Loss-of-Function CARS1 Variants in a Patient With Microcephaly, Developmental Delay, and a Brittle Hair Phenotype

Abstract

Background: Mutations in cysteinyl-tRNA synthetase (CARS1) have been implicated in a multisystem disease including microcephaly, developmental delay, and brittle hair and nail phenotypes.

Methods: Here, we present a patient with hepatopathy, hypothyroidism, short stature, developmental delay, microcephaly, muscular hypotonia, brittle hair, and ataxia. The patient underwent exome sequencing to identify potentially pathogenic genetic variants. In addition, identified variants were assessed using yeast complementation assays to determine functional consequences.

Results: Exome sequencing determined that the patient is compound heterozygous for p.Arg341His and p.Arg370Trp CARS1. Yeast complementation assays showed that the p.Arg341His variant has a hypomorphic effect and that the p.Arg370Trp variant causes a complete loss-of-function effect.

Conclusion: This study is the second report of pathogenic CARS1 variants and expands the allelic and phenotypic heterogeneity of CARS1-associated disease.

FIGURE 1

CARS1 variants found in proband. (A) Pedigree showing inheritance of the CARS1 alleles. Squares represent males, circles represent females, and the filled square indicates the affected individual. The arrow indicates the proband. Genotypes are below each individual and question marks indicate unknown genotypes. (B) Photograph showing brittle hair phenotype of the proband. (C) Multiple‐species alignment of CARS1 amino‐acid sequences. The protein annotation of the variant is above, the species names are on the left, and the affected residues are highlighted in red. (D) Sanger sequencing of proband gDNA validating the missense variants found by WES. (E) Diagram of CARS1 protein domains with previously described variants shown at the top of the figure and the newly described variant shown at the bottom of the figure. Variants identified in the proband are in red.

FIGURE 2

CARS1 variants cause a loss‐of‐function effect in yeast complementation assays. (A) Representative yeast complementation data from three separate transformations showing yeast transformed with the pYY1 yeast expression construct containing either no insert, wild‐type CARS1, p.Arg341His CARS1, or one of two independently generated p.Arg370Trp CARS1 constructs. Yeast cells were plated on 5‐FOA and images show undiluted spots from each transformation. (B) Quantification of all replicates (one‐way ANOVA p < 0.0001) demonstrates decreased growth with the p.Arg341His variant (Tukey HSD between wild‐type and p.Arg341His; **** = p _adj < 0.0001) and the p.Arg370Trp variant (Tukey HSD between wild‐type and each independent p.Arg370Trp construct; **** = p _adj < 0.0001).