A unique point mutation in the PMP22 gene is associated with Charcot-Marie-Tooth disease and deafness.

Charcot-Marie-Tooth disease (CMT) with deafness is clinically distinct among the genetically heterogeneous group of CMT disorders. Molecular studies in a large family with autosomal dominant CMT and deafness have not been reported. The present molecular study involves a family with progressive features of CMT and deafness, originally reported by Kousseff et al. Genetic analysis of 70 individuals (31 affected, 28 unaffected, and 11 spouses) revealed linkage to markers on chromosome 17p11.2-p12, with a maximum LOD score of 9.01 for marker D17S1357 at a recombination fraction of .03. Haplotype analysis placed the CMT-deafness locus between markers D17S839 and D17S122, a approximately 0.6-Mb interval. This critical region lies within the CMT type 1A duplication region and excludes MYO15, a gene coding an unconventional myosin that causes a form of autosomal recessive deafness called DFNB3. Affected individuals from this family do not have the common 1.5-Mb duplication of CMT type 1A. Direct sequencing of the candidate peripheral myelin protein 22 (PMP22) gene detected a unique G-->C transversion in the heterozygous state in all affected individuals, at position 248 in coding exon 3, predicted to result in an Ala67Pro substitution in the second transmembrane domain of PMP22.

Prevalence of 22q11 region deletions in patients with velopharyngeal insufficiency.

Velo-cardio-facial syndrome, DiGeorge syndrome, conotruncal anomaly face syndrome, tetralogy of Fallot, and pulmonary atresia with ventricular septal defect are all associated with hemizygosity of 22q11. While the prevalence of the deletions in these phenotypes has been studied, the frequency of deletions in patients presenting with velopharyngeal insufficiency (VPI) is unknown. We performed fluorescence in situ hybridization for locus D22S75 within the 22q11 region on 23 patients with VPI (age range 5-42 years) followed in the Craniofacial Clinic at the University of Florida. The VPI occurred either as a condition of unknown cause (n=16) or as a condition remaining following primary cleft palate surgery (n=7). Six of sixteen patients with VPI of unknown cause and one of seven with VPI following surgery had a deletion in the region. This study documents a high frequency of 22q11 deletions in those presenting with VPI unrelated to overt cleft palate surgery and suggests that deletion testing should be considered in patients with VPI.