Biomarker for Creatine Deficiency Syndromes (BioCDS)

INCLUSION CRITERIA: * Informed consent will be obtained from the patient or the parents before any study related procedures. * Patients of both genders older than 2 months * The patient has a diagnosis of the Creatine Deficiency Syndromes or a high-grade suspicion for the Creatine Deficiency Syndromes High-grade suspicion is present, if one or more inclusion criteria are valid: * Positive family anamnesis for the Creatine Deficiency Syndromes * Intellectual disability * Seizure disorder of variable severity * Developmental delay * Speech/language delay * Movement disorder * Behavioral disorder (autism, hyperactivity, self-injury) * Intractable epilepsy EXCLUSION CRITERIA: * No Informed consent from the patient or the parents before any study related procedures. * Patients of both gender younger than 2 months * No diagnosis of Creatine Deficiency Syndromes or no valid criteria for profound suspicion of the Creatine Deficiency Syndromes