Missense mutation in the ATPase, aminophospholipid transporter protein ATP8A2 is associated with cerebellar atrophy and quadrupedal locomotion

Abstract

Cerebellar ataxia, mental retardation and dysequilibrium syndrome is a rare and heterogeneous condition. We investigated a consanguineous family from Turkey with four affected individuals exhibiting the condition. Homozygosity mapping revealed that several shared homozygous regions, including chromosome 13q12. Targeted next-generation sequencing of an affected individual followed by segregation analysis, population screening and prediction approaches revealed a novel missense variant, p.I376M, in ATP8A2. The mutation lies in a highly conserved C-terminal transmembrane region of E1 E2 ATPase domain. The ATP8A2 gene is mainly expressed in brain and development, in particular cerebellum. Interestingly, an unrelated individual has been identified, in whom mental retardation and severe hypotonia is associated with a de novo t(10;13) balanced translocation resulting with the disruption of ATP8A2. These findings suggest that ATP8A2 is involved in the development of the cerebro-cerebellar structures required for posture and gait in humans.

Figure 1

Pedigree of Family C with haplotype structure of the disease interval on chromosome 13q12. Haplotype segregating with the disease is boxed. ATP8A2 c.1128 C>G mutation is bold. Please note that the DNA of one affected individual is not available for the study.

Figure 2

Graphical representation of the predicted functional and structural elements of ATP8A2 protein. (a) ATP8A2 is composed of an E1 E2 ATPase domain and a haloacid dehalogenase-like hydrolase (HAD) domain. Ten transmembrane domains were predicted by TMPRED. The mutation lies in the transmembrane region of C-terminal end of E1 E2 ATPase domain (dot). (b) Multiple amino acid sequence alignments show the sequence homology of ATP8A2 protein in vertebrates. I376 residue is indicated with a box. (c) Graphical representation of secondary structural elements as predicted by PSIPRED. The predicted elements (Pred) are indicated above the amino acid (AA) sequences (straight lines: coils; cylinders: helices; arrows: strands). The mutation is predicted to alter the secondary structure of the protein. Transmembrane region is represented within the Pred graphs of wild-type (WT) and mutant (Mut) proteins. EC, extracellular; IC, intracellular.

Figure 3

Expression pattern of ATP8A2 in nine different regions of human brain. Real-time RT-PCR analysis showed that ATP8A2 is expressed in all regions of the brain with the highest levels in the cerebellum.