Complex small supernumerary marker chromosomes (sSMC) constitute one of the smallest subgroups of sSMC in general. Complex sSMC consist of chromosomal material derived from more than one chromosome; the best known representative of this group is the derivative chromosome 22 {der(22)t(11;22)} or Emanuel syndrome. In 2008 we speculated that complex sSMC could be part of an underestimated entity. Here, the overall yet reported 412 complex sSMC are summarized. They constitute 8.4% of all yet in detail characterized sSMC cases. The majority of the complex sSMC is contributed by patients suffering from Emanuel syndrome (82%). Besides there are a der(22)t(8;22)(q24.1;q11.1) and a der(13)t(13;18)(q11;p11.21) or der(21)t(18;21)(p11.21;q11.1) = der(13 or 21)t(13 or 21;18) syndrome. The latter two represent another 2.6% and 2.2% of the complex sSMC-cases, respectively. The large majority of complex sSMC has a centric minute shape and derives from an acrocentric chromosome. Nonetheless, complex sSMC can involve material from each chromosomal origin. Most complex sSMC are inherited form a balanced translocation in one parent and are non-mosaic. Interestingly, there are hot spots for the chromosomal breakpoints involved. Complex sSMC need to be considered in diagnostics, especially in non-mosaic, centric minute shaped sSMC. As yet three complex-sSMC-associated syndromes are identified. As recurrent breakpoints in the complex sSMC were characterized, it is to be expected that more syndromes are identified in this subgroup of sSMC. Overall, complex sSMC emphasize once more the importance of detailed cytogenetic analyses, especially in patients with idiopathic mental retardation.

Nijmegen breakage syndrome (NBS) is a rare DNA repair disorder characterized by microcephaly, immunodeficiency, and predisposition to malignancy. We report on a 5-year-old patient with NBS who presented with nodular sclerosing type of Hodgkin disease stage IVB. Chemotherapy consisting of COPP/ABV regimen with reduction at 75% of full doses was employed. During this treatment, no major toxic or infectious complications were observed. Complete remission was achieved lasting now for 20 months. In DNA repair disorders, prognosis of Hodgkin disease is poor as opposed to excellent overall prognosis in general pediatric population. Better survival may be achieved both with adopted, disease-specific regimens, and individualized approach considering patient's clinical condition. Also, better recognition and treatment of infections during chemotherapy may reduce early deaths in patients with DNA repair disorders.

Patients with Angelman syndrome (AS) are affected by severe intellectual disability with absence of speech, distinctive dysmorphic craniofacial features, ataxia and a characteristic behavioral phenotype. AS is caused by the lack of expression in neurons of the UBE3A gene, which is located in the 15q11.2-q13 imprinted region. Functional loss of UBE3A is due to 15q11.2-q13 deletion, mutations in the UBE3A gene, paternal uniparental disomy and genomic imprinting defects. We report here two patients with clinical features of AS referred to our hospital for clinical follow-up and genetic diagnosis. Methylation Specific-Multiplex Ligation-Dependent Probe Amplification (MS-MLPA) of the 15q11.2-q13 region was carried out in our laboratory as the first diagnostic tool detecting two novel UBE3A intragenic deletions. Subsequently, the MLPA P336-A2 kit was used to confirm and determine the size of the UBE3A deletion in the two patients. A review of the clinical features of previously reported patients with whole UBE3A gene or partial intragenic deletions is presented here together with these two new patients. Although rare, UBE3A intragenic deletions may represent a small fraction of AS patients without a genetic diagnosis. Testing for UBE3A intragenic exonic deletions should be performed in those AS patients with a normal methylation pattern and no mutations in the UBE3A gene.

Spinal muscular atrophy (SMA) is the second most frequent autosomal recessive disease characterized by degeneration of the anterior horn cells of the spinal cord, leading to muscular atrophy. SMA is classified into three types according to disease severity and age-onset: severe (type I), intermediate (type II) and mild (type III). Deletions in the survival motor neuron (SMN) gene, located in the chromosome region 5q11.2- 5q13.3, are major determinants of SMA phenotype. Extended deletions that include the neuronal apoptosis inhibitory protein (NAIP) gene may correlate with the severtity of SMA. SMN gene is present in two highly homologous copies, SMN1 and SMN2, but only deletions of the SMN1 gene (exons 7 and 8 or exon 7) are responsible for clinical manifestations of SMA. Here, we present the deletion profiling of SMN1 and NAIP genes in 89 children with SMA from Serbia: 52 patients with type I, 26 with type II, and 11 with type III. The homozygous deletion of the SMN1 gene was confirmed in 72 of 89 (81%) patients, being the most frequent in SMA type I (48/52): 68 patients (94.4%) with deletion of exons 7 and 8 and 4 patients (5.6%) with deletion of exon 7. The extended deletion including the NAIP gene was detected in 18 of 89 (20.2%) patients, mostly affected with type I. This study has revealed the lower incidence of deletions in the SMN1 and NAIP genes in families with SMA in Serbia and will provide important information for genetic counselling in these families.

The high sensitivity of Fanconi's anemia (FA) cells to drug induced DNA interstrand crosslinks (ICL) such as diepoxybutane (DEB) was used as a part of FA screening in the children with clinical suspicion of FA. The study considered a total of 66 children with the hematological and/or congenital phenotypic symptoms reminiscent of FA. Blood samples from patients with clinical suspicion of FA and controls were collected for chromosome fragility evaluation by the DEB test. According to the results of DEB test, the patients were divided into two subgroups: FA displaying typical DEB sensitive cellular response and non FA. In this study, 10 out of 66 patients were found to have a FA cellular phenotype. The percentage of DEB-induced aberrant cells was increased more than 26 times in FA patients (range 22.00-82.00% with a mean of 48.32%) when compared to non FA patients (range 0.00-12.00% with a mean of 1.84%). The number of DEB-induced breaks/cells was more than 68 times higher in FA patients (range 0.26-4.39 with a mean of 1.37 breaks/cell) when compared to non FA patients (range 0.00-0.20 with a mean of 0.02 breaks/cell). The spontaneous chromosome fragility values in FA patients were overlapping those in non FA patients. Our results indicate that the DEB sensitivity test is the most reliable in vitro method for verification of the FA cellular phenotype.