We report that eight heterozygous missense mutations in TUBB3, encoding the neuron-specific β-tubulin isotype III, result in a spectrum of human nervous system disorders we now call the TUBB3 syndromes. Each mutation causes the ocular motility disorder CFEOM3, whereas some also result in intellectual and behavioral impairments, facial paralysis, and/or later-onset axonal sensorimotor polyneuropathy. Neuroimaging reveals a spectrum of abnormalities including hypoplasia of oculomotor nerves, and dysgenesis of the corpus callosum, anterior commissure, and corticospinal tracts. A knock-in disease mouse model reveals axon guidance defects without evidence of cortical cell migration abnormalities. We show the disease-associated mutations can impair tubulin heterodimer formation in vitro, although folded mutant heterodimers can still polymerize into microtubules. Modeling each mutation in yeast tubulin demonstrates that all alter dynamic instability whereas a subset disrupts the interaction of microtubules with kinesin motors. These findings demonstrate normal TUBB3 is required for axon guidance and maintenance in mammals.

Congenital fibrosis of the extraocular muscles type 1 (CFEOM1; OMIM #135700) is an autosomal dominant strabismus disorder associated with defects of the oculomotor nerve. We show that individuals with CFEOM1 harbor heterozygous missense mutations in a kinesin motor protein encoded by KIF21A. We identified six different mutations in 44 of 45 probands. The primary mutational hotspots are in the stalk domain, highlighting an important new role for KIF21A and its stalk in the formation of the oculomotor axis.

Gastric adenocarcinoma and proximal polyposis of the stomach (GAPPS) is an autosomal-dominant cancer-predisposition syndrome with a significant risk of gastric, but not colorectal, adenocarcinoma. We mapped the gene to 5q22 and found loss of the wild-type allele on 5q in fundic gland polyps from affected individuals. Whole-exome and -genome sequencing failed to find causal mutations but, through Sanger sequencing, we identified point mutations in APC promoter 1B that co-segregated with disease in all six families. The mutations reduced binding of the YY1 transcription factor and impaired activity of the APC promoter 1B in luciferase assays. Analysis of blood and saliva from carriers showed allelic imbalance of APC, suggesting that these mutations lead to decreased allele-specific expression in vivo. Similar mutations in APC promoter 1B occur in rare families with familial adenomatous polyposis (FAP). Promoter 1A is methylated in GAPPS and sporadic FGPs and in normal stomach, which suggests that 1B transcripts are more important than 1A in gastric mucosa. This might explain why all known GAPPS-affected families carry promoter 1B point mutations but only rare FAP-affected families carry similar mutations, the colonic cells usually being protected by the expression of the 1A isoform. Gastric polyposis and cancer have been previously described in some FAP-affected individuals with large deletions around promoter 1B. Our finding that GAPPS is caused by point mutations in the same promoter suggests that families with mutations affecting the promoter 1B are at risk of gastric adenocarcinoma, regardless of whether or not colorectal polyps are present.

Point mutations and gross deletions of PITX2 appear to produce an equivalent haploinsufficiency phenotype. Quantitative PCR is an efficient means of detecting causative PITX2 deletions in patients with AR and may increase the detection rate at this locus.

We report clinical, cytogenetic, and molecular studies in 65 patients with isolated lissencephaly sequence (ILS). All had type I lissencephaly of varying severity and a grossly normal cerebellum. Some had additional brain abnormalities. Facial appearance was essentially normal. All had severe to profound mental retardation, seizures, hypotonia that evolved into spasticity, and feeding difficulties. Clinical and laboratory studies demonstrated etiologic heterogeneity. Molecular studies detected microdeletions in chromosome band 17p13.3 in six of 44 patients tested, confirming that deletion of all or part of this "critical region" is the cause of ILS in some cases. There were slightly larger deletions in the same region in a majority of patients with Miller-Dieker syndrome. One patient had an apparently balanced, de novo reciprocal translocation with breakpoints at Xq22 and 2p25. Four sibs from two families had a new, autosomal recessive syndrome of ILS with neonatal death. Other causes supported by clinical observations include autosomal recessive inheritance, intrauterine infection, and intrauterine perfusion failure. Those ILS probands in whom no etiology could be established had 41 sibs of whom three were affected, giving an empiric recurrence risk of 7%.