of RACH antibodies.
• Adults with Myasthenia (Procedure): Each patient will undergo a blood draw for the analysis of RACH antibodies in serum. Also an aliquot of frozen spinal fluid of patient kept in biobank ( spinal fluid taken during a puncture as part of routine care) will be used for the analysis of RACH antibodies.
• Healhty controls (Other): Frozen spinal fluid of 10 healthy controlled stored in a biobank in Munster, Germanywill be compared to the ones of Adults with Myasthenia and Adults with Alzheimer's disease

Primary outcomes

• The ratio of the number of myasthenic patients with NS-NCD that may be related to myasthenia-related central nervous system damage to the total number of myasthenic patients with CND from all causes combined. [at day 0]

Secondary outcomes

• Measurement of RACH antibodies in serum [at day 0]: dosage by ELISA method of RACH antibodies
• Measurement of RACH antibodies in cerebrospinal liquid [at day 0]: dosage by ELISA method of RACH antibodies

Sex: All, ages: 18 Years to any

Inclusion criteria

For patient with myasthenia :

1. adult person,
2. Diagnosis of anti-AChR positive autoimmune myasthenia gravis, confirmed by clinical and biological data, and categorized in class I to IV according to the Myasthenia Gravis Foundation of America (MGFA) classification,
3. Mild or major neurocognitive disorder (DSM-5 criterion) having benefited from a diagnosis at the CMRR with CSF biomarker dosage and agreement to bio-collect residual CSF,
4. Agreeing to sign the free and informed consent,
5. Affiliate or beneficiary of a social security system.

For patient with Alzheimer Disease :

1. adult person,
2. Mild or major neurocognitive disorder (DSM-5 criterion) having benefited from a diagnosis at the CMRR with CSF biomarker dosage and agreement to bio-collect residual CSF,
3. Neurocognitive disorder only linked to Alzheimer's disease (IWG-2 criterion): typical or atypical clinical form with biomarkers of Alzheimer's disease in the CSF;
4. Agreeing to sign the free and informed consent,
5. Affiliate or beneficiary of a social security system.

For healty control :

1. absence of memory complaint,
2. absence of neurocognitive disorder,
3. Having agreed to carry out analyzes as part of research, on these CSF samples stored in the biobank of the Institute of Translational Neurology in Münster (Germany)

Exclusion Criteria:

For patient with myasthenia :

1. Person who does not have sufficient command of the French language to understand, read and write, to take neuropsychological tests;
2. Need to use the routine complementary CSF tube to carry out additional diagnostic explorations as part of routine care,
3. Vulnerable people are defined in articles L1121-5 to -8 ( Pregnant women, parturients and breastfeeding mothers, persons deprived of their liberty by a judicial or administrative decision, persons hospitalized without consent under articles L. 3212-1 and L. 3213-1 who do not fall under the provisions of article L. 1121-8, and persons admitted to a health or social establishment for purposes other than research/Adults who are subject to a legal protection measure or who are unable to express their consent.),

For patient with Alzheimer Disease :

1\) vulnerable people are defined in articles L1121-5 to -8 ( Pregnant women, parturients and breastfeeding mothers, persons deprived of their liberty by a judicial or administrative decision, persons hospitalized without consent under articles L. 3212-1 and L. 3213-1 who do not fall under the provisions of article L. 1121-8, and persons admitted to a health or social establishment for purposes other than research/Adults who are subject to a legal protection measure or who are unable to express their consent.)

• SACCO GUILLAUME, MD, Principal investigator, Centre Hospitalier Universitaire de Nice