Pathogenesis and characteristics of large ameloblastoma of the jaw: a report of two rare cases

Ameloblastoma is a common odontogenic epithelial tumor that exhibits various biological behaviors, ranging from simple cystic expansion to aggressive solid masses characterized by local invasiveness, a high risk of recurrence, and even malignant transformation. We report on two cases of unusually large solid ameloblastomas. We detected epithelial–mesenchymal transition-related gene expression and HRAS gene single nucleotide polymorphisms, providing possible molecular evidence of mesenchymal morphological changes in ameloblastoma. The detailed analysis of the pathogenesis of these two cases of ameloblastoma may deepen our understanding of this rare disease and offer promising targets for future targeted therapy.

Phacomatosis Pigmentokeratotica

In the group of the epidermal nevus syndromes, Happle defined in 1996 a separate entity characterized by the presence of an organoid epidermal nevus, sometimes showing sebaceous differentiation, and a speckled lentiginous nevus of the papular type, occasionally associated with extracutaneous anomalies including neurological, ophthalmological, and skeletal abnormalities. In particular, the syndrome is associated with mental retardation, epilepsy, deafness, hemiatrophy, dysesthesia, and hyperhidrosis, strabismus, lipodermoid of conjunctiva, coloboma and ptosis, and kyphosis, scoliosis, limb asymmetry, and hypertrophy. Rarely, hypertension, vascular abnormalities, atrioventricular block, hypophosphatemic rickets, and pheochromocytoma may occur. The organoid nevus follows the lines of Blaschko whereas the speckled lentiginous nevus is arranged in a checkerboard pattern. For this syndrome, the term “Phacomatosis Pigmentokeratotica” has been coined and, at the present, it is considered a very rare clinical entity, with less than 20 cases reported in the literature. Recent genetic findings have included this syndrome in the group of the mosaic RASopathies, after the discovery of mutations in the HRAS gene occurring in both sebaceous and vascular nevi, but not in nonaffected tissues.

Costello Syndrome with Severe Nodulocystic Acne: Unexpected Significant Improvement of Acanthosis Nigricans after Oral Isotretinoin Treatment

We report the case of 17-year-old female diagnosed with Costello syndrome. Genetic testing provided a proof with G12S mutation in the HRAS gene since 3 years of age with a presentation of severe nodulocystic acne on her face. After 2 months of oral isotretinoin treatment, improvement in her acne was observed. Interestingly, an unexpected significant improvement of acanthosis nigricans on her neck and dorsum of her hands was found as well. We present this case as a successful treatment option by using oral isotretinoin for the treatment of acanthosis nigricans in Costello syndrome patients.

Polymerase ζ activity is linked to replication timing in humans: evidence from mutational signatures

Replication timing is an important determinant of germline mutation patterns, with a higher rate of point mutations in late replicating regions. Mechanisms underlying this association remain elusive. One of the suggested explanations is the activity of error-prone DNA polymerases in late-replicating regions. Polymerase ζ (pol ζ), an essential error-prone polymerase biased towards transversions, also has a tendency to produce dinucleotide mutations (DNMs), complex mutational events that simultaneously affect two adjacent nucleotides. Experimental studies have shown that pol ζ is strongly biased towards GC->AA/TT DNMs. Using primate divergence data, we show that the GC->AA/TT pol ζ mutational signature is the most frequent among DNMs, and its rate exceeds the mean rate of other DNM types by a factor of ~10. Unlike the overall rate of DNMs, the pol ζ signature drastically increases with the replication time in the human genome. Finally, the pol ζ signature is enriched in transcribed regions, and there is a strong prevalence of GC->TT over GC->AA DNMs on the non-template strand, indicating association with transcription. A recurrently occurring GC->TT DNM in HRAS gene causes the Costello syndrome; we find a 2-fold increase in the mutation rate, and a 2-fold decrease in the transition/transversion ratio, at distances of up to 1 kb from the DNM, suggesting a link between the Costello syndrome and pol ζ activity. This study uncovers the genomic preferences of pol ζ, shedding light on a novel cause of mutational heterogeneity along the genome.