Neurological Conditions Associated With Aminoacylase 1 Deficiency

An inborn error of metabolism marked by a characteristic pattern of urinary N-acetyl amino acid excretion and neurologic symptoms.

Epidemiology

Prevalence is unknown but less than 20 cases have been reported in the literature so far.

Clinical description

Most individuals with ACY1D identified so far are children who underwent selective screening tests for inborn errors of metabolism prompted mainly by delayed psychomotor development or by the occurrence of seizures. However, there is a considerable phenotypic variability between ACY1D individuals.

Etiology

ACY1D is caused by biallelic mutations in the ACY1 gene (3p21.2). ACY1 catalyzes the formation of free amino acids from N-acetylated precursors. The enzyme is strongly expressed in the human brain and is a potential modifier affecting the severity or manifestation of different neurologic diseases.

Diagnostic methods

Diagnosis is made by gas chromatography-mass spectrometry (GC-MS) analysis of urinary organic acids revealing increased levels of N-acetylated amino acids, including methionine, glutamine, alanine, leucine, glycine, valine, and isoleucine derivatives, or by NMR spectroscopy of urine. The diagnosis can be confirmed by identification of mutations in the ACY1 gene and by detection of reduced ACY1 enzyme activity in Epstein-Barr virus (EBV)-transformed lymphoblasts or in fibroblasts.

Genetic counseling

ACY1D is transmitted as an autosomal recessive trait.

Management and treatment

Management is symptomatic only.

Prognosis

Due to the small number of individuals known to have ACY1D and due to the young age of the reported patients, the clinical course cannot be fully predicted and the prognosis is unknown. Characterization of additional patients and long-term follow-up are indicated.