Expanding the phenotypic spectrum of mutations in LRP2: a novel candidate gene of non-syndromic familial comitant strabismus

Background

Comitant strabismus (CS) is a heterogeneous disorder that is a major contributing factor to unilateral childhood-onset visual impairment. Studies have confirmed that genetic factors play an important role in the development of CS. The aim of this study was to identify the genetic cause of non-syndromic familial CS.

Methods

Fourteen unrelated CS families were recruited for the study. Twelve affected and 2 unaffected individuals from a large four-generation family (CS08) were selected to perform whole genome-wide linkage analysis. Parallel whole-exome sequencing (WES) was conducted in the same family (9 patients and 1 unaffected member) and 31 additional CS cases from 13 other unrelated families. Sanger sequencing was used to determine whether any of the remaining variants co-segregated with the disease phenotype in the corresponding family.

Results

Based on linkage analysis, CS in family CS08 mapped to a novel region of 34.17 centimorgan (cM) on chromosome 2q22.3-2q32.1 between markers D2S151 and D2S364, with a maximum log odds (LOD) score of 3.54 (theta = 0) at D2S142. Parallel WES identified a heterozygous variant, LRP2 c.335 A > G (p.Q112R), located in such a linkage interval that completely co-segregated with the disease in the family. Furthermore, another novel heterozygous variant (c.7274A > G, p.D2425G) in LRP2 that co-segregated was detected in 2 additional affected individuals from another unrelated family by WES. Both variants are predicted to be damaging by PolyPhen-2, SIFT and MutationTaster, and were absent in 100 ethnically matched normal controls.

Conclusion

LRP2 is a novel candidate genetic cause of non-syndromic familial CS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03155-z.

MGST2 and WNT2 are candidate genes for comitant strabismus susceptibility in Japanese patients

Background/Aim

Strabismus is a common condition with misalignment between two eyes that may lead to decrease of visual acuity, lack of binocularity, and diplopia. It is caused by heterogeneous environmental and genetic risk factors. Our previous research has identified new chromosomal susceptibility loci in 4q28.3 and 7q31.2 regions for comitant strabismus in Japanese families. We conducted a verification study by linkage analysis to narrow the chromosomal loci down to a single gene.

Methods

From Japanese and U.S. databases, 24 rsSNPs and 233 rsSNPs were chosen from the 4q28.3 and 7q31.2 region, respectively, and were typed in 108 affected subjects and 96 unaffected subjects of 58 families with primary and non-syndromic comitant strabismus. Three major analytical methods were used: transmission disequilibrium test (TDT), TDT allowing for errors (TDTae), and linkage analysis under dominant and recessive inheritance.

Results

The SNPs with significant P values in TDT and TDTae were located solely at the gene, microsomal glutathione S-transferase 2 (MGST2), on chromosome 4q28.3 locus. In contrast, significant SNPs were dispersed in a few genes, containing wingless-type MMTV integration site family member 2 (WNT2), on chromosome 7q31.2 locus. The distribution of significant SNPs on the 7q31.2 locus showed that only the ST7 to WNT2 region in the same big haplotype block contained significant SNPs for all three methods of linkage analysis.

Conclusions

This study suggests that MGST2 and WNT2 are potential candidates for comitant strabismus in Japanese population.

Comitant strabismus: Perspectives, present and future

Comitant strabismus is a common condition affecting infants, children and adults. Its impact on the affected patient may be severe resulting in visual loss, lack of binocularity, diplopia, social stigma and multiple corrective surgeries within the affected individual's lifespan. It is therefore important that this prevalent disorder should be better understood. We review the current understanding of the demographics and what is known of the etiology, risk factors and genetics of strabismus. We stress the importance of careful clinical assessment in classifying strabismus, and the common pitfalls in the measurement and pre-operative sensory work-up of the strabismic patient. The fact strabismus is comitant does not indicate it is benign: acute onset of comitant esotropia may be a presenting sign of pontine or cerebellar tumor. Lastly, we review the impact of genetics on our understanding of strabismus. While the causes of many types of congenital incomitant strabismus have been elucidated through careful observation and genetic screening, the genetics of comitant strabismus are more complex and multifactorial. Only through careful study and recruitment of large groups of affected individuals and families can we start to answer the question: why is this group of patients pre-disposed to develop strabismus. Doing so will help identify patients at risk, to spare them from the significant morbidity associated with this common disorder.