Spectrum of MLL2 (ALR) mutations in 110 cases of Kabuki syndrome

The H3K27me3 demethylase UTX in normal development and disease

In 2007, the Ubiquitously Transcribed Tetratricopeptide Repeat on chromosome X (UTX) was identified as a histone demethylase that specifically targets di- and tri-methyl groups on lysine 27 of histone H3 (H3K27me2/3). Since then, UTX has been proven essential during normal development, as it is critically required for correct reprogramming, embryonic development and tissue-specific differentiation. UTX is a member of the MLL2 H3K4 methyltransferase complex and its catalytic activity has been linked to regulation of HOX and RB transcriptional networks. In addition, an H3K27me2/3 demethylase independent function for UTX was uncovered in promoting general chromatin remodeling in concert with the BRG1-containing SWI/SNF remodeling complex. Constitutional inactivation of UTX causes a specific hereditary disorder called the Kabuki syndrome, whereas somatic loss of UTX has been reported in a variety of human cancers. Here, we compile the breakthrough discoveries made from the first disclosure of UTX as a histone demethylase till the identification of disease-related UTX mutations and specific UTX inhibitors.

Bronchial isomerism in a Kabuki syndrome patient with a novel mutation in MLL2 gene

Background

Kabuki syndrome (KS) is a rare, multiple congenital anomalies/intellectual disability syndrome caused by mutations of MLL2 gene, which codifies for a histone methyltrasferase that regulates the embryogenesis and the tissue development. Left-bronchial isomerism is a rare congenital abnormality that can be defined as the absence of the normal lateralizing features which distinguish right and left-sides in the lungs. To date, this is the first report of left-bronchial isomerism in association with KS.

Case presentation

A one-month-old Caucasian male patient underwent our attention for microcephaly, dysmorphic features (long palpebral fissures, eyebrows with sparse lateral third, everted lower eyelids, blue sclerae, large dysplastic ears, lower lip pits), persistent fetal fingertip pads, short stature, heart defects (interventricular defect and aortic coarctation), unilateral cryptorchidism, hypotonia and delay in gross motor skills. These features suggested a diagnosis of KS and a molecular analysis confirmed a novel frame-shift mutation in the exon 11 of MLL2 gene. Subsequently, given recurrent respiratory infections with a normal immunological status, he underwent a chest CT scan that showed a left bronchial isomerism.

Conclusion

We report a patient affected by KS, with a novel MLL2 mutation and an atypical phenotype characterized by left-side bronchial isomerism. Interestingly, genes involved in the heterotaxia/isomerism such as ROCK2 and SHROOM3 are known to interact with MLL2 gene. In order to achieve a correct diagnosis and an appropriate therapy, the presence of pulmonary anatomical variations should be investigated in KS patients with respiratory signs not associated to immunological deficiency. Finally, our findings support the hypothesis that the mutations leading to a complete loss of function of MLL2 gene is often associated with complex visceral malformations.

An individual with blepharophimosis-ptosis-epicanthus inversus syndrome (BPES) and additional features expands the phenotype associated with mutations in KAT6B

Blepharophimosis-ptosis-epicanthus inversus syndrome (BPES) is an autosomal dominant disorder caused by mutations in FOXL2. We identified an individual with BPES and additional phenotypic features who did not have a FOXL2 mutation. We used whole exome sequencing to identify a de novo mutation in KAT6B (lysine acetyltransferase 6B) in this individual. The mutation was a 2-bp insertion leading to a frameshift which resulted in a premature stop codon. The resulting truncated protein does not have the C-terminal serine/methionine transcription activation domain necessary for interaction with other transcriptional and epigenetic regulators. This mutation likely has a dominant-negative or gain-of-function effect, similar to those observed in other genetic disorders resulting from KAT6B mutations, including Say-Barber-Biesecker-Young-Simpson (SBBYSS) and genitopatellar syndrome (GTPTS). Thus, our subject's phenotype broadens the spectrum of clinical findings associated with mutations in KAT6B. Furthermore, our results suggest that individuals with BPES without a FOXL2 mutation should be tested for KAT6B mutations. The transcriptional and epigenetic regulation mediated by KAT6B appears crucial to early developmental processes, which when perturbed can lead to a wide spectrum of phenotypic outcomes.

Translating personalized medicine using new genetic technologies in clinical practice: the ethical issues

The integration of new genetic technologies into clinical practice holds great promise for the personalization of medical care, particularly the use of large-scale DNA sequencing for genome-wide genetic testing. However, these technologies also yield unprecedented amounts of information whose clinical implications are not fully understood, and we are still developing technical standards for measuring sequence accuracy. These technical and clinical challenges raise ethical issues that are similar to but qualitatively different from those that we are accustomed to dealing with for traditional medical genetics. The sheer amount of information afforded by genome sequencing requires rethinking of how to implement core ethical principles including, but not limited to: informed consent, privacy and data ownership and sharing, technology regulation, issues of access, particularly as new technology is integrated into clinical practice, and issues of potential stigma and impact on perceptions of disability. In this article, we will review the issues of informed consent, privacy, data ownership and technology regulation as they relate to the emerging field of personalized medicine and genomics.

Hypoglycemia in Kabuki syndrome

Kabuki syndrome (KS) is a congenital malformation disorder with a spectrum of clinical manifestations involving different organs. Until the identification of MLL2 gene mutation in 2010, the diagnosis was made only clinically by the characteristic facial features with other common and uncommon features. Hypoglycemia, although an uncommon feature in KS, is very important to be recognized, as early diagnosis and appropriate management will reduce further long-term neurologic morbidity in these patients. We report on four patients with KS presenting with persistent hypoglycemia. Hyperinsulinemic hypoglycemia was the cause of hypoglycemia in two out of four patients and one patient had growth hormone deficiency. The mechanism of the hypoglycemia in one patient is still unclear. Three out of these four patients were found to have mutation in the MLL2 gene. Our observations suggest that patients with KS may have hypoglycemia due to different mechanisms and that MLL2 gene may have a role in glucose physiology.

Automethylation activities within the mixed lineage leukemia-1 (MLL1) core complex reveal evidence supporting a "two-active site" model for multiple histone H3 lysine 4 methylation

The mixed lineage leukemia-1 (MLL1) core complex predominantly catalyzes mono- and dimethylation of histone H3 at lysine 4 (H3K4) and is frequently altered in aggressive acute leukemias. The molecular mechanisms that account for conversion of mono- to dimethyl H3K4 (H3K4me1,2) are not well understood. In this investigation, we report that the suppressor of variegation, enhancer of zeste, trithorax (SET) domains from human MLL1 and Drosophila Trithorax undergo robust intramolecular automethylation reactions at an evolutionarily conserved cysteine residue in the active site, which is inhibited by unmodified histone H3. The location of the automethylation in the SET-I subdomain indicates that the MLL1 SET domain possesses significantly more conformational plasticity in solution than suggested by its crystal structure. We also report that MLL1 methylates Ash2L in the absence of histone H3, but only when assembled within a complex with WDR5 and RbBP5, suggesting a restraint for the architectural arrangement of subunits within the complex. Using MLL1 and Ash2L automethylation reactions as probes for histone binding, we observed that both automethylation reactions are significantly inhibited by stoichiometric amounts of unmethylated histone H3, but not by histones previously mono-, di-, or trimethylated at H3K4. These results suggest that the H3K4me1 intermediate does not significantly bind to the MLL1 SET domain during the dimethylation reaction. Consistent with this hypothesis, we demonstrate that the MLL1 core complex assembled with a catalytically inactive SET domain variant preferentially catalyzes H3K4 dimethylation using the H3K4me1 substrate. Taken together, these results are consistent with a “two-active site” model for multiple H3K4 methylation by the MLL1 core complex.

Lower lip pits: van der woude or kabuki syndrome?

Kabuki syndrome (KS) is a multiple congenital anomaly/mental retardation syndrome with characteristic facial features. Despite more than 350 documented cases and recent correlation of MLL2 mutations as a genetic cause, its full clinical spectrum is still being defined. This report describes two patients who were initially diagnosed with Van der Woude syndrome (VWS) based on the presence of lower lip pits. However, this finding can occur with KS, albeit infrequently. For patients with lower lip pits, a thorough evaluation should be made to distinguish between VWS and KS, as there are differences in long-term prognosis.

Clinical and molecular spectrum of renal malformations in Kabuki syndrome

OBJECTIVE

To determine the frequency and types of renal malformations, and to evaluate renal function in a cohort of patients with Kabuki syndrome (KS).

STUDY DESIGN

Renal ultrasound scans and plasma creatinine measurements were collected from a French cohort of 94 patients with genotyped KS. Renal function was evaluated based on the estimated glomerular filtration rate. A genotype-phenotype study was conducted for renal and urinary tract malformations.

RESULTS

Renal malformations were present in 22% of cases, and urinary tract anomalies were present in 15%. Renal malformations were observed in 28% of the MLL2 mutation-positive group and in 0% of the MLL2 mutation-negative group (P = .015). No correlation was found between the presence or absence of renal or urinary tract malformations and the location or type of MLL2 mutation. Renal function was normal except for 1 patient with a MLL2 mutation diagnosed in the first days of life and severe renal disease due to unilateral renal agenesia and controlateral severe hypoplasia that progressed to the terminal stage at age 2 years.

CONCLUSION

Our study emphasizes the need for ultrasound and renal function screening in children diagnosed with KS.

A novel MLL2 gene mutation in a Korean patient with Kabuki syndrome

Kabuki syndrome (KS) is a rare genetic disease with a distinctive dysmorphic face, intellectual disability, and multiple congenital abnormalities. KS is inherited in an autosomal dominant manner. As the primary cause of KS, MLL2 mutations have been identified in 56-76% of affected individuals who have been tested, suggesting that there may be additional genes associated with KS. Recently, a few KS individuals have been found to have de novo partial or complete deletions of an X chromosome gene, KDM6A, which encodes a histone demethylase that interacts with MLL2. Nevertheless, mutations in MLL2 are the major cause of KS. Although there are a few reports of KS patients in Korea, none of these had been confirmed by genetic analysis. Here, we report a case of a Korean patient with clinical features of KS. Using direct sequencing, we identified a frameshift heterozygous mutation for MLL2: (c.5256_5257delGA;p.Lys1753Alafs*34). Clinically, the patient presented with typical facial features, and diagnosis of KS was based on the diagnostic criteria. While KS is a rare disease, other malformations that overlap with those found in individuals with KS are common. Hence, the diagnosis of KS by mutational analysis can be a valuable method for patients with KS-like syndromes. Furthermore, in the near future, other genes could be identified in patients with KS without a detectable MLL2 mutation.

Of mice and men: molecular genetics of congenital heart disease

Congenital heart disease (CHD) affects nearly 1 % of the population. It is a complex disease, which may be caused by multiple genetic and environmental factors. Studies in human genetics have led to the identification of more than 50 human genes, involved in isolated CHD or genetic syndromes, where CHD is part of the phenotype. Furthermore, mapping of genomic copy number variants and exome sequencing of CHD patients have led to the identification of a large number of candidate disease genes. Experiments in animal models, particularly in mice, have been used to verify human disease genes and to gain further insight into the molecular pathology behind CHD. The picture emerging from these studies suggest that genetic lesions associated with CHD affect a broad range of cellular signaling components, from ligands and receptors, across down-stream effector molecules to transcription factors and co-factors, including chromatin modifiers.

MLL2 and KDM6A mutations in patients with Kabuki syndrome

Kabuki syndrome is a congenital anomaly syndrome characterized by developmental delay, intellectual disability, specific facial features including long palpebral fissures and ectropion of the lateral third of the lower eyelids, prominent digit pads, and skeletal and visceral abnormalities. Mutations in MLL2 and KDM6A cause Kabuki syndrome. We screened 81 individuals with Kabuki syndrome for mutations in these genes by conventional methods (n = 58) and/or targeted resequencing (n = 45) or whole exome sequencing (n = 5). We identified a mutation in MLL2 or KDM6A in 50 (61.7%) and 5 (6.2%) cases, respectively. Thirty-five MLL2 mutations and two KDM6A mutations were novel. Non-protein truncating-type MLL2 mutations were mainly located around functional domains, while truncating-type mutations were scattered through the entire coding region. The facial features of patients in the MLL2 truncating-type mutation group were typical based on those of the 10 originally reported patients with Kabuki syndrome; those of the other groups were less typical. High arched eyebrows, short fifth finger, and hypotonia in infancy were more frequent in the MLL2 mutation group than in the KDM6A mutation group. Short stature and postnatal growth retardation were observed in all individuals with KDM6A mutations, but in only half of the group with MLL2 mutations.

Transcriptome analyses of the human retina identify unprecedented transcript diversity and 3.5 Mb of novel transcribed sequence via significant alternative splicing and novel genes

BACKGROUND

The retina is a complex tissue comprised of multiple cell types that is affected by a diverse set of diseases that are important causes of vision loss. Characterizing the transcripts, both annotated and novel, that are expressed in a given tissue has become vital for understanding the mechanisms underlying the pathology of disease.

RESULTS

We sequenced RNA prepared from three normal human retinas and characterized the retinal transcriptome at an unprecedented level due to the increased depth of sampling provided by the RNA-seq approach. We used a non-redundant reference transcriptome from all of the empirically-determined human reference tracks to identify annotated and novel sequences expressed in the retina. We detected 79,915 novel alternative splicing events, including 29,887 novel exons, 21,757 3' and 5' alternate splice sites, and 28,271 exon skipping events. We also identified 116 potential novel genes. These data represent a significant addition to the annotated human transcriptome. For example, the novel exons detected increase the number of identified exons by 3%. Using a high-throughput RNA capture approach to validate 14,696 of these novel transcriptome features we found that 99% of the putative novel events can be reproducibly detected. Further, 15-36% of the novel splicing events maintain an open reading frame, suggesting they produce novel protein products.

CONCLUSIONS

To our knowledge, this is the first application of RNA capture to perform large-scale validation of novel transcriptome features. In total, these analyses provide extensive detail about a previously uncharacterized level of transcript diversity in the human retina.

Hypothalamic pituitary complications in Kabuki syndrome

Kabuki syndrome is characterized by distinctive facial features, multiple anomalies and mental retardation. In this syndrome, structural CNS abnormalities are commonly observed, but congenital abnormalities in the pituitary gland or hypothalamus have rarely been reported. We searched the published medical literature on the complications in hypothalamic pituitary axis in this syndrome. As a result, only nine patients with Kabuki syndrome had been reported to have complications in hypothalamic pituitary axis in previous papers. Among the nine reported patients and one presented case in this report, GH deficiency was the most frequent complication and found in six patients. Precocious puberty and central diabetes insipidus (DI) was identified in two cases, respectively, and ACTH deficiency was found in one. One case had combination of GH deficiency and central DI. Three of the 10 patients demonstrated abnormal pituitary findings in MRI study. Two of the six patients with GH deficiency were accompanied with premature thelarche. This review highlights that patients with Kabuki syndrome could present various clinical manifestations due to abnormalities in hypothalamic pituitary axis.

From neural development to cognition: unexpected roles for chromatin

Recent genome-sequencing studies in human neurodevelopmental and psychiatric disorders have uncovered mutations in many chromatin regulators. These human genetic studies, along with studies in model organisms, are providing insight into chromatin regulatory mechanisms in neural development and how alterations to these mechanisms can cause cognitive deficits, such as intellectual disability. We discuss several implicated chromatin regulators, including BAF (also known as SWI/SNF) and CHD8 chromatin remodellers, HDAC4 and the Polycomb component EZH2. Interestingly, mutations in EZH2 and certain BAF complex components have roles in both neurodevelopmental disorders and cancer, and overlapping point mutations are suggesting functionally important residues and domains. We speculate on the contribution of these similar mutations to disparate disorders.

Multiple pilomatricomas in Kabuki syndrome

Pilomatricoma is a benign tumor of the hair matrix cell that presents predominantly in childhood. Although pilomatricoma occurs spontaneously, multiple pilomatricomas have been described in association with several inherited syndromes. We report on a 28-year-old man with Kabuki syndrome with three pilomatricomas in his head and thigh. Although several reports describe multiple pilomatricomas associated with Turner syndrome, there are no reports of multiple pilomatricomas combined with Kabuki syndrome. Ectodermal abnormalities such as hair abnormality and hirsutism are symptoms of Kabuki syndrome, and pilomatricomas are frequently associated with the mutations of beta-catenin in hair follicle development. The predisposition of pilomatricomas may be not merely a coincidental finding, but an added association with Kabuki syndrome.

Trans-tail regulation of MLL4-catalyzed H3K4 methylation by H4R3 symmetric dimethylation is mediated by a tandem PHD of MLL4

Mixed-lineage leukemia 4 (MLL4; also called MLL2 and ALR) enzymatically generates trimethylated histone H3 Lys 4 (H3K4me3), a hallmark of gene activation. However, how MLL4-deposited H3K4me3 interplays with other histone marks in epigenetic processes remains largely unknown. Here, we show that MLL4 plays an essential role in differentiating NT2/D1 stem cells by activating differentiation-specific genes. A tandem plant homeodomain (PHD(4-6)) of MLL4 recognizes unmethylated or asymmetrically dimethylated histone H4 Arg 3 (H4R3me0 or H4R3me2a) and is required for MLL4's nucleosomal methyltransferase activity and MLL4-mediated differentiation. Kabuki syndrome mutations in PHD(4-6) reduce PHD(4-6)'s binding ability and MLL4's catalytic activity. PHD(4-6)'s binding strength is inhibited by H4R3 symmetric dimethylation (H4R3me2s), a gene-repressive mark. The protein arginine methyltransferase 7 (PRMT7), but not PRMT5, represses MLL4 target genes by up-regulating H4R3me2s levels and antagonizes MLL4-mediated differentiation. Consistently, PRMT7 knockdown increases MLL4-catalyzed H3K4me3 levels. During differentiation, decreased H4R3me2s levels are associated with increased H3K4me3 levels at a cohort of genes, including many HOXA and HOXB genes. These findings indicate that the trans-tail inhibition of MLL4-generated H3K4me3 by PRMT7-regulated H4R3me2s may result from H4R3me2s's interference with PHD(4-6)'s binding activity and is a novel epigenetic mechanism that underlies opposing effects of MLL4 and PRMT7 on cellular differentiation.

A new paradigm emerges from the study of de novo mutations in the context of neurodevelopmental disease

The study of de novo point mutations (new germline mutations arising from the gametes of the parents) remained largely static until the arrival of next-generation sequencing technologies, which made both whole-exome sequencing (WES) and whole-genome sequencing (WGS) feasible in practical terms. Single nucleotide polymorphism genotyping arrays have been used to identify de novo copy-number variants in a number of common neurodevelopmental conditions such as schizophrenia and autism. By contrast, as point mutations and microlesions occurring de novo are refractory to analysis by these microarray-based methods, little was known about either their frequency or impact upon neurodevelopmental disease, until the advent of WES. De novo point mutations have recently been implicated in schizophrenia, autism and mental retardation through the WES of case-parent trios. Taken together, these findings strengthen the hypothesis that the occurrence of de novo mutations could account for the high prevalence of such diseases that are associated with a marked reduction in fecundity. De novo point mutations are also known to be responsible for many sporadic cases of rare dominant mendelian disorders such as Kabuki syndrome, Schinzel-Giedion syndrome and Bohring-Opitz syndrome. These disorders share a common feature in that they are all characterized by intellectual disability. In summary, recent WES studies of neurodevelopmental and neuropsychiatric disease have provided new insights into the role of de novo mutations in these disorders. Our knowledge of de novo mutations is likely to be further accelerated by WGS. However, the collection of case-parent trios will be a prerequisite for such studies. This review aims to discuss recent developments in the study of de novo mutations made possible by technological advances in DNA sequencing.

Genetic syndromes caused by mutations in epigenetic genes

The orchestrated organization of epigenetic factors that control chromatin dynamism, including DNA methylation, histone marks, non-coding RNAs (ncRNAs) and chromatin-remodeling proteins, is essential for the proper function of tissue homeostasis, cell identity and development. Indeed, deregulation of epigenetic profiles has been described in several human pathologies, including complex diseases (such as cancer, cardiovascular and neurological diseases), metabolic pathologies (type 2 diabetes and obesity) and imprinting disorders. Over the last decade it has become increasingly clear that mutations of genes involved in epigenetic mechanism, such as DNA methyltransferases, methyl-binding domain proteins, histone deacetylases, histone methylases and members of the SWI/SNF family of chromatin remodelers are linked to human disorders, including Immunodeficiency Centromeric instability Facial syndrome 1, Rett syndrome, Rubinstein-Taybi syndrome, Sotos syndrome or alpha-thalassemia/mental retardation X-linked syndrome, among others. As new members of the epigenetic machinery are described, the number of human syndromes associated with epigenetic alterations increases. As recent examples, mutations of histone demethylases and members of the non-coding RNA machinery have recently been associated with Kabuki syndrome, Claes-Jensen X-linked mental retardation syndrome and Goiter syndrome. In this review, we describe the variety of germline mutations of epigenetic modifiers that are known to be associated with human disorders, and discuss the therapeutic potential of epigenetic drugs as palliative care strategies in the treatment of such disorders.

Haploinsufficiency of KDM6A is associated with severe psychomotor retardation, global growth restriction, seizures and cleft palate

We describe a female subject (DGAP100) with a 46,X,t(X;5)(p11.3;q35.3)inv(5)(q35.3q35.1)dn, severe psychomotor retardation with hypotonia, global postnatal growth restriction, microcephaly, globally reduced cerebral volume, seizures, facial dysmorphia and cleft palate. Fluorescence in situ hybridization and whole-genome sequencing demonstrated that the X chromosome breakpoint disrupts KDM6A in the second intron. No genes were directly disrupted on chromosome 5. KDM6A is a histone 3 lysine 27 demethylase and a histone 3 lysine 4 methyltransferase. Expression of KDM6A is significantly reduced in DGAP100 lymphoblastoid cells compared to control samples. We identified nine additional cases with neurodevelopmental delay and various other features consistent with the DGAP100 phenotype with copy number variation encompassing KDM6A from microarray databases. We evaluated haploinsufficiency of kdm6a in a zebrafish model. kdm6a is expressed in the pharyngeal arches and ethmoid plate of the developing zebrafish, while a kdm6a morpholino knockdown exhibited craniofacial defects. We conclude KDM6A dosage regulation is associated with severe and diverse structural defects and developmental abnormalities.

Unmasking Kabuki syndrome

The identification of de novo dominant mutations in KMT2D (MLL2) as the main cause of Kabuki syndrome (KS) has shed new light on the pathogenesis of this well-delineated condition consisting of a peculiar facial appearance, short stature, organ malformations and a varying degree of intellectual disability. Mutation screening studies have confirmed KMT2D as the major causative gene for KS and have at the same time provided evidence for its genetic heterogeneity. In this review, we aim to summarize the current clinical and molecular genetic knowledge on KS, provide genotype-phenotype correlations and propose a strategic clinical and molecular diagnostic approach for patients with suspected KS.

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).

MLL2 mosaic mutations and intragenic deletion-duplications in patients with Kabuki syndrome

Kabuki syndrome (KS) is a rare multi-system disorder that can result in a variety of congenital malformations, typical dysmorphism and variable learning disability. It is caused by MLL2 point mutations in the majority of the cases and, rarely by deletions involving KDM6A. Nearly one third of cases remain unsolved. Here, we expand the known genetic basis of KS by presenting five typical patients with the condition, all of whom have novel MLL2 mutation types- two patients with mosaic small deletions, one with a mosaic whole-gene deletion, one with a multi-exon deletion and one with an intragenic multi-exon duplication. We recommend MLL2 dosage studies for all patients with typical KS, where traditional Sanger sequencing fails to identify mutations. The prevalence of such MLL2 mutations in KS may be comparable with deletions involving KDM6A. These findings may be helpful in understanding the mutational mechanism of MLL2 and the disease mechanism of KS.

Infrequent Manifestations of Kabuki Syndrome in a Patient with Novel MLL2 Mutation

We present a case of a 9-month-old Hispanic female with Kabuki syndrome with some infrequent manifestations including a single umbilical artery, butterfly vertebrae, a small larynx, a preauricular pit, microtia with internal ear abnormalities, abnormal calcium metabolism, premature thelarche, neonatal/persistent hypoglycemia and eventration of the diaphragm. She was found to have a previously unreported nonsense MLL2 mutation. This is the first case that includes all such findings occurring simultaneously that was genotyped.

Surgical treatment of hip dislocation in Kabuki syndrome: use of incomplete periacetabular osteotomy for posterior acetabular wall deficiency

PURPOSE

Kabuki syndrome is characterized by distinctive facial features, skeletal anomalies, persisting fingertip pads with dermatoglyphic abnormalities, postnatal growth deficiency and mental retardation. This report reviews our results in the operative treatment of hip dislocations in patients with Kabuki syndrome.

METHODS

Between 2001 and 2009, seven dislocated hips (three unilateral and two bilateral hips) in five patients (all girls) were operatively treated at our institution. The operative treatment consists of open reduction, femoral derotation varus osteotomy, pelvic osteotomy (Salter in one and incomplete periacetabular osteotomy in six hips) and capsular plication. The age of the patients at the time of surgery ranged from 2.4 to 5.7 years, with an average of 3.6 years.

RESULTS

The follow-up postoperative period ranged from 3.2 to 6.3 years, with an average of 5.0 years. At the final follow-up, all patients reported no click and no pain, and showed well-contained hips by radiographs. All seven hips were graded as Severin class I-II. One patient presented as having habitual dislocation of the hip 4.4 years after surgery. Computed tomographic (CT) scans revealed posterior acetabular wall deficiency, which was not corrected by the anterolaterally directed Salter osteotomy. The incomplete periacetabular osteotomy provided sufficient posterolateral coverage of the acetabulum.

CONCLUSION

Operative treatment combining open reduction, femoral derotation varus and incomplete periacetabular osteotomies, and capsular plication provided successful results in patients with Kabuki syndrome who had the characteristics of hip instability such as ligamentous laxity, muscular hypotonia and posterior acetabular wall deficiency.

Identifying disease mutations in genomic medicine settings: current challenges and how to accelerate progress

The pace of exome and genome sequencing is accelerating, with the identification of many new disease-causing mutations in research settings, and it is likely that whole exome or genome sequencing could have a major impact in the clinical arena in the relatively near future. However, the human genomics community is currently facing several challenges, including phenotyping, sample collection, sequencing strategies, bioinformatics analysis, biological validation of variant function, clinical interpretation and validity of variant data, and delivery of genomic information to various constituents. Here we review these challenges and summarize the bottlenecks for the clinical application of exome and genome sequencing, and we discuss ways for moving the field forward. In particular, we urge the need for clinical-grade sample collection, high-quality sequencing data acquisition, digitalized phenotyping, rigorous generation of variant calls, and comprehensive functional annotation of variants. Additionally, we suggest that a 'networking of science' model that encourages much more collaboration and online sharing of medical history, genomic data and biological knowledge, including among research participants and consumers/patients, will help establish causation and penetrance for disease causal variants and genes. As we enter this new era of genomic medicine, we envision that consumer-driven and consumer-oriented efforts will take center stage, thus allowing insights from the human genome project to translate directly back into individualized medicine.

Mirror-image asymmetry in monozygotic twins with kabuki syndrome

Kabuki syndrome (OMIM 147920) is a rare disorder characterised by moderate intellectual disability, growth retardation, microcephaly and characteristic facial dysmorphic features which comprise long palpebral fissures, eversion of the lateral third of the eyelids and arched eyebrows with lateral sparseness. Mutations in MLL2 are the most frequent cause of this disorder. More than 100 MLL2 point mutations have been reported, but large intragenic deletions comprising one or more exons have not yet been identified. We report on a pair of monozygotic twin brothers in whom a deletion of 2 neighbouring exons was detected. The twins had the characteristic facial features of Kabuki syndrome, and they suffered from microcephaly, cleft lip and palate and congenital heart disease. Cleft lip and palate were left-sided in the first twin and right-sided in the second twin, i.e. they represented a mirror-image asymmetry. The intragenic deletion in these brothers broadens the spectrum of MLL2 mutations, and they provide a rare example of mirror-image asymmetry of congenital malformations in monozygotic twins.

Histone-modifying enzymes: regulators of developmental decisions and drivers of human disease

Precise transcriptional networks drive the orchestration and execution of complex developmental processes. Transcription factors possessing sequence-specific DNA binding properties activate or repress target genes in a step-wise manner to control most cell lineage decisions. This regulation often requires the interaction between transcription factors and subunits of massive protein complexes that bear enzymatic activities towards histones. The functional coupling of transcription proteins and histone modifiers underscores the importance of transcriptional regulation through chromatin modification in developmental cell fate decisions and in disease pathogenesis.

GRHL3/GET1 and trithorax group members collaborate to activate the epidermal progenitor differentiation program

The antagonistic actions of Polycomb and Trithorax are responsible for proper cell fate determination in mammalian tissues. In the epidermis, a self-renewing epithelium, previous work has shown that release from Polycomb repression only partially explains differentiation gene activation. We now show that Trithorax is also a key regulator of epidermal differentiation, not only through activation of genes repressed by Polycomb in progenitor cells, but also through activation of genes independent of regulation by Polycomb. The differentiation associated transcription factor GRHL3/GET1 recruits the ubiquitously expressed Trithorax complex to a subset of differentiation genes.

Human epidermal keratinocyte differentiation provides a highly suitable system to understand how progenitor cells become specialized. Previous work has implicated resolution of repressive histone modifications in the activation of the terminal differentiation gene expression program. Our work shows that this mechanism only accounts for the regulation of a subset of the differentiation gene expression program and that activating histone modifications by Trithorax chromatin modifiers, acting alone or in combination with the release from repressive chromatin changes, is essential. Furthermore, we show that the Trithorax complex is recruited to a subset of differentiation gene promoters by the transcription factor Grhl3, an evolutionarily conserved regulator of the epidermal differentiation program. Altered differentiation is characteristic for several skin diseases, including skin cancer and inflammatory diseases such as psoriasis. While genetic abnormalities play a role in these diseases, the cellular and macro-environment may also alter the course of these diseases through chromatin changes (epigenetics). Understanding the epigenetic regulation of keratinocyte differentiation may in the future lead to the development of new drugs for skin diseases.

Analysis of MLL2 gene in the first Brazilian family with Kabuki syndrome

Most patients with Kabuki syndrome (KS) are the only person in their family with the condition. However, familial cases of KS have been described showing evidence that this syndrome can be inherited as a dominant trait with variable expressivity. We report on two related individuals with facial findings characteristic of KS. The proposita had arched eyebrows, long and upward slanting palpebral fissures, cleft lip and palate, retromicrognathia, brachydactyly of hands and feet, stubby fingers, nail hypoplasia, and prominent finger pads. Her mother had eyebrows with dispersed lateral half, long and upward slanting palpebral fissures, retrognathia, abnormal and posteriorly rotated ears, prominent finger pads, brachydactyly of feet, learning difficulties, and psychomotor development delay. DNA sequencing revealed a novel missense mutation in the MLL2 gene in both the proposita and her mother. The mutation (p.R5432Q) was found in the exon 51, within the SET domain of the gene, which confers methyltransferase activity on the protein. Therefore, the epigenetic and transcriptional regulatory properties of this protein may be altered and this suggests that the mutation is the cause of phenotype observed in both the patient and her mother. The clinical signs and the molecular evidence in this family further support the notion that KS is an autosomal dominant condition with variable expressivity. To our knowledge this is the first report of a Brazilian family with recurrence of this syndrome.

New Genetic Insights into Congenital Heart Disease

There has been remarkable progress in understanding the genetic basis of cardiovascular malformations. Chromosome microarray analysis has provided a new tool to understand the genetic basis of syndromic cardiovascular malformations resulting from microdeletion or microduplication of genetic material, allowing the delineation of new syndromes. Improvements in sequencing technology have led to increasingly comprehensive testing for aortopathy, cardiomyopathy, single gene syndromic disorders, and Mendelian-inherited congenital heart disease. Understanding the genetic etiology for these disorders has improved their clinical recognition and management and led to new guidelines for treatment and family-based diagnosis and surveillance. These new discoveries have also expanded our understanding of the contribution of genetic variation, susceptibility alleles, and epigenetics to isolated congenital heart disease. This review summarizes the current understanding of the genetic basis of syndromic and non-syndromic congenital heart disease and highlights new diagnostic and management recommendations.

Deletion of KDM6A, a histone demethylase interacting with MLL2, in three patients with Kabuki syndrome

Kabuki syndrome (KS) is a rare genetic disease that causes developmental delay and congenital anomalies. Since the identification of MLL2 mutations as the primary cause of KS, such mutations have been identified in 56%-76% of affected individuals, suggesting that there may be additional genes associated with KS. Here, we describe three KS individuals with de novo partial or complete deletions of an X chromosome gene, KDM6A, that encodes a histone demethylase that interacts with MLL2. Although KDM6A escapes X inactivation, we found a skewed X inactivation pattern, in which the deleted X chromosome was inactivated in the majority of the cells. This study identifies KDM6A mutations as another cause of KS and highlights the growing role of histone methylases and histone demethylases in multiple-congenital-anomaly and intellectual-disability syndromes.

How genetically heterogeneous is Kabuki syndrome?: MLL2 testing in 116 patients, review and analyses of mutation and phenotypic spectrum

MLL2 mutations are detected in 55 to 80% of patients with Kabuki syndrome (KS). In 20 to 45% patients with KS, the genetic basis remains unknown, suggesting possible genetic heterogeneity. Here, we present the largest yet reported cohort of 116 patients with KS. We identified MLL2 variants in 74 patients, of which 47 are novel and a majority are truncating. We show that pathogenic missense mutations were commonly located in exon 48. We undertook a systematic facial KS morphology study of patients with KS at our regional dysmorphology meeting. Our data suggest that nearly all patients with typical KS facial features have pathogenic MLL2 mutations, although KS can be phenotypically variable. Furthermore, we show that MLL2 mutation-positive KS patients are more likely to have feeding problems, kidney anomalies, early breast bud development, joint dislocations and palatal malformations in comparison with MLL2 mutation-negative patients. Our work expands the mutation spectrum of MLL2 that may help in better understanding of this molecule, which is important in gene expression, epigenetic control of active chromatin states, embryonic development and cancer. Our analyses of the phenotype indicates that MLL2 mutation-positive and -negative patients differ systematically, and genetic heterogeneity of KS is not as extensive as previously suggested. Moreover, phenotypic variability of KS suggests that MLL2 testing should be considered even in atypical patients.