Absence of pericentromeric heterochromatin (9qh-) in a patient with bilateral retinoblastoma

Heteromorphic variants of chromosome 9

Background

Heterochromatic variants of pericentromere of chromosome 9 are reported and discussed since decades concerning their detailed structure and clinical meaning. However, detailed studies are scarce. Thus, here we provide the largest ever done molecular cytogenetic research based on >300 chromosome 9 heteromorphism carriers.

Results

In this study, 334 carriers of heterochromatic variants of chromosome 9 were included, being 192 patients from Western Europe and the remainder from Easter-European origin. A 3-color-fluorescence in situ hybridization (FISH) probe-set directed against for 9p12 to 9q13~21.1 (9het-mix) and 8 different locus-specific probes were applied for their characterization. The 9het-mix enables the characterization of 21 of the yet known 24 chromosome 9 heteromorphic patterns. In this study, 17 different variants were detected including five yet unreported; the most frequent were pericentric inversions (49.4%) followed by 9qh-variants (23.9%), variants of 9ph (11.4%), cenh (8.2%), and dicentric- (3.8%) and duplication-variants (3.3%). For reasons of simplicity, a new short nomenclature for the yet reported 24 heteromorphic patterns of chromosome 9 is suggested. Six breakpoints involved in four of the 24 variants could be narrowed down using locus-specific probes.

Conclusions

Based on this largest study ever done in carriers of chromosome 9 heteromorphisms, three of the 24 detailed variants were more frequently observed in Western than in Eastern Europe. Besides, there is no clear evidence that infertility is linked to any of the 24 chromosome 9 heteromorphic variants.

pRb2/p130: a new candidate for retinoblastoma tumor formation

Retinoblastoma is the most common primary intraocular tumor in childhood. Mutations in both the alleles of the RB1 gene represent the causative agent for the tumor to occur. It is becoming evident that, although these alterations represent key events in the genesis of retinoblastoma, they are not sufficient per se for the tumor to develop, and other additional genetic or epigenetic alterations must occur. A supportive role in the genesis of retinoblastoma has recently been proposed for the RB1-related gene RB2/p130. Additionally, several other genetic alterations involving different chromosomes have been described as relevant in the tumorigenic process. In this review we will analyse current knowledge about the molecular mechanisms involved in retinoblastoma, paying particular attention to the mechanisms of inactivation of the biological function of the retinoblastoma family of proteins.

Caudal dysplasia sequence with penile enlargement: case report and a potential pathogenic hypothesis

The clinical spectrum of caudal dysplasia sequence (CDS) is noted for its diversity. The origin of CDS remains unknown, though poorly controlled gestational diabetes has been implicated in some cases. Here we describe the case of a newborn with CDS associated with penile enlargement (PE). The main anomalies included anal atresia, agenesis of the kidneys and of the sacrococcygeal vertebrae, dysgenesis of lumbar vertebrae, and bilateral cryptorchidism. Penile enlargement (7 cm), a rather unusual finding, has so far not been reported in association with CDS. Chromosomal analysis failed, and the neonate died 30 min after birth. Comparative genomic hybridization analysis using stored DNA showed a balanced normal male DNA content, which negates chromosomal losses or gains as a cause of CDS and/or PE. PE due to virilizing-type adrenal hyperplasia, caused by common mutations in the genes encoding for the adrenal enzymes 21-hydroxylase and 11-hydroxylase, was ruled out. We report on a previously unpublished case of the coexistence of PE and severe CDS and propose a possible pathogenetic hypothesis of this association.