Chromosome deletions in 13q33-34: report of four patients and review of the literature.

Deletions of chromosome bands 13q33-34 are rare. Patients with such deletions have mental retardation, microcephaly, and distinct facial features. Male patients frequently also have genital malformations. We report on four patients with three overlapping deletions of 13q33-34 that have been characterized by tiling-path array-CGH. Patient 1 had mental retardation and microcephaly with an interstitial 4.7 Mb deletion and a translocation t(12;13)(q13.3;q32.3). His mother (Patient 2), who also had mental retardation and microcephaly, carried the identical chromosome aberration. Patient 3 was a girl with a de novo insertion ins(7;13)(p15.1;q22q31) and interstitial 4.5 Mb deletion in 13q33-34. She had mental retardation and microcephaly. Patient 4 was a newborn boy with severe genital malformation (penoscrotal transposition and hypospadias) and microcephaly. He had a de novo ring chromosome 13 lacking the terminal 9.3 Mb of 13q. Karyotype-phenotype comparisons of these and eight previously published del13q33-34 patients suggest EFNB2 as a candidate gene for genital malformations in males. Molecular cytogenetic definition of a common deleted region in all patients suggests ARHGEF7 as a candidate gene for mental retardation and microcephaly.

Thirty-two new cases with small supernumerary marker chromosomes detected in connection with fertility problems: detailed molecular cytogenetic characterization and review of the literature.

Thirty-two patients with fertility problems were identified as carriers of small supernumerary marker chromosomes (sSMC). Molecular cytogenetic techniques were used to characterize their chromosomal origin. Together with the other cases available in the literature 111 sSMC cases have now been detected in connection with fertility problems in otherwise clinically healthy persons and characterized for their genetic content. According to this study, in 60% of the cases the sSMC originated from chromosomes 14 or 15. Euchromatic imbalances were caused by the sSMC presence in 30% of the cases. Notably, in 53% of infertile sSMC carriers, the sSMC was parentally transmitted. As we found indications of an as yet unknown mechanism for the elimination of sSMC from the human gene pool, sSMC could also play a role in elucidating the process of chromosome gain and loss during evolution. Nonetheless, further detailed molecular analysis will be necessary in the future to characterize the mechanisms and genetic basis for this phenomenon.

De novo t(12;17)(p13.3;q21.3) translocation with a breakpoint near the 5' end of the HOXB gene cluster in a patient with developmental delay and skeletal malformations.

A boy with severe mental retardation, funnel chest, bell-shaped thorax, and hexadactyly of both feet was found to have a balanced de novo t(12;17)(p13.3;q21.3) translocation. FISH with BAC clones and long-range PCR products assessed in the human genome sequence localized the breakpoint on chromosome 17q21.3 to a 21-kb segment that lies <30 kb upstream of the HOXB gene cluster and immediately adjacent to the 3' end of the TTLL6 gene. The breakpoint on chromosome 12 occurred within telomeric hexamer repeats and, therefore, is not likely to affect gene function directly. We propose that juxtaposition of the HOXB cluster to a repetitive DNA domain and/or separation from required cis-regulatory elements gave rise to a position effect.

New cytogenetically visible copy number variant in region 8q21.2.

BACKGROUND: Cytogenetically visible unbalanced chromosomal abnormalities (UBCA), reported for >50 euchromatic regions of almost all human autosomes, are comprised of a few megabases of DNA, and carriers are in many cases clinically healthy. It may be speculated, that some of the UBCA may be similar or identical to copy number variants (CNV) of the human genome. RESULTS: Here we report on a yet unreported cytogenetically visible copy number variant (CNV) in the long arm of chromosome 8, region 8q21.2, detected in three unrelated clinically healthy carriers. CONCLUSION: The first description of a cytogenetically visible CNV/UBCA in 8q21.2 shows that banding cytogenetics is far from being outdated. It is a cost efficient, up-to-date method for a single cell specific overview on the whole genome, still prepared to deliver unexpected findings.

Blepharophimosis-ptosis-epicanthus inversus syndrome in a girl with chromosome translocation t(2;3)(q33;q23).

We report on a young female patient with the clinical features of blepharophimosis-ptosis-epicanthus inversus syndrome (BPES, OMIM 110100) and a balanced chromosome translocation 46, XX, t(2;3)(q33;q23)dn.BPES is a rare autosomal dominant congenital disorder characterized by the eponymous oculo-facial features that are, in female patients, associated either with (type 1 BPES) or without (type 2 BPES) premature ovarian failure. Both types of BPES are caused by heterozygous mutations in the FOXL2 gene, which is located in chromosome band 3q23. Chromosome aberrations such as balanced rearrangements have only rarely been observed in BPES patients but can provide valuable information about regulatory regions of FOXL2. The translocation in this patient broadens our knowledge of pathogenic mechanisms in BPES and highlights the importance of conventional cytogenetic investigations in patients with negative results of FOXL2 mutation screening as a prerequisite for optimal management and genetic counseling.

A multiple translocation event in a patient with hexadactyly, facial dysmorphism, mental retardation and behaviour disorder characterised comprehensively by molecular cytogenetics. Case report and review of the literature.

UNLABELLED: We report a 13-year-old female patient with multiple congenital abnormalities (microcephaly, facial dysmorphism, anteverted dysplastic ears and postaxial hexadactyly), mental retardation, and adipose-gigantism. Ultrasonography revealed no signs of a heart defect or renal abnormalities. She showed no speech development and suffered from a behavioural disorder. CNS abnormalities were excluded by cerebral MRI. Initial cytogenetic studies by Giemsa banding revealed an aberrant karyotype involving three chromosomes, t(2;4;11). By high resolution banding and multicolour fluoresence in-situ hybridisation (M-FISH, MCB), chromosome 1 was also found to be involved in the complex chromosomal aberrations, confirming the karyotype 46,XX,t(2;11;4).ish t(1;4;2;11)(q43;q21.1;p12-p13.1;p14.1). To the best of our knowledge no patient has been previously described with such a complex translocation involving 4 chromosomes. This case demonstrates that conventional chromosome banding techniques such as Giemsa banding are not always sufficient to characterise complex chromosomal abnormalities. Only by the additional utilisation of molecular cytogenetic techniques could the complexity of the present chromosomal rearrangements and the origin of the involved chromosomal material be detected. Further molecular genetic studies will be performed to clarify the chromosomal breakpoints potentially responsible for the observed clinical symptoms. CONCLUSION: This report demonstrates that multicolour-fluorescence in-situ hybridisation studies should be performed in patients with congenital abnormalities and suspected aberrant karyotypes in addition to conventional Giemsa banding.