Paolo Prontera

Mutation spectrum of MLL2 in a cohort of kabuki syndrome patients

BackgroundKabuki syndrome (Niikawa-Kuroki syndrome) is a rare, multiple congenital anomalies/mental retardation syndrome characterized by a peculiar face, short stature, skeletal, visceral and dermatoglyphic abnormalities, cardiac anomalies, and immunological defects. Recently mutations in the histone methyl transferase MLL2 gene have been identified as its underlying cause.MethodsGenomic DNAs were extracted from 62 index patients clinically diagnosed as affected by Kabuki syndrome. Sanger sequencing was performed to analyze the whole coding region of the MLL2 gene including intron-exon junctions. The putative causal and possible functional effect of each nucleotide variant identified was estimated by in silico prediction tools.ResultsWe identified 45 patients with MLL2 nucleotide variants. 38 out of the 42 variants were never described before. Consistently with previous reports, the majority are nonsense or frameshift mutations predicted to generate a truncated polypeptide. We also identified 3 indel, 7 missense and 3 splice site.ConclusionsThis study emphasizes the relevance of mutational screening of the MLL2 gene among patients diagnosed with Kabuki syndrome. The identification of a large spectrum of MLL2 mutations possibly offers the opportunity to improve the actual knowledge on the clinical basis of this multiple congenital anomalies/mental retardation syndrome, design functional studies to understand the molecular mechanisms underlying this disease, establish genotype-phenotype correlations and improve clinical management.

7q11.23 dosage-dependent dysregulation in human pluripotent stem cells affects transcriptional programs in disease-relevant lineages

Cell reprogramming promises to make characterization of the impact of human genetic variation on health and disease experimentally tractable by enabling the bridging of genotypes to phenotypes in developmentally relevant human cell lineages. Here we apply this paradigm to two disorders caused by symmetrical copy number variations of 7q11.23, which display a striking combination of shared and symmetrically opposite phenotypes—Williams-Beuren syndrome and 7q-microduplication syndrome. Through analysis of transgene-free patient-derived induced pluripotent stem cells and their differentiated derivatives, we find that 7q11.23 dosage imbalance disrupts transcriptional circuits in disease-relevant pathways beginning in the pluripotent state. These alterations are then selectively amplified upon differentiation of the pluripotent cells into disease-relevant lineages. A considerable proportion of this transcriptional dysregulation is specifically caused by dosage imbalances in GTF2I, which encodes a key transcription factor at 7q11.23 that is associated with the LSD1 repressive chromatin complex and silences its dosage-sensitive targets.

Molecular Analysis, Pathogenic Mechanisms, and Readthrough Therapy on a Large Cohort of Kabuki Syndrome Patients

Kabuki syndrome (KS) is a multiple congenital anomalies syndrome characterized by characteristic facial features and varying degrees of mental retardation, caused by mutations in KMT2D/MLL2 and KDM6A/UTX genes. In this study, we performed a mutational screening on 303 Kabuki patients by direct sequencing, MLPA, and quantitative PCR identifying 133 KMT2D, 62 never described before, and four KDM6A mutations, three of them are novel. We found that a number of KMT2D truncating mutations result in mRNA degradation through the nonsense‐mediated mRNA decay, contributing to protein haploinsufficiency. Furthermore, we demonstrated that the reduction of KMT2D protein level in patients’ lymphoblastoid and skin fibroblast cell lines carrying KMT2D‐truncating mutations affects the expression levels of known KMT2D target genes. Finally, we hypothesized that the KS patients may benefit from a readthrough therapy to restore physiological levels of KMT2D and KDM6A proteins. To assess this, we performed a proof‐of‐principle study on 14 KMT2D and two KDM6A nonsense mutations using specific compounds that mediate translational readthrough and thereby stimulate the re‐expression of full‐length functional proteins. Our experimental data showed that both KMT2D and KDM6A nonsense mutations displayed high levels of readthrough in response to gentamicin treatment, paving the way to further studies aimed at eventually treating some Kabuki patients with readthrough inducers.

2p15-p16.1 microdeletions encompassing and proximal to BCL11A are associated with elevated HbF in addition to neurologic impairment

Elevated fetal hemoglobin (HbF) ameliorates the clinical severity of hemoglobinopathies such as β-thalassemia and sickle cell anemia. Currently, the only curative approach for individuals under chronic transfusion/chelation support therapy is allogeneic stem cell transplantation. However, recent analyses of heritable variations in HbF levels have provided a new therapeutic target for HbF reactivation: the transcriptional repressor BCL11A. Erythroid-specific BCL11A abrogation is now actively being sought as a therapeutic avenue, but the specific impact of such disruption in humans remains to be determined. Although single nucleotide polymorphisms in BCL11A erythroid regulatory elements have been reported, coding mutations are scarcer. It is thus of great interest that patients have recently been described with microdeletions encompassing BCL11A. These patients display neurodevelopmental abnormalities, but whether they show increased HbF has not been reported. We have examined the hematological phenotype, HbF levels, and erythroid BCL11A expression in 3 such patients. Haploinsufficiency of BCL11A induces only partial developmental γ-globin silencing. Of greater interest is that a patient with a downstream deletion exhibits reduced BCL11A expression and increased HbF. Novel erythroid-specific regulatory elements in this region may be required for normal erythroid BCL11A expression, whereas loss of separate elements in the developing brain may explain the neurological phenotype.

2q31.2q32.3 Deletion Syndrome : Report of an Adult Patient

A 36‐year‐old patient with a disorder characterized by severe mental retardation, behavioral problems, dysmorphic face, “muscular build,” and hand/foot anomalies, is reported. Following a diagnosis of de novo pericentric inversion of chromosome 8 based on standard cytogenetic analysis, a subsequent 75 kb array‐CGH investigation disclosed a deletion spanning for about 13.7 Mb in the 2q31.2q32.3 region. Whole painting of chromosome 8 established the intrachromosomal nature of the rearrangement and FISH analysis with locus‐specific probes confirmed the deletion on the long arm of chromosome 2. The deleted region, clinical outcome, and medical history in this patient are mainly superimposable to those reported in a published 8‐year‐old boy, suggesting that this genomic segment is prone to rearrangements and its hemizygosity gives rise to a clinically recognizable syndrome. The role of some genes mapping in the deleted region and related with distinct disorders is discussed. Interestingly, deletion of MSTN gene, a negative regulator of muscle growth, was associated in our patient with a “muscular build,” a feature which could be regarded as a handle for clinical recognition of this syndrome.

Deletion 2p15-16.1 syndrome: case report and review.

We report on a 9‐year‐old female patient with facial anomalies and developmental delay, heterozygous for three de novo rearrangements: a paracentric inversion of chromosome 7, an apparently balanced translocation between chromosome 1 and 7, involving the same inverted chromosome 7, detected by standard cytogenetic analysis [46,XX, der(7) inv(7)(q21.1q32.1)t(1;7)(q23q32.1)]; and a 2p16.1 deletion, spanning about 3.5 Mb of genomic DNA, shown by SNP‐array analysis [arr 2p16.1 (56,706,666–60,234,485)x1 dn]. Clinical features and cytogenetic imbalance in our patient were similar to those reported in five published cases, suggesting that this genomic region is prone to recombination and its hemizygosity results in a distinct although variable spectrum of clinical manifestations.

Absence of deletion and duplication of MLL2 and KDM6A genes in a large cohort of patients with Kabuki syndrome

Kabuki syndrome is a rare, multiple congenital anomaly/mental retardation syndrome caused by MLL2 point mutations and KDM6A microdeletions. We screened a large cohort of MLL2 mutation-negative patients for MLL2 and KDM6A exon(s) microdeletion and microduplication. Our assays failed to detect such rearrangements in MLL2 as well as in KDM6A gene. These results show that these genomic events are extremely rare in the Kabuki syndrome, substantiating its genetic heterogeneity and the search for additional causative gene(s).

A New Homozygous IGF1R Variant Defines a Clinically Recognizable Incomplete Dominant form of SHORT Syndrome

Here, we describe a child, born from consanguineous parents, with clinical features of SHORT syndrome, high IGF1 levels, developmental delay, CNS defects, and marked progeroid appearance. By exome sequencing, we identified a new homozygous c.2201G>T missense mutation in the IGF1R gene. Probands parents and other relatives, all heterozygous carriers of the mutation, presented with milder phenotype including high IGFI levels, short stature, and type 2 diabetes. Functional studies using patients cell lines showed a lower IGF1R expression that leads to the alteration of IGF1R‐mediated PI3K/AKT/mTOR downstream pathways, including autophagy. This study defines a clinically recognizable incomplete dominant form of SHORT syndrome, and provides relevant insights into the pathophysiological and phenotypical consequences of IGF1R mutations.

Familial occurrence of multiple pterygium syndrome: Expression in a heterozygote of the recessive form or variability of the dominant form?

We report on a case with apparently familial multiple pterygium syndrome (MPS). The proposita was a 3‐year‐old girl with classical symptoms of MPS. A careful clinical examination of the father disclosed the presence of few minor signs of the syndrome, including difficulty in opening the mouth widely, scoliosis, pectus excavatum, hands with slight cutaneous syndactyly, and bilateral single palmar creases. The radiograph of the hands disclosed malformed carpal bones and an altered metacarpal‐phalangeal pattern. The father shows limited symptoms, which has been reported before in the autosomal dominant form of MPS. However, it is also possible that he is showing a heterozygous state of the autosomal recessive form of MPS. In conclusion, we emphasize the importance of examining accurately the parents of a child who has classical MPS phenotype, even those with normal stature and an absence of facial anomalies.

Stem cells from human amniotic fluid exert immunoregulatory function via secreted indoleamine 2,3-dioxygenase1

Although human amniotic fluid does contain different populations of foetal‐derived stem cells, scanty information is available on the stemness and the potential immunomodulatory activity of in vitro expanded, amniotic fluid stem cells. By means of a methodology unrequiring immune selection, we isolated and characterized different stem cell types from second‐trimester human amniotic fluid samples (human amniotic fluid stem cells, HASCs). Of those populations, one was characterized by a fast doubling time, and cells were thus designated as fHASCs. Cells maintained their original phenotype under prolonged in vitro passaging, and they were able to originate embryoid bodies. Moreover, fHASCs exhibited regulatory properties when treated with interferon (IFN)‐γ, including induction of the immunomodulatory enzyme indoleamine 2,3‐dioxygenase 1 (IDO1). On coculture with human peripheral blood mononuclear cells, IFN‐γ–treated fHASCs caused significantly decreased T‐cell proliferation and increased frequency in CD4+ CD25+ FOXP3+ regulatory T cells. Both effects required an intact IDO1 function and were cell contact‐independent. An unprecedented finding in our study was that purified vesicles from IFN‐γ–treated fHASCs abundantly expressed the functional IDO1 protein, and those vesicles were endowed with an fHASC‐like regulatory function. In vivo, fHASCs were capable of immunoregulatory function, promoting allograft survival in a mouse model of allogeneic skin transplantation. This was concurrent with the expansion of CD4+ CD25+ Foxp3+ T cells in graft‐draining lymph nodes from recipient mice. Thus fHASCs, or vesicles thereof, may represent a novel opportunity for immunoregulatory maneuvers both in vitro and in vivo.