Congenital fibrosis of the extraocular muscles (CFEOM) syndrome associated with progressive cerebellar ataxia

A cell type-aware framework for nominating non-coding variants in Mendelian regulatory disorders

Unsolved Mendelian cases often lack obvious pathogenic coding variants, suggesting potential non-coding etiologies. Here, we present a single cell multi-omic framework integrating embryonic mouse chromatin accessibility, histone modification, and gene expression assays to discover cranial motor neuron (cMN) cis-regulatory elements and subsequently nominate candidate non-coding variants in the congenital cranial dysinnervation disorders (CCDDs), a set of Mendelian disorders altering cMN development. We generate single cell epigenomic profiles for ~86,000 cMNs and related cell types, identifying ~250,000 accessible regulatory elements with cognate gene predictions for ~145,000 putative enhancers. We evaluate enhancer activity for 59 elements using an in vivo transgenic assay and validate 44 (75%), demonstrating that single cell accessibility can be a strong predictor of enhancer activity. Applying our cMN atlas to 899 whole genome sequences from 270 genetically unsolved CCDD pedigrees, we achieve significant reduction in our variant search space and nominate candidate variants predicted to regulate known CCDD disease genes MAFB, PHOX2A, CHN1, and EBF3 - as well as candidates in recurrently mutated enhancers through peak- and gene-centric allelic aggregation. This work delivers non-coding variant discoveries of relevance to CCDDs and a generalizable framework for nominating non-coding variants of potentially high functional impact in other Mendelian disorders.

A cell type-aware framework for nominating non-coding variants in Mendelian regulatory disorders

Unsolved Mendelian cases often lack obvious pathogenic coding variants, suggesting potential non-coding etiologies. Here, we present a single cell multi-omic framework integrating embryonic mouse chromatin accessibility, histone modification, and gene expression assays to discover cranial motor neuron (cMN) cis-regulatory elements and subsequently nominate candidate non-coding variants in the congenital cranial dysinnervation disorders (CCDDs), a set of Mendelian disorders altering cMN development. We generated single cell epigenomic profiles for ~86,000 cMNs and related cell types, identifying ~250,000 accessible regulatory elements with cognate gene predictions for ~145,000 putative enhancers. Seventy-five percent of elements (44 of 59) validated in an in vivo transgenic reporter assay, demonstrating that single cell accessibility is a strong predictor of enhancer activity. Applying our cMN atlas to 899 whole genome sequences from 270 genetically unsolved CCDD pedigrees, we achieved significant reduction in our variant search space and nominated candidate variants predicted to regulate known CCDD disease genes MAFB, PHOX2A, CHN1, and EBF3 - as well as new candidates in recurrently mutated enhancers through peak- and gene-centric allelic aggregation. This work provides novel non-coding variant discoveries of relevance to CCDDs and a generalizable framework for nominating non-coding variants of potentially high functional impact in other Mendelian disorders.

5q12.1 deletion: delineation of a phenotype including mental retardation and ocular defects

Array-CGH enables the detection of submicroscopic chromosomal deletions and duplications and leads to an accurate delineation of the imbalances, raising the possibility of genotype to phenotype and mapping minimal critical regions associated with particular patterns of clinical features. We report here on four patients sharing common clinical features (psychomotor retardation, coarse facies and ocular anomalies), with proximal 5q deletions identified by oligo array-CGH. The deletions range from 5.75 to 17.26-Mb in size and occurred de novo. A common 2.63-Mb region between the deletions described here can be defined in 5q12.1 (59,390,122-62,021,754 bp from 5pter, hg18) and includes 12 genes. Among them, KIF2A, which encodes a kinesin superfamily protein, is a particularly interesting candidate for the phenotype, as it suppresses the growth of axonal collateral branches and is involved in normal brain development. Ocular defects, albeit unspecific, seem to be common in the 5q12.1 deletion. Identification of additional cases of deletions involving the 5q12.1 region will allow more accurate genotype-phenotype correlations.

KIF21A variant R954W in familial or sporadic cases of CFEOM1

PURPOSE

To demonstrate the clinical characteristics and determine mutations in the KIF21A gene, encoding a kinesin motor protein in patients with congenital fibrosis of the extraocular muscles (CFEOM) type 1.

METHODS

Patients of five families with congenital fibrosis syndrome and two simplex patients with CFEOM underwent ophthalmologic examination and mutation analysis in the KIF21A gene.

RESULTS

Clinical examination and passive motility testing prior to surgery met criteria for CFEOM. All patients had congenital restrictive ophthalmoplegia primarily affecting muscles innervated by the oculomotor nerve. Complete mutation screening in the KIF21A gene revealed the presence of the known and most common recurrent variant R954W in three families and in two simplex cases. Two families demonstrated linkage to chromosome 16.

CONCLUSIONS

The patients included in the study had marked restriction of movement bilaterally with nearly complete loss of vertical ocular motility, graded reduction of horizontal motility, ptosis, and compensatory chin elevation. The phenotype was variable in patients carrying the same mutation. In one family, all patients were diagnosed with mental retardation, indicating that this syndrome might not only affect the development of cranial nerves, but can also be responsible for general neurologic dysfunction. The screening data suggest frequent and exclusive appearance of the R454W variant in sporadic and familial cases of CFEOM1 in Germany.