Aminoacylase 1 (ACY1D) deficiency (MIM 609924) is a rare hereditary metabolic disorder and is characterized by increased excretion of N-acetylated amino acids in urine (serine, glutamic acid, alanine, methionine, glycine, leucine and valine). Malfunction is inherited as an autosomal recessive trait, gene ACY1 (104620.0001) is localized in the 3p21.2. The disease was first described in 2005 by Van Coster.So far it has been About 20 patients are detected in the world. Enzyme Expressed as aminoacylase 1 (EC 3.5.1.14) In the human body, most of all in the kidneys and in the brain. It is homodimeric zinc binding metalloenzyme, which is localized in the cytosol. Catalyzes the hydrolysis (deacetylation) of N-acetylated amino acids to L-amino acids and acetylated group. The phenotype of probands is variable. Disease is most often manifested by neurological and psychiatric disability, psychomotor retardation, muscle disorder tone, more often muscle hypotonia and weakness, convulsions, retardation of the expressive component of speech, growth retardation, sensorineural deafness, tics, hyperactivity and autism disorders Spectrum. Delayed myelination and demyelinating changes in white mass, atrophy of the brain and cerebellum. Probands They can be stigmatized in the face, most often is hypertelorism and a broad root Nose. In our work we describe the first Czech a pediatric patient with aminoacylase deficiency 1.