Biallelic UNC80 mutations caused infantile hypotonia with psychomotor retardation and characteristic facies 2 in two Chinese patients with variable phenotypes

Biallelic UNC80 mutations cause infantile hypotonia with psychomotor retardation and characteristic facies 2 (IHPRF2), which is characterized by hypotonia, developmental delay (DD)/intellectual disability (ID), intrauterine growth retardation, postnatal growth retardation and characteristic facial features. We report two unrelated Chinese patients with compound heterozygous UNC80 mutations inherited from their parents, as identified by whole-exome sequencing (WES). Mutations c.3719G>A (p.W1240*)/c.4926_4937del (p.N1643_L1646del) and c.4963C>T (p.R1655C)/c.8385C>G (p.Y2795*) were identified in patient 1 and patient 2, respectively. Although both patients presented with DD/ID and hypotonia, different manifestations also occurred. Patient 1 presented with infantile hypotonia, epilepsy and hyperactivity without growth retardation, whereas patient 2 presented with persistent hypotonia, growth retardation and self-injury without epilepsy. Furthermore, we herein summarize the genotypes and phenotypes of patients with UNC80 mutations reported in the literature, revealing that IHPRF2 is a phenotypically heterogeneous disease. Common facial dysmorphisms include a thin upper lip, a tented upper lip, a triangular face, strabismus and microcephaly. To some extent, the manifestations of IHPRF2 mimic those of Angelman syndrome (AS)-like syndromes.