Congenital immobility and stiffness related to biallelic ATAD1 variants

Objective To delineate the phenotype associated with biallelic ATAD1 variants. Methods We describe 2 new patients with ATAD1-related disorder diagnosed by whole-exome sequencing and compare their phenotype to 6 previous patients. Results Patients 1 and 2 had a similar distinctive phenotype comprising congenital stiffness of limbs, absent spontaneous movements, weak sucking, and hypoventilation. Both had absent brainstem evoked auditory responses (BEARs). Patient 1 carried the homozygous p.(His357Argfs*15) variant in ATAD1. In the light of the finding in patient 1, a second reading of exome data for patient 2 revealed the novel homozygous p.(Gly128Val) variant. Conclusions Analysis of the phenotypes of these 2 patients and of the 6 previous cases showed that biallelic ATAD1 mutations are responsible for a unique congenital encephalopathy likely comprising absent BEAR, different from hyperekplexia and other conditions with neonatal hypertonia.