Wolf-Hirschhorn Syndrome Patients Research Articles

Wolf-Hirschhorn syndrome candidate 1 (Whsc1) methyltransferase signals via a Pitx2-miR-23/24 axis to effect tooth development

Wolf-Hirschhorn syndrome (WHS) is a developmental disorder attributed to a partial deletion on the short arm of chromosome 4. WHS patients suffer from oral manifestations including cleft lip and palate, hypodontia, and taurodontism. WHS candidate 1 (WHSC1) gene is a H3K36-specific methyltransferase that is deleted in every reported case of WHS. Mutation in this gene also results in tooth anomalies in patients. However, the correlation between genetic abnormalities and the tooth anomalies has remained controversial. In our study, we aimed to clarify the role of WHSC1 in tooth development. We profiled the Whsc1 expression pattern during mouse incisor and molar development by immunofluorescence staining and found Whsc1 expression is reduced as tooth development proceeds. Using real-time quantitative reverse transcription PCR, Western blot, chromatin immunoprecipitation, and luciferase assays, we determined that Whsc1 and Pitx2, the initial transcription factor involved in tooth development, positively and reciprocally regulate each other through their gene promoters. miRNAs are known to regulate gene expression posttranscriptionally during development. We previously reported miR-23a/b and miR-24-1/2 were highly expressed in the mature tooth germ. Interestingly, we demonstrate here that these two miRs directly target Whsc1 and repress its expression. Additionally, this miR cluster is also negatively regulated by Pitx2. We show the expression of these two miRs and Whsc1 are inversely correlated during mouse mandibular development. Taken together, our results provide new insights into the potential role of Whsc1 in regulating tooth development and a possible molecular mechanism underlying the dental defects in WHS.

The cation exchanger Letm1, circadian rhythms, and NAD(H) levels interconnect in diurnal zebrafish.

Mitochondria are fundamental for life and require balanced ion exchange to maintain proper functioning. The mitochondrial cation exchanger LETM1 sparks interest because of its pathophysiological role in seizures in the Wolf Hirschhorn Syndrome (WHS). Despite observation of sleep disorganization in epileptic WHS patients, and growing studies linking mitochondria and epilepsy to circadian rhythms, LETM1 has not been studied from the chronobiological perspective. Here we established a viable letm1 knock-out, using the diurnal vertebrate Danio rerio to study the metabolic and chronobiological consequences of letm1 deficiency. We report diurnal rhythms of Letm1 protein levels in wild-type fish. We show that mitochondrial nucleotide metabolism is deregulated in letm1-/- mutant fish, the rate-limiting enzyme of NAD+ production is up-regulated, while NAD+ and NADH pools are reduced. These changes were associated with increased expression amplitude of circadian core clock genes in letm1-/- compared with wild-type under light/dark conditions, suggesting decreased NAD(H) levels as a possible mechanism for circadian system perturbation in Letm1 deficiency. Replenishing NAD pool may ameliorate WHS-associated sleep and neurological disorders.

Distinct Epileptogenic Mechanisms Associated with Seizures in Wolf-Hirschhorn Syndrome.

Seizures are one of the clinical hallmarks of Wolf-Hirschhorn syndrome (WHS), causing a significant impact on the life quality, still in the first years of life. Even that the knowledge about WHS-related seizure candidate genes has grown, cumulative evidence suggests synergic haploinsufficiency of distinct genes within cellular networks that should be better elucidated. Herein, we evaluated common mechanisms between candidate genes from WHS seizure-susceptibility regions (SSR) and genes globally associated with epilepsy. For this purpose, data from 94 WHS patients delineated by chromosomal microarray analysis were integrated into a tissue-specific gene network with gene expression, drugs, and biological processes. We found functional modules and signaling pathways involving candidate and new genes with potential involvement in the WHS-related seizure phenotype. The proximity among the previous reported haploinsufficient candidate genes (PIGG, CPLX1, CTBP1, LETM1) and disease genes associated with epilepsy suggests not just one, but different impaired mechanisms in cellular networks responsible for the balance of neuronal activity in WHS patients, from which neuron communication is the most impaired in WHS-related seizures. Furthermore, CTBP1 obtained the largest number of drug associations, reinforcing its importance for adaptations of brain circuits and its putative use as a pharmacological target for treating seizures/epilepsy in patients with WHS.

The delineation of the Wolf-Hirschhorn syndrome over six decades: Illustration of the ongoing advances in phenotype analysis and cytogenomic technology.

Since Hirschhorn's description in 1961, the history and chronology of the clinical, cytogenetic, and molecular characterization of Wolf-Hirschhorn syndrome (WHS) elegantly demonstrates the remarkable advances in genetic technology over the last six decades that have paralleled the delineation of the phenotype. After mention in the Human Chromosome Newsletter of a child with a visible deletion of the top of a B chromosome group, 4-5, Hirschhorn and colleagues companioned their report with that of Wolf et al. in Humangenetik in 1965, and the condition was recognized and named. The 1960-1970s witnessed the description of many of the now classic chromosome disorders, including WHS, while HRB allowed for the recognition of chromosome syndromes with smaller deletions/duplications. FISH probes, developed in the next two decades, enabled the characterization of the critical region of WHS and improved clinical diagnosis with subtelomeric probes. Cytogenomic microarray in the early-mid 2000s led to both improved diagnosis of WHS patients and documentation of microdeletions of <5 megabases, helping to characterize the critical regions for specific component phenotypes (e.g., seizures, face). Recently exome sequencing technology has led to the discovery of WHS patients with WHSC1 loss of function variants, displaying some cardinal features of the phenotype (face, growth, and developmental delay).

Characterization of Wolf‐Hirschhorn Syndrome Candidate 1 ( Whsc1 ) in Pitx2 ‐ miR‐23/24 ‐mediated Tooth Development

Objective Wolf-Hirschhorn syndrome (WHS) is a developmental disorder attributed to a partial deletion on the short arm of chromosome 4. WHS patients suffer from oral manifestations including cleft lip and palate (CLP), hypodontia and taurodontism. However, the causative factors and underlying mechanisms of these oral anomalies are relatively unknown. Wolf-Hirschhorn syndrome candidate 1 (WHSC1) is a H3K36-specific methyltransferase that is frequently deleted in WHS. This gene has been associated with craniofacial defects including CLP and defects in occipital ossification. In our study, we aim to understand the role of WHSC1 in tooth development. Methods To characterize the role of Whsc1 in tooth development, we profiled the Whsc1 expression pattern during mouse tooth development by immunofluorescence staining (IF). To investigate the regulatory effects between Whsc1 and Pitx2, we overexpressed either Whsc1 or Pitx2 in oral epithelial cell line LS8 and detected their expression. Then, ChIP-PCR and luciferase assays were performed to confirm the binding on the promoter regions. To determine the negative regulation of Whsc1 by miR-23-3p and miR-24-3p, miRs were inhibited by our Plasmid-based microRNA inhibition system in PMIS-miR-23-27-24 embryos and LS8 cells followed by detecting the mRNA and protein level of Whsc1. Luciferase assays were also conducted to confirm the direct binding between miRs and Whsc1 3’UTR. Results Whsc1 expresses from early stage of tooth development and restricts to stem cell niches in homeostatic tooth germ. Whsc1 and Pitx2 reciprocally activate each other's expression through chromosomal and transcriptional regulation. miR-23-3p and miR-24-3p, two miRs that regulated by Pitx2, directly inhibit Whsc1. Conclusion Whsc1 expresses in the developing tooth germ and participates the Whsc1-Pitx2-miR23/24 regulatory network in oral epithelium cells. Our observations provide new insights into the potential role of Whsc1 in regulating tooth development and a possible causer of the dental defects in WHS.

The first familial NSD2 cases with a novel variant in a Chinese father and daughter with atypical WHS facial features and a 7.5-year follow-up of growth hormone therapy

BackgroundWolf-Hirschhorn syndrome is a well-characterized genomic disorder caused by 4p16.3 deletions. Wolf-Hirschhorn syndrome patients exhibit characteristic facial dysmorphism, growth retardation, developmental delay, intellectual disability and seizure disorders. Recently, NSD2 gene located within the 165 kb Wolf-Hirschhorn syndrome critical region was identified as the key causal gene responsible for most if not all phenotypes of Wolf-Hirschhorn syndrome. So far, eight NSD2 loss of function variants have been reported in patients from different parts of the world, all were de novo variants.MethodsIn our study, we performed whole exome sequencing for two patients from one family. We also reviewed more NSD2 mutation cases in pervious literature.ResultsA novel loss of function NSD2 variant, c.1577dupG (p.Asn527Lysfs*14), was identified in a Chinese family in the proband and her father both affected with intellectual disability. After reviewing more NSD2 mutation cases in pervious literature, we found none of them had facial features that can be recognized as Wolf-Hirschhorn syndrome. In addition, we have given our proband growth hormone and followed up with this family for 7.5 years.ConclusionsHere we reported the first familial NSD2 variant and the long-term effect of growth hormone therapy for patients. Our results suggested NSD2 mutation might cause a distinct intellectual disability and short stature syndrome.

Partial Monosomy 4p and Trisomy 12q due to a t(4;12)(p16.3;q24.31) Familial Translocation in Two Cousins

Wolf-Hirschhorn syndrome (WHS) is caused by a distal 4p monosomy usually involving the region of the WHSC1 and WHSC2 genes. About 40-45% of WHS patients show an unbalanced translocation leading to both 4p monosomy and partial trisomy of another chromosome arm. In this case report, we describe 2 female cousins (P1 and P2) with a derivative chromosome leading to a 4p16.3pter deletion and 12q24.31qter duplication. Conventional karyotyping and genomic analyses showed that they both had the same rearrangement derived from a balanced parental translocation involving chromosomes 4 and 12, t(4;12)(p16.3;q24.31). The rearrangements occurred between 4p16.3pter and 12q24.31qter detected by array-CGH analysis, with a 2.7-Mb loss at 4p and a large 12.4-Mb gain at 12q. Both affected patients shared global developmental delay and craniofacial dysmorphisms with some distinct phenotypic findings associated with both WHS and 12qter trisomy. P2 was more severely impaired than P1, and she showed severe intellectual disability, seizures, midface hypoplasia, unilateral microtia, and deafness which were absent in P1. Previous studies of distal 4p monosomies have found phenotypic variability in WHS which does not correlate with haploinsufficiency of specific genes. Features of 12q trisomies are diverse with developmental and growth delay, intellectual disability, behavioral problems, and facial abnormalities. Collectively, our analysis of the literature of 3 similar translocations involving 4p and 12q, together with the clinical features of the affected cousins in this familial translocation, permits an evaluation of genes closely linked to WHSC1 and WHSC2 in the context of WHS and the genes involved in 12q trisomy.

Molecular Mechanisms of Leucine Zipper EF-Hand Containing Transmembrane Protein-1 Function in Health and Disease.

Mitochondrial calcium (Ca2+) uptake shapes cytosolic Ca2+ signals involved in countless cellular processes and more directly regulates numerous mitochondrial functions including ATP production, autophagy and apoptosis. Given the intimate link to both life and death processes, it is imperative that mitochondria tightly regulate intramitochondrial Ca2+ levels with a high degree of precision. Among the Ca2+ handling tools of mitochondria, the leucine zipper EF-hand containing transmembrane protein-1 (LETM1) is a transporter protein localized to the inner mitochondrial membrane shown to constitute a Ca2+/H+ exchanger activity. The significance of LETM1 to mitochondrial Ca2+ regulation is evident from Wolf-Hirschhorn syndrome patients that harbor a haplodeficiency in LETM1 expression, leading to dysfunctional mitochondrial Ca2+ handling and from numerous types of cancer cells that show an upregulation of LETM1 expression. Despite the significance of LETM1 to cell physiology and pathophysiology, the molecular mechanisms of LETM1 function remain poorly defined. In this review, we aim to provide an overview of the current understanding of LETM1 structure and function and pinpoint the knowledge gaps that need to be filled in order to unravel the underlying mechanistic basis for LETM1 function.

Growth trajectory and pubertal tempo from birth till final height in a girl with Wolf-Hirschhorn syndrome.

SummaryGrowth anomaly is a prominent feature in Wolf-Hirschhorn syndrome (WHS), a rare congenital disorder caused by variable deletion of chromosome 4p. While growth charts have been developed for WHS patients 0–4 years of age and growth data available for Japanese WHS patients 0–17 years, information on pubertal growth and final height among WHS children remain lacking. Growth hormone (GH) therapy has been reported in two GH-sufficient children with WHS, allowing for pre-puberty catch up growth; however, pubertal growth and final height information was also unavailable. We describe the complete growth journey of a GH-sufficient girl with WHS from birth until final height (FH), in relation to her mid parental height (MPH) and target range (TR). Her growth trajectory and pubertal changes during childhood, when she was treated with growth hormone (GH) from 3 years 8 months old till 6 months post-menarche at age 11 years was fully detailed.Learning points:Pubertal growth characteristics and FH information in WHS is lacking.While pre-pubertal growth may be improved by GH, GH therapy may not translate to improvement in FH in WHS patients.Longitudinal growth, puberty and FH data of more WHS patients may improve the understanding of growth in its various phases (infancy/childhood/puberty).

A structured assessment of motor function, behavior, and communication in patients with Wolf–Hirschhorn syndrome

The present study aimed to increase the knowledge about Wolf–Hirschhorn syndrome (WHS), especially concerning motor function, autism spectrum disorders (ASD), and adapted behavior, but also regarding clinical symptoms in general. Motor function was evaluated via systematic observation. Standardized assessments such as the Vineland Adapted Behavior Scales II (VABS II), the Social Communication Questionnaire (SCQ), and the Child Behavior Checklist (CBCL) or Adult Behavior Checklist (ABCL) were used for the behavioral assessment. In total, two males and eight females between one and 48 years of age with a genetically confirmed diagnosis of WHS and their parents participated in this study. Deletion sizes were known for seven of the ten patients and varied between 55 Kb and 20 Mb. The chromosome coordinates were known for six of them, and none of those had the same break points in their deletion. The main finding in this study was that patients with WHS may have a better outcome regarding motor skills and expressive communication than previously described. We could confirm the main medical findings described earlier, but found also a population with a less severe dysmorphology, fewer congenital malformations, and fewer medical challenges than expected. Sleep problems may persist into adulthood and need a more thorough investigation. Research on possible indications of ASD is strongly needed for targeted interventions. In conclusion, a more thorough assessment of communication, possible ASD, and sleep in larger groups of patients with WHS are needed to confirm and further investigate the findings from this study and to provide more targeted interventions for WHS patients.

Wolf-Hirschhorn Syndrome Candidate 1 Is Necessary for Correct Hematopoietic and B Cell Development

Immunodeficiency is one of the most important causes of mortality associated with Wolf-Hirschhorn syndrome (WHS), a severe rare disease originated by a deletion in chromosome 4p. The WHS candidate 1 (WHSC1) gene has been proposed as one of the main genes responsible for many of thealterations in WHS, but its mechanism of actionis still unknown. Here, we present invivo genetic evidence showing that Whsc1 plays an important role at several points of hematopoietic development. Particularly, our results demonstrate that both differentiation and function of Whsc1-deficient B cells are impaired at several key developmental stages due to profound molecular defects affecting B cell lineage specification, commitment, fitness, and proliferation, demonstrating a causal role for WHSC1 in the immunodeficiency of WHS patients.

Analyses of Genotypes and Phenotypes of Ten Chinese Patients with Wolf-Hirschhorn Syndrome by Multiplex Ligation-dependent Probe Amplification and Array Comparative Genomic Hybridization.

Background:Wolf-Hirschhorn syndrome (WHS) is a contiguous gene syndrome that is typically caused by a deletion of the distal portion of the short arm of chromosome 4. However, there are few reports about the features of Chinese WHS patients. This study aimed to characterize the clinical and molecular cytogenetic features of Chinese WHS patients using the combination of multiplex ligation-dependent probe amplification (MLPA) and array comparative genomic hybridization (array CGH).Methods:Clinical information was collected from ten patients with WHS. Genomic DNA was extracted from the peripheral blood of the patients. The deletions were analyzed by MLPA and array CGH.Results:All patients exhibited the core clinical symptoms of WHS, including severe growth delay, a Greek warrior helmet facial appearance, differing degrees of intellectual disability, and epilepsy or electroencephalogram anomalies. The 4p deletions ranged from 2.62 Mb to 17.25 Mb in size and included LETM1, WHSC1, and FGFR3.Conclusions:The combined use of MLPA and array CGH is an effective and specific means to diagnose WHS and allows for the precise identification of the breakpoints and sizes of deletions. The deletion of genes in the WHS candidate region is closely correlated with the core WHS phenotype.

Airway Management in a Patient with Wolf-Hirschhorn Syndrome.

We present a case of a 3-month-old female with Wolf-Hirschhorn syndrome (WHS) undergoing general anesthesia for laparoscopic gastrostomy tube placement with a focus on airway management. WHS is a rare 4p microdeletion syndrome resulting in multiple congenital abnormalities, including craniofacial deformities. Microcephaly, micrognathia, and glossoptosis are common features in WHS patients and risk factors for a pediatric airway that is potentially difficult to intubate. We discuss anesthesia strategies for airway preparation and management in a WHS patient requiring general anesthesia with endotracheal intubation.

Growth profiles of 34 patients with Wolf-Hirschhorn syndrome.

Wolf-Hirschhorn syndrome (WHS) encompasses multiple congenital anomalies and mental retardation and is caused by partial deletions in the short arm of chromosome 4. Prenatal-onset growth deficiency is one of the WHS characteristics. Assessing and recording growth profiles of patients with WHS were the aims of this study. Anonymous questionnaire surveys were conducted with cooperation of a WHS peer-support group in Japan, and data from 34 WHS patients (12 males and 22 females; age, 1-23 years) were retrospectively collected. Height, weight, and head circumference (occipitofrontal head circumference) were measured and plotted on the standard growth charts of healthy Japanese children. Results indicated that most WHS patients showed growth retardation under the 3rd percentile since the first year of life and extremely poor body-weight gain after pubertal age. These findings are characteristic of WHS patients. The assessed growth patterns in this study could help monitoring and documentation of growth of WHS patients.

Auditory hair cell defects as potential cause for sensorineural deafness in Wolf-Hirschhorn syndrome.

ABSTRACTWHSC1 is a histone methyltransferase (HMT) that catalyses the addition of methyl groups to lysine 36 on histone 3. In humans, WHSC1 haploinsufficiency is associated with all known cases of Wolf-Hirschhorn syndrome (WHS). The cardinal feature of WHS is a craniofacial dysmorphism, which is accompanied by sensorineural hearing loss in 15% of individuals with WHS. Here, we show that WHSC1-deficient mice display craniofacial defects that overlap with WHS, including cochlea anomalies. Although auditory hair cells are specified normally, their stereocilia hair bundles required for sound perception fail to develop the appropriate morphology. Furthermore, the orientation and cellular organisation of cochlear hair cells and their innervation are defective. These findings identify, for the first time, the likely cause of sensorineural hearing loss in individuals with WHS.

LETM1 haploinsufficiency causes mitochondrial defects in Wolf-Hirschhorn syndrome patient cells: implications for dissecting underlying pathomechanisms in this condition

Wolf-Hirschhorn syndrome (WHS) represents an archetypical example of a contiguous gene deletion disorder – a condition comprising a complex set of developmental phenotypes with a multigenic origin. Epileptic seizures, intellectual disability, growth restriction, motor delay and hypotonia are major co-morbidities in WHS. Haploinsufficiency of LETM1, which encodes a mitochondrial inner-membrane protein functioning in ion transport, has been proposed as an underlying pathomechanism, principally for seizures but also for other core features of WHS, including growth and motor delay. Growing evidence derived from several model organisms suggests that reduced LETM1 expression is associated with some element of mitochondrial dysfunction. Surprisingly, LETM1-dependent mitochondrial functional deficits have not previously been described in cells from individuals with WHS. Here, using a unique panel of WHS-patient-derived cell lines with deletions of differing sizes, incorporating LETM1 or not, we show, for the first time, that LETM1 expression is reduced in mitochondria isolated from WHS-patient cells. Furthermore, we show that this is associated with distinct mitochondrial phenotypes, including altered intracellular [Ca2+] levels, dysfunctional mitochondrial transition-pore opening, hyperpolarization and superoxide leakage from resting mitochondria. Interestingly, we find that these phenotypes segregate with seizures in our WHS cohort. Our findings identify novel cellular phenotypes in WHS attributable to a 50% reduction in LETM1 expression level; these phenotypes could underlie and/or contribute to some of the core clinical features of this condition.

Microarray and FISH‐based genotype–phenotype analysis of 22 Japanese patients with Wolf–Hirschhorn syndrome

Wolf-Hirschhorn syndrome (WHS) is a contiguous gene deletion syndrome of the distal 4p chromosome, characterized by craniofacial features, growth impairment, intellectual disability, and seizures. Although genotype-phenotype correlation studies have previously been published, several important issues remain to be elucidated including seizure severity. We present detailed clinical and molecular-cytogenetic findings from a microarray and fluorescence in situ hybridization (FISH)-based genotype-phenotype analysis of 22 Japanese WHS patients, the first large non-Western series. 4p deletions were terminal in 20 patients and interstitial in two, with deletion sizes ranging from 2.06 to 29.42 Mb. The new Wolf-Hirschhorn syndrome critical region (WHSCR2) was deleted in all cases, and duplication of other chromosomal regions occurred in four. Complex mosaicism was identified in two cases: two different 4p terminal deletions; a simple 4p terminal deletion and an unbalanced translocation with the same 4p breakpoint. Seizures began in infancy in 33% (2/6) of cases with small (<6 Mb) deletions and in 86% (12/14) of cases with larger deletions (>6 Mb). Status epilepticus occurred in 17% (1/6) with small deletions and in 87% (13/15) with larger deletions. Renal hypoplasia or dysplasia and structural ocular anomalies were more prevalent in those with larger deletions. A new susceptible region for seizure occurrence is suggested between 0.76 and 1.3 Mb from 4 pter, encompassing CTBP1 and CPLX1, and distal to the previously-supposed candidate gene LETM1. The usefulness of bromide therapy for seizures and additional clinical features including hypercholesterolemia are also described.

Microarray analysis of unbalanced translocation in Wolf‐Hirschhorn syndrome

Wolf-Hirschhorn syndrome (WHS) is caused by deletions involving chromosome region 4p16.3, which is characterized by growth delay, mild-to-severe mental retardation, hypotonia, facial dysmorphisms and shows extensive phenotypic variability include feeding difficulties, epilepsy and congenital anomalies. Variation in the size of the deletion involving chromosome region 4p16.3 may explain the clinical variation. However, previous studies indicate that duplication for another chromosome region due to an unbalanced translocation elucidate approximately 40-45% WHS patients. Therefore, we used whole genomic cytogenetics array to analyze the entire genome at a significantly higher resolution over conventional cytogenetics to characterize the exact subtelomeric aberration region of one patient with developmental delay and several facial characteristics reminiscent Wolf-Hirschhorn syndrome. Here we report that our patient had 3.7 Mb deletion at the 4p16.2 and 6.8 Mb duplication at 8p23.1 resulted from the unbalanced translocations der(4)t(4;8)(p16.2;p23.1). We confirmed that our patient with monosomy 4p16.2 which is consistent with Wolf-Hirschhorn syndrome and trisomy 8p23.1. The combination of the 4p deletion with 8p partial trisomy explains the complex phenotype presented by our patient.

Two cases of hepatic adenomas in patients with wolf‐hirschhorn syndrome: A new rare complication?

Wolf-Hirschhorn syndrome (WHS) is a rare microdeletion syndrome associated with a characteristic facial appearance, failure to thrive, psychomotor delays, and various major malformations of internal organs; many medical complications have been described (feeding difficulties, epilepsy, hearing problems). Benign or malignant oncologic problems are not a typical feature of the natural history of these patients. We report on two patients with WHS patients in whom hepatic adenoma (HA) were diagnosed during adolescence. The clinical evolution of liver involvement was different between the two. We discuss the possibility of considering HA as a rare medical problem in the follow-up of WHS patients. © 2013 Wiley Periodicals, Inc.

1.5 Mb deletion of chromosome 4p16.3 associated with postnatal growth delay, psychomotor impairment, epilepsy, impulsive behavior and asynchronous skeletal development

Several Wolf-Hirschhorn syndrome patients have been studied, mouse models for a few candidate genes have been constructed and two WHS critical regions have been postulated, but the molecular basis of the syndrome remains poorly understood.Single gene contributions to phenotypes of microdeletion syndromes have often been based on the study of patients carrying small, atypical deletions. We report a 5-year-old girl harboring an atypical 1.5Mb del4p16.3 and review seven previously published patients carrying a similar deletion. They show a variable clinical presentation and the only consistent feature is post-natal growth delay. However, four of eight patients carry a ring (4), and ring chromosomes in general are associated with growth deficiency. The Greek helmet profile is absent, although a trend towards common dysmorphic features exists. Variable expressivity and incomplete penetrance might play a role in WHS, resulting in difficult clinical diagnosis and challenge in understanding of the genotype/phenotype correlation.