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.

[Prenatal diagnosis and genetic analysis of two fetuses with Wolf-Hirschhorn syndrome].

OBJETIVE: To explore the prenatal ultrasound phenotype and genetic basis of two fetuses with Wolf-Hirschhorn syndrome (WHS). METHODS: A retrospective analysis was conducted on the ultrasound imaging data of two fetuses suspected for WHS at the Prenatal Diagnostic Center of Qingyuan People's Hospital in July 2017 and August 2019, respectively. Amniotic fluid samples of the two fetuses were subjected to chromosomal karyotyping and chromosomal microarray analysis (CMA). This study was approved by the Qingyuan People's Hospital (Ethics No. IRB-2022-064). RESULTS: Prenatal ultrasound examination of the two fetuses had consistently revealed WHS-associated traits including intrauterine growth restriction (IUGR), craniofacial abnormalities and cardiovascular anomalies. Karyotyping analysis suggested that both fetuses had harbored cryptic chromosomal translocations involving partial deletion of 4p. And parental verification revealed that it was de novo for fetus 1 and paternal for fetus 2. CMA has confirmed that fetus 1 had an approximately 8.7 Mb deletion at 4p16.3p16.1 and a 6.8 Mb duplication at 8p23.1p23.1, whilst fetus 2 had a 20.05 Mb deletion at 4p16.3p15.31 and a 7.66 Mb duplication at 9p24.3p24.1. The karyotype of fetus 1 was determined as 46,XN,der(4)t(4;8)(p16.1;p23.1)dn.arr[hg19]4p16.3p16.1(68345_8721580)×1, 8p23.3p23.1(158048_6933745)×3, and that of fetus 2 was determined as 46,XN,der(4)t(4;9)(p15.3;p24)pat.arr[hg19]4p16.3p15.31(68345_20116061)×1, 9p24.3p24.1(208454_7868292)×3. CONCLUSION: The 4p deletion is probably the main cause for the WHS phenotype in both fetuses. WHS should be suspected when IUGR, renal anomalies, craniofacial and cardiovascular abnormalities are detected upon prenatal ultrasound screening.

The constitutional gain-of-function variant p.Glu1099Lys in NSD2 is associated with a novel syndrome.

NSD2 dimethylates histone H3 at lysine 36 (H3K36me2) and is located in the Wolf-Hirschhorn syndrome (WHS) critical region. Recent descriptions have delineated loss-of-function (LoF) variants in NSD2 with a distinct disorder. The oncogenic missense variant p.Glu1099Lys occurs somatically in leukemia and has a gain-of-function (GoF) effect. We describe two individuals carrying p.Glu1099Lys as heterozygous de novo germline variant identified by exome sequencing (ES) of blood DNA and subsequently confirmed in two ectodermal tissues. Clinically, these individuals are characterized by intellectual disability, coarse/ square facial gestalt, abnormalities of the hands, and organomegaly. Public cell lines with NSD2 GoF variants had increased K36me2, DNA promoter methylation, and dysregulated RNA expression. NSD2 GoF caused by p.Glu1099Lys is associated with a novel phenotype different from WHS and Rauch-Steindl syndrome (RAUST).

Efficacy of Antiseizure Medications in Wolf-Hirschhorn Syndrome.

Wolf-Hirschhorn syndrome (WHS) is caused by deletion of the terminal region of chromosome 4 short arm and is frequently associated with intractable epilepsy. This article evaluates the clinical features of epileptic seizures in WHS and the therapeutic efficacy of oral antiseizure medications (ASMs). Patients with WHS who were treated for epilepsy at the Saitama Children's Medical Center under 5 years of age were included. WHS was diagnosed based on genetic tests and clinical symptoms. Medical records regarding the age of onset of epilepsy, seizure type, treatment of status epilepticus (SE), and effectiveness of ASMs were retrospectively reviewed. Oral ASMs were considered effective when seizures were reduced by at least 50% compared with the premedication level. Eleven patients were included in the study. The median age at the onset of epilepsy was 9 months (range: 5-32 months). Unknown-onset bilateral tonic-clonic seizure was the most common type of seizure, occurring in 10 patients. Focal clonic seizures occurred in four patients. Ten patients exhibited recurrent episodes of SE, and its frequency during infancy was monthly in eight patients and yearly in two. SE occurrence peaked at 1 year of age and decreased after 3 years of age. The most effective ASM was levetiracetam. Although WHS-associated epilepsy is intractable with frequent SE occurrence during infancy, improvement in seizure control is expected with age. Levetiracetam may be a novel ASM for WHS.

Prenatal Diagnosis and Molecular Cytogenetic Analyses of a de novo Deletion on Chromosome 4p16.3p15.33.

Wolf-Hirschhorn syndrome (WHS) (OMIM 194190) is a contiguous gene syndrome with an estimated prevalence of around 1 in 50,000 births. The syndrome is caused by the deletion of a critical region (Wolf-Hirschhorn Syndrome Critical region-WHSCR) on chromosome 4p16.3. Its core features are typical facial gestalt, growth retardation, intellectual disability, developmental delay, and seizures. Prenatal diagnosis of WHS helps clinicians and parents make informed decisions about pregnancy management. In this research, a 31-year-old woman (gravida 1, para 0) underwent amniocentesis at 18 weeks gestation because of the short nasal bone of the fetus on prenatal ultrasound. Chromosomal microarray analysis (CMA) on uncultured amniocytes revealed a de novo 11.36-Mb deletion on chromosome 4p16.3p15.33, spanning from position 40 000 to 11 400 000 (hg19). After genetic counselling and being informed of the unfavorable prognosis, the parents decided to terminate the pregnancy. We provide a detailed description of a de novo 11.36-Mb deletion on chromosome 4p16.3p15.33 (Wolf-Hirschhorn syndrome). CMA has more advantages than karyotype analysis in detecting chromosomal microdeletions/microduplications. A combination of karyotype analysis, CMA, prenatal ultrasound, and genetic counseling is helpful for the prenatal diagnosis of chromosomal deletions/duplications.

Prenatal sonographic findings in confirmed cases of Wolf-Hirschhorn syndrome.

BACKGROUND: Wolf-Hirschhorn syndrome (WHS) is a common genetic condition and prenatal diagnosis is difficult due to heterogeneous expression of this syndrome and rather non-specific ultrasound findings. Objective of this study was to examine the prenatal ultrasound findings in fetuses with Wolf-Hirschhorn syndrome (WHS). METHODS: Retrospective assessment of 18 pregnancies that were seen at three tertiary referral centers (Universities of Bonn, Tuebingen and Nuernberg / Germany). Findings of prenatal ultrasound examinations, genetic results and outcome were compared. Additionally, findings of our study were compared to previous small case series from the literature and then compared to data on postnatal frequencies and abnormalities in affected patients. RESULTS: Median gestational age at the time of examination was 23 + 1 weeks' (range: 13 + 4 to 29 + 1 weeks') with female-to-male ratio of > 2.5:1. Most frequent ultrasound findings were facial abnormalities, symmetric IUGR and microcephaly that presented in 94.4, 83.3 and 72.2% of cases, respectively. The combination of microcephaly and hypoplastic nasal bone was a particularly characteristic finding. Growth retardation presented in all fetuses > 20 weeks, but not below. Other frequent abnormalities included cardiac anomalies in 50 and single umbilical artery (SUA) in 44.4% of fetuses. CONCLUSION: WHS should be considered in the presence of symmetric IUGR together with microcephaly, hypoplastic nasal bone and facial abnormalities on prenatal ultrasound. Genetic testing by chromosomal microarray analysis (CMA) is strongly recommended in this context.

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).

Natural history study of adults with Wolf-Hirschhorn syndrome 1: Case series of personally observed 35 individuals.

Wolf-Hirschhorn syndrome (WHS) is a contiguous gene disorder, clinically delineated by prenatal and postnatal growth deficiency, distinctive craniofacial features, intellectual disability, and seizures. The disorder is caused by partial loss of material from the distal portion of the short arm of chromosome 4 (4p16.3). Although more than 300 persons with WHS have been reported in the literature, there is sparse, if any, long-term follow-up of these individuals and thus little knowledge about course and potential further complications and health risks during adulthood and advanced age. This study attempted to assess medical conditions and function of adult individuals with WHS. It was one component of a two-part investigation on adults with WHS. The other part of the study is the patient-reported outcomes study reported elsewhere. About 35 individuals with WHS (26 females; nine males), aged between 19 and 55 years were recruited. About 25 individuals were personally observed at the IRCCS Stella Maris Foundation by A.B. and followed up between 5 and 20 years; and 10 were recruited from the 4p-Support Group, The United States. Of note, 23/35 (66%) are close to total care. About 11 out of 35 (31%) were partly self-independent, requiring supervision on certain daily routines, and 1 out of 35 (3%) was fully independent. However, a positive perspective is given by the overall good health enjoyed by the 66% of our cohort of individuals. Overall, quality of life and level of function into adulthood appear to be less critical than anticipated from previous studies.

Natural history study of adults with Wolf-Hirschhorn syndrome 2: Patient-reported outcomes study.

Wolf-Hirschhorn syndrome (WHS) is a contiguous gene disorder consisting of prenatal and postnatal growth deficiency, distinctive craniofacial features, intellectual disability, and seizures. The condition is caused by a partial loss of material from the distal portion of the short arm of chromosome 4 (4p16.3). While there are many reports of individuals with WHS, useful data on long-term survival and life status of adults with the syndrome are very limited. There are only 11 reports of individuals over the age of 18 years in the literature. Establishing the medical manifestations of adults with WHS would be helpful in establishing appropriate health supervision guidelines. This study was one component of a two-part investigation on adults with WHS. This patient-reported outcomes study (PROS) was accomplished by using the registry of rare diseases at Sanford Research, Coordination of Rare Diseases (CoRDS)at Sanford. Thirty family members or caretakers of 30 adults with WHS/4p- entered into the CoRDS registry and completed some or all of the survey data. Twelve caretakers completed the recently-added survey on activities of daily living. Two of the individuals with WHS were partly independent while 10 required total care. The results provide novel information on daily life and independence in adults with WHS. Importantly, the majority of caretakers reported that the adults were in good health. The data from both parts of the study will contribute to our knowledge of the natural history of the syndrome and guide in establishing appropriate health supervision guidelines for adults with WHS.

[Study on clinical features and diagnostic methods of prenatal Wolf-Hirschhorn syndrome].

OBJECTIVE: To investigate the clinical features of fetuses with Wolf-Hirschhorn syndrome(WHS) and explore the diagnostic methods and prenatal ultrasound characteristics and provide evidence for prenatal genetic counseling. METHODS: We retrospectively analyzed 5 cases of WHS fetuses diagnosed from March 2016 to February 2020, and analyzed the results of chromosomal karyotype analysis and chromosomal microarray analysis (CMA) of the fetuses. RESULTS: Five cases of WHS were detected by CMA, four cases were detected by karyotype analysis. Prenatal ultrasound revealed 4 abnormalities, of which 3 had intrauterine growth restriction, and only 1 had abnormalities of the maxillofacial region. The sequence of the fragments was 4p16.3p16.1 with a loss of 6.5 Mb, 4p16.3p15.32 with a loss of 15.6 Mb combined with 2p25.3 increased by 906kb, 4p16.3p15.31 with a loss of 20.4 Mb, 4p16.p15.1 with a loss of 35 Mb and 4p16.3p14 with a loss of 37 Mb. CONCLUSION: Fetal growth restriction may be one of the early manifestations of WHS. Absence of fetal facial abnormality by prenatal ultrasound screening cannot exclude WHS. Karyotype analysis may miss the diagnosis of WHS, while combined CMA techniques can improve the diagnostic accuracy.

Wolf-Hirschhorn syndrome: A case series from India.

Wolf-Hirschhorn syndrome (WHS) (OMIM#194190) is a contiguous gene syndrome with estimated prevalence being around 1 in 50,000 births. The syndrome is caused by deletion of a critical region (Wolf-Hirschhorn Syndrome Critical region-WHSCR) on chromosome 4p16.3. Its core features are typical facial gestalt, growth retardation, intellectual disability, or developmental delay and seizures. We describe four patients, each highlighting a different aspect of this syndrome. One patient was detected by karyotype where a large deletion was identified. Three other children were diagnosed after targeted multiplex ligation-dependent probe amplification (MLPA) where heterozygous deletion of the probes on chromosome 4p16.3 were identified. One of these children additionally had heterozygous duplication of the probe for chromosome band 5p13.3. Less than half of the patients can be identified by conventional cytogenetics and molecular cytogenetic testing should be offered for diagnosis. Karyotyping of the parents should always be offered in a child with WHS.

International meeting on Wolf-Hirschhorn syndrome: Update on the nosology and new insights on the pathogenic mechanisms for seizures and growth delay.

"An International Meeting on Wolf-Hirschhorn Syndrome (WHS)" was held at The University Hospital La Paz in Madrid, Spain (October 13-14, 2017). One hundred and twenty-five people, including physicians, scientists and affected families, attended the meeting. Parent and patient advocates from the Spanish Association of WHS opened the meeting with a panel discussion to set the stage regarding their hopes and expectations for therapeutic advances. In keeping with the theme on therapeutic development, the sessions followed a progression from description of the phenotype and definition of therapeutic endpoints, to definition of genomic changes. These proceedings will review the major points of discussion.

Melatonin reverses the oxidative stress and mitochondrial dysfunction caused by LETM1 silencing.

LETM1 is a mitochondrial inner-membrane protein, which is encoded by a gene present in a locus of 4p, which, in turn, is deleted in the Wolf-Hirschhorn Syndrome, and is assumed to be related to its pathogenesis. The cellular damage caused by the deletion is presumably related to oxidative stress. Melatonin has many beneficial roles in protecting mitochondria by scavenging reactive oxygen species, maintaining membrane potential, and improving functions. The aim of this study was to investigate the effects of melatonin administration to LETM1-silenced mouse embryonic fibroblast cells as a cellular model for LETM1 deficiency. We transfected mouse embryonic fibroblast cells with a pair of siRNA against LETM1 and monitored the oxidative stress and mitochondrial functions with or without melatonin addition. MnSOD expression and aconitase activity decreased and oxidized protein levels increased in LETM1-silenced cells. LETM1 suppression did not alter the expression of OXPHOS complexes, but the oxygen consumption rates decreased significantly; however, this change was not related to complex I but instead involved complex IV and complex II. Melatonin supplementation effectively normalized the parameters studied, including the oxygen consumption rate. Our findings identified a novel effect of LETM1 deficiency on cellular respiration via complex II as well as a potential beneficial role of melatonin treatment. On the other hand, these effects may be specific to the cell line used and need to be verified in other cell lines.

[Identification of a critical region on chromosome 4p16.3 for Wolf-Hirschhorn syndrome-associated fetal growth retardation].

OBJECTIVE: To analyze ultrasonographic finding in fetuses with Wolf-Hirschhorn syndrome (WHS) and refine the critical region on chromosome 4p16.3 for WHS-associated fetal growth retardation (FGR). METHODS: In total 2262 fetuses with abnormal ultrasonographic findings who underwent prenatal karyotyping and chromosomal microarray analysis were reviewed. WHS-associated 4p deletions detected in these fetuses were compared, and prenatal ultrasound findings in such fetuses were summarized. Meanwhile, WHS cases with prenatal ultrasound findings and isolated 4p deletions in previous studies were included for further analysis. An analysis of smallest region of overlap (SRO) among discrepant 4p deletions in these cases above was performed to define a critical region for FGR. RESULTS: 4p deletions were detected in 10 of the 2262 fetuses and 5.0% of the 202 fetuses with FGR. Combined with 80 WHS cases from previous studies, the most common prenatal ultrasound finding was FGR, which yielded a frequency of 76.7%. In addition, a SRO spanning approximately 419 kb (genomic position: 1.32-1.74 Mb) on chromosome 4p16.3 was discovered by comparing the unusual 4p deletions among the 10 fetuses. The region contained seven protein-coding genes, including TACC3, SLBP, TMEM129, FAM53A, MAEA, UVSSA and CRIPAK. CONCLUSION: For fetuses with WHS, the most common prenatal ultrasound phenotype was FGR. A region between 1.32 Mb to 1.74 Mb from the telomere on chromosome 4p16.3 is critical for WHS-associated FGR, for which TACC3 and SLBP are the candidate genes.

De novo truncating variants in WHSC1 recapitulate the Wolf-Hirschhorn (4p16.3 microdeletion) syndrome phenotype.

PURPOSE: Wolf-Hirschhorn syndrome (WHS) is a genomic disorder with a recognizable dysmorphology profile caused by hemizygosity at 4p16.3. Previous attempts have failed to map the minimal critical locus to a single gene, leaving open the possibility that the core phenotypic components of the syndrome are caused by the combined haploinsufficiency of multiple genes. METHODS: Clinical exome sequencing and "reverse" phenotyping. RESULTS: We identified two patients with de novo truncating variants in WHSC1, which maps to the WHS critical locus. The phenotype of these two individuals is consistent with WHS, which suggests that haploinsufficiency of WHSC1 is sufficient to recapitulate the core phenotype (characteristic facies, and growth and developmental delay) of this classic microdeletion syndrome. CONCLUSION: Our study expands the list of microdeletion syndromes that are solved at the single-gene level, and establishes WHSC1 as a disease gene in humans. Given the severe nature of the reported variants, the full phenotypic expression of WHSC1 may be further expanded by future reports of milder variants.

De novo truncating variant in NSD2gene leading to atypical Wolf-Hirschhorn syndrome phenotype.

BACKGROUND: Wolf-Hirschhorn syndrome (WHS) is a contiguous gene syndrome caused by partial 4p deletion highly variable in size in individual patients. The core WHS phenotype is defined by the association of growth delay, typical facial characteristics, intellectual disability and seizures. The WHS critical region (WHSCR) has been narrowed down and NSD2 falls within this 200 kb region. Only four patients with NSD2 variants have been documented with phenotypic features in detail. CASE PRESENTATION: Herein, we report the case of a 12-year-old boy with developmental delay. He had dysmorphic facial features including wide-spaced eyes, prominent nasal bridge continuing to forehead, abnormal teething and micrognathia. He also had mild clinodactyly of both hands. Using whole-exome sequencing, we identified a pathogenic mutation in NSD2 [c.4029_4030insAA, p.Glu1344Lysfs*49] isolated from peripheral blood DNA. Sanger confirmation of this variant revealed it as a de novo truncating variant in the family. CONCLUSION: Here, we reported a boy with de novo truncating variant in NSD2 with atypical clinical features comparing with 4p16.3 deletion related WHS. Our finding further supported the pathogenesis of truncating variants in NSD2 and delineated the possible symptom spectrum caused by these variants.

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.

[Prenatal diagnosis for a pedigree affected with Wolf-Hirschhorn syndrome due to a subtle chromosomal translocation].

OBJECTIVE: To make molecular diagnosis of an infant affected with severe developmental delay and multiple birth defects, assisting prenatal diagnosis for the second pregnancy. METHODS: Standard G-banded karyotyping was performed for the fetus and his parents. Single nucleotide polymorphism array (SNP array) was used to detect submicroscopic chromosomal aberration. Fluorescence in situ hybridization (FISH) was employed to determine the parental origin of the aberration. RESULTS: Both the proband and the fetus harbored a 5.4 Mb distal 4p deletion and a 6.9 Mb distal 6q duplication. FISH confirmed that the mother has carried a balanced translocation involving 4p and 6q. CONCLUSION: The unbalanced chromosomal aberration in the proband and the fetus were both derived from the mother. Both patients showed a Wolf-Hirschhorn syndrom phenotype and partial phenotype of 6q trisomy. SNP array combined with FISH are essential for the detection of cryptic chromosomal aberrations which may be missed by coventional karyotyping analysis.

De novo nonsense mutation in WHSC1 (NSD2) in patient with intellectual disability and dysmorphic features.

Intellectual disability is the most common developmental disorder caused by chromosomal aberrations as well as single-nucleotide variants (SNVs) and small insertions/deletions (indels). Here we report identification of a novel, probably pathogenic mutation in the WHSC1 gene in a patient case with phenotype overlapping the features of Wolf-Hirschhorn syndrome. Deletions involving WHSC1 (Wolf-Hirschhorn syndrome candidate 1 gene) were described earlier in patients with Wolf-Hirschhorn syndrome. However, to our knowledge, single-point mutations in WHSC1 associated with any intellectual deficiency syndromes have not been reported. Using whole exome sequencing, we found a de novo nonsense mutation in WHSC1 (c.3412C>T, p.Arg1138Ter, NM_001042424.2) in patient with syndromic intellectual disability. This finding is challenging regarding a possible causative role of WHSC1 in intellectual disability syndromes, specifically Wolf-Hirschhorn syndrome. From the clinical standpoint, our finding suggests that next-generation sequencing along with chromosome microarray analysis (CMA) might be useful in genetic testing for patients with intellectual disability and dysmorphic features.

Developmental delay and failure to thrive associated with a loss-of-function variant in WHSC1 (NSD2).

Wolf-Hirschhorn syndrome (WHS) is a microdeletion syndrome characterized by distinctive facial features consisting of "Greek warrior helmet" appearance, prenatal and postnatal growth deficiency, developmental disability, and seizures. This disorder is caused by heterozygous deletions on chromosome 4p16.3 often identified by cytogenetic techniques. Many groups have attempted to identify the critical region within this deletion to establish which genes are responsible for WHS. Herein, clinical whole exome sequencing (WES) was performed on a child with developmental delays, mild facial dysmorphisms, short stature, failure to thrive, and microcephaly, and revealed a de novo frameshift variant, c.1676_1679del (p.Arg559Tfs*38), in WHSC1 (NSD2). While WHSC1 falls within the WHS critical region, individuals with only disruption of this gene have only recently been described in the literature. Loss-of-function de novo variations in WHSC1 were identified in large developmental delay, autism, diagnostic, and congenital cardiac cohorts, as well as recent case reports, suggesting that de novo loss-of-function WHSC1 variants may be related to disease. These findings, along with our patient suggest that loss-of-function variation in WHSC1 may lead to a mild form of Wolf-Hirschhorn syndrome, and also may suggest that the developmental delays, facial dysmorphisms, and short stature seen in WHS may be due to disruption of WHSC1 gene.