According to the World Health Organization (WHO), mental retardation (MR) is defined by an intelligence quotient (IQ) < 70 and touches between 1 to 3 % of the general population. Profound mental retardation (QI <25), severe (IQ: 25-40) and moderate (QI : 40-50) have a prevalence of 0,3-0,5% while the prevalence of mild MR, defined by an IQ between 50 and 70 is evaluated to about 1,5 %.

The origin of MR can be infectious, toxic, traumatic, genetic or environmental. genetic causes of MR gather the number and structure anomalies of the chromosomes, the genomic microreorganization, monogenic diseases and more rarely other non Mendelian-inherited anomalies like print or epigenetic anomalies, mutations of the mitochondrial genome etc... Genetic causes represents 50% of moderate to severe, whereas environmental factors (malnutrition, cultural deprivation,...) plays an important role in mild MR.

The main goal of this study is to get an innovative tool (neuronal distinction of iPSC) that wil allow to study the functionnal impact of mutations uppon genes probably involved in MR like MYT1L. The main criteria associated to characterisation of the tool by the trial is the study of the pluripotency of iPSC obtained and to highlight the mutation of the gene MYT1L in the iPSC.

Neurons from the iPSC of the patient and his father du patient wille also be morphologically characterised, but also thanks to the expression of specifically neurals genes.

Characteristics of iPSC and neurons from d'iPSC with MYT1L mutation will be compared among the patient and his father, in relation with the same cells coming from the two witnesses.

Inclusion Criteria :

• Patient with an intellectual deficiency and/or associated signs that received a chromosomic analysis by CGH-array revealing a variant of unknown signification involvingone or more genes candidates for mental retardation.
• Certificate of genetic genetic counselling and signed consent.
• Under 18 persons may be necessary because intellectual deficiency is often diagnosed before the adult age.
• Number of cases is very limited in this preliminary study and only one patient showing a rare mutation of MYT1L gene and his father ( asymptomatic carrier of the same mutation) will be study.
• Affiliation to a social security system

Exclusion Criteria :

• Persons mentionned L1121-5 to L1121-8 of CSP (all protected persons)
• Persons suffering from acute infections for the practice of cutaneous biopsy under local anesthesia.
• Persons showing an hemostasis disorder acquired or induced
• Persons sous traitement antiagrégant anticoagulant
• Persons with a mutation in th gene MYT1L