Kohlschutter-Tonz Syndrome: Clinical and Genetic Insights Gained From 16 Cases Deriving From a Close-Knit Village in Northern Israel

BACKGROUND: Kohlschutter-Tonz syndrome (KTS; MIM 22675) is a rare autosomal recessive disorder characterized by intellectual impairment, spasticity, epilepsy, and amelogenesis imperfecta. We have recently identified the causative gene and mutation underlying KTS, namely, p.R157X, corresponding to ROGDI c.571C>T, which creates a premature stop codon in ROGDI homolog (Drosophila), a gene of unknown function, in KTS patients of Druze origin. PATIENTS: To better delineate the phenotype of KTS, 16 cases (eight female, eight male), from seven families (five kindreds) originating from a Druze village in Northern Israel, all homozygous for the same deleterious mutation, were investigated. Medical records were reviewed, and a detailed medical history was obtained by interview of parents. RESULTS: Age at onset between six and 12 months of age and the intensity of convulsions were variably manifested by affected sibs and mirror the progression of mental and motor deterioration. Amelogenesis imperfecta and deficient speech occur in all cases. By late adolescence and early twenties, individuals with KTS are bedridden, fed by a gastrostomy tube, spastic, and practically have no cognitive and language perception. CONCLUSIONS: KTS, a genetic disease heralded by convulsions, "yellow teeth," and severe mental impairment, allows for a clinical variability as regarding age of onset and severity of seizures that per se predict the speed of mental deterioration. In all cases, however, the morbid course of the disease is ultimately equally devastating by the twenties

A Nonsense Mutation in the Human Homolog of Drosophila rogdi Causes Kohlschutter-Tonz Syndrome

Kohlschutter-Tonz syndrome (KTS) is a rare autosomal-recessive disorder of childhood onset, and it is characterized by global developmental delay, spasticity, epilepsy, and amelogenesis imperfecta. In 12 KTS-affected individuals from a Druze village in northern Israel, homozygosity mapping localized the gene linked to the disease to a 586,513 bp region (with a LOD score of 6.4) in chromosomal region 16p13.3. Sequencing of genes (from genomic DNA of an affected individual) in the linked region revealed chr16: 4,848,632 G>A, which corresponds to ROGDIc.469C>T (p.Arg157*). The nonsense mutation was homozygous in all affected individuals, heterozygous in 10 of 100 unaffected individuals from the same Druze community, and absent from Druze controls from elsewhere. Wild-type ROGDI localizes to the nuclear envelope; ROGDI was not detectable in cells of affected individuals. All affected individuals suffered seizures, were unable to speak, and had amelogenesis imperfecta. However, age of onset and the severity of mental and motor handicaps and that of convulsions varied among affected individuals homozygous for the same nonsense allele