Subterminal deletion/duplication event in an affected male due to maternal X chromosome pericentric inversion

IRAK1 Duplication in MECP2 Duplication Syndrome Does Not Increase Canonical NF-κB-Induced Inflammation

PURPOSE

Besides their developmental and neurological phenotype, most patients with MECP2/IRAK1 duplication syndrome present with recurrent and severe infections, accompanied by strong inflammation. Respiratory infections are the most common cause of death. Standardized pneumological diagnostics, targeted anti-infectious treatment, and knowledge of the underlying pathomechanism that triggers strong inflammation are unmet clinical needs. We investigated the influence of IRAK1 overexpression on the canonical NF-κB signaling as a possible cause for excessive inflammation in these patients.

METHODS

NF-κB signaling was examined by measuring the production of proinflammatory cytokines and evaluating the IRAK1 phosphorylation and degradation as well as the IκBα degradation upon stimulation with IL-1β and TLR agonists in SV40-immortalized fibroblasts, PBMCs, and whole blood of 9 patients with MECP2/IRAK1 duplication syndrome, respectively.

RESULTS

Both, MECP2/IRAK1-duplicated patients and healthy controls, showed similar production of IL-6 and IL-8 upon activation with IL-1β and TLR2/6 agonists in immortalized fibroblasts. In PBMCs and whole blood, both patients and controls had a similar response of cytokine production after stimulation with IL-1β and TLR4/2/6 agonists. Patients and controls had equivalent patterns of IRAK1 phosphorylation and degradation as well as IκBα degradation upon stimulation with IL-1β.

CONCLUSION

Patients with MECP2/IRAK1 duplication syndrome do not show increased canonical NF-κB signaling in immortalized fibroblasts, PBMCs, and whole blood. Therefore, we assume that these patients do not benefit from a therapeutic suppression of this pathway.

Cytogenetic and molecular characterization of a recombinant X chromosome in a family with a severe neurologic phenotype and macular degeneration

Background

Duplications of MECP2 gene in males cause a syndrome characterized by distinctive clinical features, including severe to profound mental retardation, infantile hypotonia, mild dysmorphic features, poor speech development, autistic features, seizures, progressive spasticity and recurrent infections. Patients with complex chromosome rearrangements, leading to Xq28 duplication, share most of the clinical features of individuals with tandem duplications, in particular neurologic problems, suggesting a major pathogenetic role of MECP2 overexpression.

Results

We performed cytogenetic and molecular cytogenetic studies in a previously described family with affected males showing congenital ataxia, late-onset progressive myoclonic encephalopathy and selective macular degeneration. Microsatellite, FISH and array-CGH analyses identified a recombinant X chromosome with a deletion of the PAR1 region, encompassing SHOX, replaced by a duplicated segment of the Xq28 terminal portion, including MECP2.

Conclusions

Our report describes the identification of the actual genetic cause underlying a severe syndrome that previous preliminary analyses erroneously associated to a terminal Xp22.33 region. In the present family as well as in previously reported patients with similar rearrangements, the observed neurologic phenotype is ascribable to MECP2 duplication, with an undefined contribution of the other involved genes. Maculopathy, presented by affected males reported here, could be a novel clinical feature associated to Xq28 disomy due to recombinant X chromosomes, but at present the underlying pathogenetic mechanism is unknown and this potential clinical correlation should be confirmed through the collection of additional patients.

MECP2 duplications in six patients with complex sex chromosome rearrangements

Duplications of the Xq28 chromosome region resulting in functional disomy are associated with a distinct clinical phenotype characterized by infantile hypotonia, severe developmental delay, progressive neurological impairment, absent speech, and proneness to infections. Increased expression of the dosage-sensitive MECP2 gene is considered responsible for the severe neurological impairments observed in affected individuals. Although cytogenetically visible duplications of Xq28 are well documented in the published literature, recent advances using array comparative genomic hybridization (CGH) led to the detection of an increasing number of microduplications spanning MECP2. In rare cases, duplication results from intrachromosomal rearrangement between the X and Y chromosomes. We report six cases with sex chromosome rearrangements involving duplication of MECP2. Cases 1-4 are unbalanced rearrangements between X and Y, resulting in MECP2 duplication. The additional Xq material was translocated to Yp in three cases (cases 1-3), and to the heterochromatic region of Yq12 in one case (case 4). Cases 5 and 6 were identified by array CGH to have a loss in copy number at Xp and a gain in copy number at Xq28 involving the MECP2 gene. In both cases, fluorescent in situ hybridization (FISH) analysis revealed a recombinant X chromosome containing the duplicated material from Xq28 on Xp, resulting from a maternal pericentric inversion. These cases add to a growing number of MECP2 duplications that have been detected by array CGH, while demonstrating the value of confirmatory chromosome and FISH studies for the localization of the duplicated material and the identification of complex rearrangements.

Identification and characterization of different SHOX gene deletions in patients with Leri-Weill dyschondrosteosys by MLPA assay

Deletions of the SHOX gene (Xp22-Yp11.3) are associated with Leri-Weill dyschondrosteosys (LWD) and idiopathic short stature. It has been estimated that SHOX deletions occur in 1,000-2,000 individuals in the total population, suggesting that this alteration should be investigated in all cases with unexplained short stature. SHOX deletions are currently investigated using fluorescence in situ hybridization (FISH) or molecular analysis of intragenic CA repeats. However, both techniques show some limitations. In the present study, the use of the multiple ligation probe amplification (MLPA) assay for the identification and characterization of SHOX deletions in 15 LWD patients, 3 of which carriers of chromosome abnormalities involving the SHOX gene, is reported. MLPA analysis demonstrated the heterozygous deletion of SHOX in seven patients (46.6%), disclosing the presence of two different proximal breakpoints. In patients with abnormal karyotype, MLPA analysis was able to identify the chromosomal rearrangement, showing, in addition to the SHOX deletions, the gain or loss of other genes mapped on the X and Y chromosomes. Since MLPA analysis can be carried out on a simple buccal swab, avoiding invasive peripheral blood collection, this technique represents a fast, simple and high throughput approach in the screening of SHOX deletions, able to provide more information as compared to FISH and microsatellite analysis.

Duplication of the MECP2 region is a frequent cause of severe mental retardation and progressive neurological symptoms in males

Loss-of-function mutations of the MECP2 gene at Xq28 are associated with Rett syndrome in females and with syndromic and nonsyndromic forms of mental retardation (MR) in males. By array comparative genomic hybridization (array-CGH), we identified a small duplication at Xq28 in a large family with a severe form of MR associated with progressive spasticity. Screening by real-time quantitation of 17 additional patients with MR who have similar phenotypes revealed three more duplications. The duplications in the four patients vary in size from 0.4 to 0.8 Mb and harbor several genes, which, for each duplication, include the MR-related L1CAM and MECP2 genes. The proximal breakpoints are located within a 250-kb region centromeric of L1CAM, whereas the distal breakpoints are located in a 300-kb interval telomeric of MECP2. The precise size and location of each duplication is different in the four patients. The duplications segregate with the disease in the families, and asymptomatic carrier females show complete skewing of X inactivation. Comparison of the clinical features in these patients and in a previously reported patient enables refinement of the genotype-phenotype correlation and strongly suggests that increased dosage of MECP2 results in the MR phenotype. Our findings demonstrate that, in humans, not only impaired or abolished gene function but also increased MeCP2 dosage causes a distinct phenotype. Moreover, duplication of the MECP2 region occurs frequently in male patients with a severe form of MR, which justifies quantitative screening of MECP2 in this group of patients.