Congenital mirror movements: mutational analysis of RAD51 and DCC in 26 cases

Abstract

Objective: We screened a large series of individuals with congenital mirror movements (CMM) for mutations in the 2 identified causative genes, DCC and RAD51.

Methods: We studied 6 familial and 20 simplex CMM cases. Each patient had a standardized neurologic assessment. Analysis of DCC and RAD51 coding regions included Sanger sequencing and a quantitative method allowing detection of micro rearrangements. We then compared the frequency of rare variants predicted to be pathogenic by either the PolyPhen-2 or the SIFT algorithm in our population and in the 4,300 controls of European origin on the Exome Variant Server.

Results: We found 3 novel truncating mutations of DCC that segregate with CMM in 4 of the 6 families. Among the 20 simplex cases, we found one exonic deletion of DCC, one DCC mutation leading to a frameshift, 5 missense variants in DCC, and 2 missense variants in RAD51. All 7 missense variants were predicted to be pathogenic by one or both algorithms. Statistical analysis showed that the frequency of variants predicted to be deleterious was significantly different between patients and controls (p < 0.001 for both RAD51 and DCC).

Conclusion: Mutations and variants in DCC and RAD51 are strongly associated with CMM, but additional genes causing CMM remain to be discovered.

Figure 1. Deletion of exons 4 and 5 of DCC in a simplex case

The quantitative multiplex PCR of short fluorescent fragments profiles of the deletion carrier (in red) and of a normal control (in blue) are superimposed. They are normalized using HMBS as a control amplicon. A 2-fold reduction of exons 4 and 5 is observed in the patient's profile. DCC = deleted in colorectal carcinoma; HMBS = hydroxymethylbilane synthase; RAD51 = RAD51 recombinase.

Figure 2. Distribution of all the identified variants and mutations throughout the DCC and RAD51 proteins

(A) DCC. (B) RAD51. AAA+ = ATPase domain; DCC = deleted in colorectal carcinoma; FN3 = fibronectin type III-like domain; HhH = helix-hairpin-helix domain; IgC2 = immunoglobulin-like type C2 domain; P1, P2, P3 = conserved domains of the cytoplasmic region; RAD51 = RAD51 recombinase; TM = transmembrane domain.