Refinement of the critical 2p25.3 deletion region: the role of MYT1L in intellectual disability and obesity

PURPOSE

Submicroscopic deletions of chromosome band 2p25.3 are associated with intellectual disability and/or central obesity. Although MYT1L is believed to be a critical gene responsible for intellectual disability, so far no unequivocal data have confirmed this hypothesis.

METHODS

In this study we evaluated a cohort of 22 patients (15 sporadic patients and two families) with a 2p25.3 aberration to further refine the clinical phenotype and to delineate the role of MYT1L in intellectual disability and obesity. In addition, myt1l spatiotemporal expression in zebrafish embryos was analyzed by quantitative polymerase chain reaction and whole-mount in situ hybridization.

RESULTS

Complete MYT1L deletion, intragenic deletion, or duplication was observed in all sporadic patients, in addition to two patients with a de novo point mutation in MYT1L. The familial cases comprise a 6-Mb deletion in a father and his three children and a 5' MYT1L overlapping duplication in a father and his two children. Expression analysis in zebrafish embryos shows specific myt1l expression in the developing brain.

CONCLUSION

Our data strongly strengthen the hypothesis that MYT1L is the causal gene for the observed syndromal intellectual disability. Moreover, because 17 patients present with obesity/overweight, haploinsufficiency of MYT1L might predispose to weight problems with childhood onset.Genet Med 17 6, 460-466.

Further delineation of the 15q13 microdeletion and duplication syndromes: a clinical spectrum varying from non-pathogenic to a severe outcome

BACKGROUND

Recurrent 15q13.3 microdeletions were recently identified with identical proximal (BP4) and distal (BP5) breakpoints and associated with mild to moderate mental retardation and epilepsy.

METHODS

To assess further the clinical implications of this novel 15q13.3 microdeletion syndrome, 18 new probands with a deletion were molecularly and clinically characterised. In addition, we evaluated the characteristics of a family with a more proximal deletion between BP3 and BP4. Finally, four patients with a duplication in the BP3-BP4-BP5 region were included in this study to ascertain the clinical significance of duplications in this region.

RESULTS

The 15q13.3 microdeletion in our series was associated with a highly variable intra- and inter-familial phenotype. At least 11 of the 18 deletions identified were inherited. Moreover, 7 of 10 siblings from four different families also had this deletion: one had a mild developmental delay, four had only learning problems during childhood, but functioned well in daily life as adults, whereas the other two had no learning problems at all. In contrast to previous findings, seizures were not a common feature in our series (only 2 of 17 living probands). Three patients with deletions had cardiac defects and deletion of the KLF13 gene, located in the critical region, may contribute to these abnormalities. The limited data from the single family with the more proximal BP3-BP4 deletion suggest this deletion may have little clinical significance. Patients with duplications of the BP3-BP4-BP5 region did not share a recognisable phenotype, but psychiatric disease was noted in 2 of 4 patients.

CONCLUSIONS

Overall, our findings broaden the phenotypic spectrum associated with 15q13.3 deletions and suggest that, in some individuals, deletion of 15q13.3 is not sufficient to cause disease. The existence of microdeletion syndromes, associated with an unpredictable and variable phenotypic outcome, will pose the clinician with diagnostic difficulties and challenge the commonly used paradigm in the diagnostic setting that aberrations inherited from a phenotypically normal parent are usually without clinical consequences.

Meier-Gorlin syndrome: report of eight additional cases and review

The Meier-Gorlin syndrome or ear, patella, short stature syndrome (MIM 224690) is a rare autosomal recessive disorder, characterized by the association of bilateral microtia, aplasia/hypoplasia of the patellae, and severe pre- and postnatal growth retardation. Twenty-one cases have been reported in literature thus far. Here we report on eight patients from seven families and compare them with previously described cases. One of the present cases had previously undescribed genital anomalies. There is a difference in facial characteristics between patients reported in early infancy and those described at older age; follow-up of patients is needed to substantiate this changing facial phenotype. We recommend radiographic survey of the patellae in patients at older age to investigate the weight of absent or hypoplastic patellae in the diagnosis of the syndrome.

Diagnosis and treatment of the Pierre Robin sequence: results of a retrospective clinical study and review of the literature

We performed a retrospective study of all children with Pierre Robin sequence (PRS), admitted to our hospital from 1981-1998 in order to evaluate diagnosis, treatment and prognosis. Patients were divided into two categories: isolated PRS (group 1) and PRS plus, i.e. PRS as part of a more complex syndrome (group 2). A total of 74 patients with PRS were found, 29 (39%) males and 45 (61%) females of whom 47 (63.5%) could be categorised as isolated PRS and 27 (36.8%) as PRS plus. The most frequent diagnoses in patients with PRS plus were Stickler syndrome and the velocardiofacial syndrome. Ophthalmological and fluorescent in situ hybridisation of chromosome 22 investigations should therefore be performed in all patients, as soon as the diagnosis of PRS is established. Some form of airway treatment was necessary in the majority of patients (52 of 74), most could be treated conservatively with prone/lateral positioning and close observation. Endotracheal intubation was necessary in one child from group 1 versus five from group 2. Tracheostomy was performed in three children from group 1 and two from group 2. Feeding problems occurred in about 25% of all PRS patients and stunted growth was seen especially in boys with isolated PRS before the age of 10 months.

CONCLUSION

In our series, 33% of patients with Pierre Robin sequence plus had Stickler and velocardiofacial syndromes. Conservative airway management was a sufficient treatment for respiratory problems in the majority of patients. Feeding and growth need special attention in patients with Pierre Robin sequence.

Clonal origin of trisomy for chromosome 7 in the epithelial compartment of colon neoplasia

In this study, we demonstrated the clonal origin of trisomy for chromosome 7 in epithelial cells of colon neoplasia. By using the double-target fluorescence in situ hybridization (FISH) technique in frozen tissue sections that were also immunostained for keratin and vimentin, ratio analysis of FISH signals for chromosomes 7 and 17 could be performed in epithelial (cytokeratin-positive) or stromal (vimentin-positive) areas. The data demonstrated that trisomy for chromosome 7 is found exclusively in the epithelial compartments and not in the stroma of colon adenocarcinoma. We then demonstrated the occurrence of trisomy for chromosome 7 in the different types of epithelial neoplastic cells, i.e., columnar and goblet cells, which were isolated from frozen tissue sections by mechanical disaggregation of colon tissue and mild lysis of the cells while protease activity was inhibited. In these cell suspensions, the columnar cells were detected with an antibody to villin, and the goblet cells were stained for mucin, whereas all cells were subsequently subjected to FISH for chromosome 7. For analysis of neuroendocrine cells, which are present in a very low frequency in colon neoplasia, frozen tissue sections that were immunostained for Chromogranin A could be used. Individual neuroendocrine cells could be distinguished in these thin frozen tissue sections. The presence of trisomy for chromosome 7 in all three different epithelial cell types strengthens our suggestion that this chromosomal aberration is found in the epithelial stem cell compartment of colon neoplasia.