Congenital abnormalities of cranial nerve development: overview, molecular mechanisms, and further evidence of heterogeneity and complexity of syndromes with congenital limitation of eye movements.

PURPOSE The clinical and molecular genetic classification of syndromes with congenital limitation of eye movements and evidence of cranial nerve dysgenesis continues to evolve. This monograph details clinical and molecular genetic data on a number of families and isolated patients with congenital fibrosis of the extraocular muscles (CFEOM) and related disorders, and presents an overview of the mechanisms of abnormal patterns of motor and sensory cranial nerve development in these rare syndromes. METHODS Clinical examination of one patient with CFEOM1, one family with clinical features of CFEOM2, one family with recessive CFEOM3, one family with horizontal gaze palsy and progressive scoliosis (HGPPS), and four patients with various combinations of congenital cranial nerve abnormalities. Genotyping of families with CFEOM and HGPPS for polymorphic markers in the regions of the three known CFEOM loci and in the HGPPS region, and mutation analysis of the ARIX and KIF21A genes in patients with CFEOM were performed according to standard published protocols. RESULTS The patient with CFEOM1 had the second most common mutation in KIF21A, a 2861 G>A mutation that resulted in an R954Q substitution. The family with CFEOM2 phenotype did not map to the CFEOM2 locus. The family with recessive CFEOM3 did not map to any of the known loci. The HGPPS family mapped to 11q23-q25. One patient had optic nerve hypoplasia and fifth nerve dysfunction. Two patients had the rare combination of Möbius syndrome and CFEOM. One patient had Möbius syndrome and fifth nerve dysfunction. CONCLUSIONS There is genetic heterogeneity in CFEOM2 and CFEOM3. Abnormalities in sensory nerves can also accompany abnormalities of motor nerves, further substantiating the effect of individual mutations on developing motor as well as sensory cranial nerve nuclei.