Phenotypic and molecular characterisation of the Aarskog–Scott syndrome: a survey of the clinical variability in light of FGD1 mutation analysis in 46 patients

Aarskog Syndrome: Deep Phenotyping and Genomic Landscape of a New Cohort Including Adult Patients

Aarskog-Scott syndrome (AAS, MIM#305400) is an X-linked disorder characterized by recognizable facial features, short stature, and genitourinary and skeletal malformations. AAS is attributed to pathogenic variants in FGD1, and ~60 patients with a genetic diagnosis have been reported to date. We hereby present a molecularly confirmed cohort of 14 male AAS patients from 13 families. Among 14 patients, 12 were referred during childhood, while two were referred at adulthood due to infertility. Six out of 11 patients with available records had antenatal manifestations, comprising shortened tubular bones, growth restriction, polyhydramnios, pes equinovarus, increased nuchal translucency, fetal hypokinesia, echogenic intracardiac focus, and ambiguous genitalia. In addition to well-described AAS findings, distinctive features observed in multiple patients included variable skin findings (n = 5), renal malformations (n = 2), muscular build (n = 2), and infertility (n = 2). Cardiac (n = 4) and ocular manifestations (n = 6) were identified at significantly higher rates than previously reported. This cohort also presents new patients with osteochondritis dissecans and oligo/azoospermia, providing further evidence to acknowledge these once-reported findings as part of the disease spectrum. Eleven different FGD1 variants, including seven novel ones, were identified through targeted FGD1 sequencing. Two variants were found to be recurrent, detected in two independent families. Our study provides additional insights into the clinical and genotypic landscape of AAS through the largest molecularly confirmed cohort, including two adult patients.

Aarskog-Scott syndrome: a clinical study based on a large series of 111 male patients with a pathogenic variant in FGD1 and management recommendations

BACKGROUND

Aarskog-Scott syndrome (AAS) is a rare condition with multiple congenital anomalies, caused by hemizygote variants in the FGD1 gene. Its description was based mostly on old case reports, in whom a molecular diagnosis was not always available, or on small series. The aim of this study was to better delineate the phenotype and the natural history of AAS and to provide clues for the diagnosis and the management of the patients.

METHODS

Phenotypic characterisation of the largest reported AAS cohort, comprising 111 male patients with proven causative variants in FGD1, through comprehensive analyses of clinical data including congenital anomalies, growth and neurodevelopment. Review of photographs and radiographs by experts in dysmorphology and skeletal disorders.

RESULTS

This study refines the phenotypic spectrum of AAS, with the description of new morphological and radiological features, and refines the prevalence of the features. Short stature is less frequent than previously reported and has a prenatal onset in more than half of the patients. The growth has a specific course with a catch-up during the first decade often leading to low-normal stature in adulthood. Whereas intellectual disability is rare, patients with AAS have a high prevalence of specific learning difficulties and attention hyperactivity disorder. In light of this better knowledge of AAS, we provide management recommendations.

CONCLUSION

A better knowledge of the natural history and phenotypic spectrum of AAS will be helpful for the clinical diagnosis and for the interpretation of FGD1 variants using a retrophenotyping strategy, which is becoming the most common way of diagnosis nowadays. Recommendations for care will improve the management of the patients.

Precise subcellular targeting approaches for organelle-related disorders

Pharmacological research has expanded to the nanoscale level with advanced imaging technologies, enabling the analysis of drug distribution at the cellular organelle level. These advances in research techniques have contributed to the targeting of cellular organelles to address the fundamental causes of diseases. Beyond navigating the hurdles of reaching lesion tissues upon administration and identifying target cells within these tissues, controlling drug accumulation at the organelle level is the most refined method of disease management. This approach opens new avenues for the development of more potent therapeutic strategies by delving into the intricate roles and interplay of cellular organelles. Thus, organelle-targeted approaches help overcome the limitations of conventional therapies by precisely regulating functionally compartmentalized spaces based on their environment. This review discusses the basic concepts of organelle targeting research and proposes strategies to target diseases arising from organelle dysfunction. We also address the current challenges faced by organelle targeting and explore future research directions.

FGD1-related Aarskog-Scott syndrome: Identification of four novel variations and a literature review of clinical and molecular aspects

Patients with Aarskog-Scott syndrome (AAS) have short stature, facial anomalies, skeletal deformities, and genitourinary malformations. FYVE, RhoGEF, and PH domain-containing 1 (FGD1) is the only known causative gene of AAS. However, the diagnosis of AAS remains difficult, and specific treatments are still absent. Patients suspected with AAS were recruited, and clinical information was collected. Genetic testing and functional analysis were carried out for the diagnosis. By literature review, we summarized the clinical and genetic characteristics of FGD1-related AAS and analyzed the genotype-phenotype correlation. Five patients were recruited, and four novel FGD1 variants were identified. The diagnosis of AAS was confirmed by genetic analysis and functional study. Three patients treated with growth hormone showed improved heights during the follow-up period. By literature review, clinical features of AAS patients with FGD1 variants were summarized. Regarding FGD1 variations, substitutions were the most common form, and among them, missense variants were the most frequent. Moreover, we found patients with drastic variants showed higher incidences of foot and genitourinary malformations. Missense variants in DH domain were related to a lower incidence of cryptorchidism.   Conclusion: We reported four novel pathogenic FGD1 variations in AAS patients and confirmed the efficacy and safety of growth hormone treatment in FGD1-related AAS patients with growth hormone deficiency. Additionally, our literature review suggested the crucial role of DH domain in FGD1 function. What is Known: • Aarskog-Scott syndrome is a rare genetic disease, and the only known cause is the variant in FGD1 gene. The typical clinical manifestations of AAS include facial, skeletal, and urogenital deformities and short stature. What is New: • We reported four novel FGD1 variants and reported the treatment of growth hormone in FGD1-related AAS patients. Our genotype-phenotype correlation analysis suggested the crucial role of DH domain in FGD1 function.

Velopharyngeal Characteristics in Aarskog-Scott Syndrome: A Case Report

Aarskog-Scott syndrome (AAS), also known as facio-digito-genital syndrome, is a rare heterogenous syndrome characterized by facial dysmorphism, brachydactyly, and genetic abnormalities. Although severe craniofacial abnormalities have been reported in AAS, little is known about speech and resonance issues in AAS. Specifically, published data to date have only indicated reports of hypernasality associated with a cleft palate in AAS. This case report provides clinical and anatomic information surrounding hypernasal speech in the absence of an overt cleft palate in a patient with AAS.

Parallel kinase pathways stimulate actin polymerization at depolarized mitochondria

Mitochondrial damage (MtD) represents a dramatic change in cellular homeostasis, necessitating metabolic changes and stimulating mitophagy. One rapid response to MtD is a rapid peri-mitochondrial actin polymerization termed ADA (acute damage-induced actin). The activation mechanism for ADA is unknown. Here, we use mitochondrial depolarization or the complex I inhibitor metformin to induce ADA. We show that two parallel signaling pathways are required for ADA. In one pathway, increased cytosolic calcium in turn activates PKC-β, Rac, WAVE regulatory complex, and Arp2/3 complex. In the other pathway, a drop in cellular ATP in turn activates AMPK (through LKB1), Cdc42, and FMNL formins. We also identify putative guanine nucleotide exchange factors for Rac and Cdc42, Trio and Fgd1, respectively, whose phosphorylation states increase upon mitochondrial depolarization and whose suppression inhibits ADA. The depolarization-induced calcium increase is dependent on the mitochondrial sodium-calcium exchanger NCLX, suggesting initial mitochondrial calcium efflux. We also show that ADA inhibition results in enhanced mitochondrial shape changes upon mitochondrial depolarization, suggesting that ADA inhibits these shape changes. These depolarization-induced shape changes are not fragmentation but a circularization of the inner mitochondrial membrane, which is dependent on the inner mitochondrial membrane protease Oma1. ADA inhibition increases the proteolytic processing of an Oma1 substrate, the dynamin GTPase Opa1. These results show that ADA requires the combined action of the Arp2/3 complex and formin proteins to polymerize a network of actin filaments around mitochondria and that the ADA network inhibits the rapid mitochondrial shape changes that occur upon mitochondrial depolarization.

Novel truncating variants in FGD1 detected in two Danish families with Aarskog-Scott syndrome and myopathic features

Aarskog–Scott syndrome (AAS) is a developmental disorder, caused by disease‐causing hemizygous variants in the FGD1 gene. AAS is characterized by dysmorphic features, genital malformation, skeletal anomalies, and in some cases, intellectual disability and behavioral difficulties. Myopathy has only been reported once in two affected siblings diagnosed with AAS. Only few adult cases have been reported. This article reports four adults with AAS (three male cases and one female carrier) from two unrelated Danish families, all males presented with variable features suggestive of myopathy. All four carried novel hemizygous pathogenic variants in the FGD1 gene; one family presented with the c.2266dup, p.Cys756Leufs*19 variant while the c.527dup; p.Leu177Thrfs*40 variant was detected in the second family. All males had some mild myopathic symptoms or histological abnormalities. Case 1 had the most severe myopathic phenotype with prominent proximal muscular fatigue and exercise intolerance. In addition, he had multiple deletions of mtDNA and low respiratory chain activity. His younger nephew, case 3, had difficulties doing sports in his youth and had a mildly abnormal muscle biopsy and relatively decreased mitochondrial enzyme activity. The singular case from family 2 (case 4), had a mildly myopathic muscle biopsy, but no overt myopathic symptoms. Our findings suggest that myopathic involvement should be considered in AAS.

The RhoGEF Trio: A Protein with a Wide Range of Functions in the Vascular Endothelium

Many cellular processes are controlled by small GTPases, which can be activated by guanine nucleotide exchange factors (GEFs). The RhoGEF Trio contains two GEF domains that differentially activate the small GTPases such as Rac1/RhoG and RhoA. These small RhoGTPases are mainly involved in the remodeling of the actin cytoskeleton. In the endothelium, they regulate junctional stabilization and play a crucial role in angiogenesis and endothelial barrier integrity. Multiple extracellular signals originating from different vascular processes can influence the activity of Trio and thereby the regulation of the forementioned small GTPases and actin cytoskeleton. This review elucidates how various signals regulate Trio in a distinct manner, resulting in different functional outcomes that are crucial for endothelial cell function in response to inflammation.

A novel truncating variant in the FGD1 gene associated with Aarskog-Scott syndrome in a family previously diagnosed with Tel Hashomer camptodactyly

Tel Hashomer camptodactyly syndrome is a long-known entity characterized by camptodactyly with muscular hypoplasia, skeletal dysplasia, and abnormal palmar creases. Currently, the genetic basis for this disorder is unknown, thus there is a possibility that this clinical presentation may be contained within another genetic diagnosis. Here, we present a multiplex family with a previous clinical diagnosis of Tel Hashomer camptodactyly syndrome. Whole exome sequencing and pedigree-based analysis revealed a novel hemizygous truncating variant c.269_270dup (p.Phe91Alafs*34) in the FGD1 gene (NM_004463.3) in all three symptomatic patients, congruous with a diagnosis of Aarskog-Scott syndrome. Our report adds to the limited data on Aarskog-Scott syndrome, and emphasizes the importance of unbiased comprehensive molecular testing toward establishing a diagnosis for genetic syndromes with unknown genetic basis.

Aarskog-Scott syndrome: phenotypic and genetic heterogeneity

Aarskog-Scott syndrome (AAS) is a rare developmental disorder which primarily affects males and has a relative prevalence of 1 in 25,000 in the general population. AAS patients usually present with developmental complications including short stature and facial, skeletal and urogenital anomalies. The spectrum of genotype-phenotype correlations in AAS is unclear and mutations of the FGD1 gene on the proximal short arm of chromosome X account for only 20% of the incidence of the disorder. Failure to identify pathogenic variants in patients referred for FGD1 screening suggests heterogeneity underlying pathophysiology of the condition. Furthermore, overlapping features of AAS with several other developmental disorders increase the complexity of diagnosis. Cytoskeletal signaling may be involved in the pathophysiology of AAS. The FGD1 protein family has a role in activation of CDC42 (Cell Division Control protein 42 homolog) which has a core function in remodeling of extracellular matrix and the transcriptional activation of many modulators of development. Therefore, mutations in components in the EGFR1 (Epidermal Growth Factor Receptor 1) signaling pathway, to which CDC42 belongs, may contribute to pathophysiology. Parallel sequencing strategies (so-called next generation sequencing or high throughput sequencing) enables simultaneous production of millions of sequencing reads that enormously facilitate cost-effective identification of cryptic mutations in heterogeneous monogenic disorders. Here we review the source of phenotypic and genetic heterogeneity in the context of AAS and discuss the applicability of next generation sequencing for identification of novel mutations underlying AAS.

A novel frameshift mutation in the FGD1 gene causing Aarskog-Scott syndrome patient with hypogonadism: a case report

Aarskog-Scott syndrome (AAS) is most commonly inherited as an X-linked recessive genetic disease caused by FGD1 mutations. AAS patients are most frequently male, and the clinical manifestations of facial abnormalities, skeletal deformities, and abnormal genitalia comprise a characteristic triad of diagnostic features. The results on the clinical and molecular analysis of a family that reveals a novel FGD1 gene frameshift mutation in an 11-year-old boy displaying bilateral cryptorchidism associated with hypogonadism are reported here. This patient exhibited a characteristic triad of diagnostic features of ASS, including short stature, facial abnormalities, joint laxity, and typical scrotal fold. Whole-exome sequencing revealed the novel hemizygous mutation c.500delA in exon 3 of the patient's FGD1 gene, resulting after a frameshift in the Tyr167 residue, while his mother is heterozygous of the same variant. Further in silico studies were performed to identify the pathological consequence of this gene mutation. Thus, our study shows that frameshifts disrupting the RhoGEF gene domain of FGD1 represent the most prevalent causal mutations underlying AAS and expand the phenotypic and mutational spectra of this disease. Improved understanding of the phenotypic and pathological heterogeneity accompanying FGD1 mutation can greatly enhance the clinical prognostic capabilities in the future and aid genetic counseling for AAS patients.

The Prevalence of Clinical Features in Patients with Aarskog-Scott Syndrome and Assessment of Genotype-Phenotype Correlation: A Systematic Review

Aarskog–Scott syndrome is a genetically and clinically heterogeneous rare condition caused by a pathogenic variant in the FGD1 gene. A systematic review was carried out to analyse the prevalence of clinical manifestations found in patients, as well as to evaluate the genotype-phenotype correlation. The results obtained show that clinical findings of the craniofacial, orthopaedic, and genitourinary tract correspond to the highest scores of prevalence. The authors reclassified the primary, secondary, and additional criteria based on their prevalence. Furthermore, it was possible to observe, in accordance with previous reports, that the reported phenotypes do not present a direct relation to the underlying genotypes.

Identifying the potential regulators of neutrophils recruitment in hepatocellular carcinoma using bioinformatics method

BACKGROUND

Neutrophils play a crucial role in the development and progression of hepatocellular carcinoma (HCC); however, the mechanism underlying neutrophil recruitment is not fully understood. Therefore, we aimed to explore the potential genes or pathways related to neutrophil recruitment in the cancer microenvironment.

METHODS

We downloaded TCGA HCC gene expression profiles, the abundance of 22 different immune cells in HCC patients, and patient survival information. We used Kaplan-Meier survival analysis to determine if neutrophils were related to survival. Next, we screened different expression genes (DEGs) between patients with high and low level of neutrophils. We then identified the transcription factor and its targets in the fence of DEGs. Then, we carried out enrichment analysis and gene set variation analysis (GSVA) for targets. Finally, we explored the potential mechanism of targets via calculating correlation scores.

RESULTS

Our survival analysis results showed that neutrophils were significantly associated with patient survival. A total of 736 DEGs were screened. Next, we identified transcription factor larger E26 transformation-specific (ETS) homologous factor (EHF) and 702 targets of EHF from 736 DEGs. Among these targets, the level of FGD6 expression had the highest correlation with the level of EHF expression. Enrichment and GSVA analysis for FGD6 showed that the level of GO:0043547 had a positive regulatory effect on GTPase activity and the GO:0007010 cytoskeleton organization was significantly difference between the high and low neutrophils counts. By calculating the correlation between FGD6 and genes in GO:0043547 and GO:0007010, we identified RIC8B and SIPA1L3.

CONCLUSIONS

These findings demonstrated that transcription factor EHF can influence recruitment of neutrophils by mediating the transcription of FGD6. Further investigations are needed to shed new light on EHF and its target FGD6.

Smad anchor for receptor activation nuclear localization during development identifies Layers V and VI of the neocortex

Smad anchor for receptor activation (SARA, zfyve9) has been classically observed in early endosomes of different cells types where it regulates vesicular transport of proteins and membrane components. Very few other members of the zinc finger FYVE domain-containing family (zfyve) have different functions other than controlling membrane trafficking. By analyzing SARA localization throughout mouse embryonic brain development, we detected that besides the endosomal localization it also targets neuronal nuclei, specifically of the cortical layers V/VI. These findings were confirmed in human brain organoids. When evaluating neuronal cell lines, we found that SARA accumulates in nuclei of PC-12 cells, but not Neuro-2a, highlighting its specificity. SARA functions as a specific marker of the deep cortical layers until the first postnatal week. This temporal regulation corresponds with the final phases of neuron differentiation, such as soma ventral translocation and axonal targeting. In sum, here we report that SARA localization during brain development is temporarily regulated, and layer specific. This defined pattern helps in the identification of early born cortical neurons. We further show that other zfyve family members (FYCO1, WDFY3, Hrs) also distribute to nuclei of different cells in the brain cortex, which raises the possibility that this might be an extended feature within the protein family.

Aarskog-Scott syndrome: clinical and molecular characterisation of a family with the coexistence of a novel FGD1 mutation and 16p13.11-p12.3 microduplication

Aarskog-Scott syndrome (AAS), also known as facio-genital dysplasia or faciodigitogenital syndrome, is a rare genetic disorder clinically characterised by facial, limb and genitalanomalies. Although also autosomal dominance and recessive patterns have been reported, up to now, only an X linked form associated to mutations of the FGD1 gene has been recognised as causative for this syndrome.In this case report, we describe a large Italian family in which three members across three generations show classical features of the syndrome. The youngest patient, the proband, and his mother were both molecularly studied and characterised for the not previously reported variant c.1828C>T (p. Arg610*) in the FGD1 gene but with the classic phenotype of AAS. Additionally, both the proband and his mother present a 2.5 Mb 16p13.11-p12.3 microduplication, a genetic variant still unclear for the phenotypic consequences: the co-occurrence of the two rare conditions is discussed for the possible clinical significance.

Philtrum length and intercommissural distance measurements at mixed dentition period

Anthropometric measurements of the lip and mouth are of great importance in clinical dysmorphology as well as reconstructive plastic surgery. In this study, the philtrum length (PhL) and intercommissural distance (ICmD) nomograms for Egyptian children in the mixed dentition period were established. A group of 1,338 Egyptian students in primary schools (735 boys and 603 girls) were included in the study. The students were at mixed dentition period and their ages ranged from 7 to 12 years. Anthropometric norms of PhL and ICmD were developed with significant sex difference in certain groups. A ratio between PhL and ICmD was developed. These data will help facilitate both objective and subjective evaluation of the lip and mouth for proper diagnosis of orofacial anomalies and variations as well as for ideal treatment plans.

Genetics of Short Stature

Short stature is a common and heterogeneous condition that is often genetic in etiology. For most children with genetic short stature, the specific molecular causes remain unknown; but with advances in exome/genome sequencing and bioinformatics approaches, new genetic causes of growth disorders have been identified, contributing to the understanding of the underlying molecular mechanisms of longitudinal bone growth and growth failure. Identifying new genetic causes of growth disorders has the potential to improve diagnosis, prognostic accuracy, and individualized management, and help avoid unnecessary testing for endocrine and other disorders.

Novel variant in the FGD1 gene causing Aarskog-Scott syndrome

Aarskog-Scott syndrome (ASS) is a rare, X-linked recessive inherited disorder. Affected individuals may develop short stature and exhibit distinctive skeletal and genital development. Mutations in the FYVE, rhogef and pleckstrin homology domain-containing protein 1 (FGD1) gene, located within the Xp11.21 region, are responsible for the occurrence of ASS. Since it is rare and complex, it can take a long time to obtain a definitive clinical diagnosis unless clinicians are familiar with the disease. In the present study, whole-exome sequencing (WES) was performed to screen for causal variants in a Chinese pediatric patient who exhibited a number of clinical symptoms of ASS, including short stature, facial abnormalities, stubby metacarpals and swollen testis. DNA sequencing revealed a novel c.1270 A>G mutation in exon 6 of the FGD1 gene, which led to an amino acid conversion of asparagine to aspartic acid on codon 424 and in silico analysis indicated that this novel missense mutation was pathogenic. The present study identified a novel variant of the FGD1 gene and to the best of our knowledge, is the first report of ASS in a Chinese individual. The results indicated that WES is an effective tool for the diagnosis of rare and complex syndromes such as ASS.

A novel, putatively null, FGD1 variant leading to Aarskog-Scott syndrome in a family from UAE

BACKGROUND

The X-linked condition "Aarskog-Scott syndrome (AAS)" causes a characteristic combination of short stature, facial, genital and skeletal anomalies. Studies elucidated a causative link between AAS and mutations in the FGD1 gene, which encodes a Rho/Rac guanine exchange factor. FGD1 is involved in regulating signaling pathways that control cytoskeleton organization and embryogenesis.

CASE PRESENTATION

FGD1 was studied in an Emirati family with two cases of AAS using PCR amplification and direct sequencing of the entire coding region of the gene. Various in silico tools were also used to predict the functional consequences of FGD1 mutations. In the reported family, two brothers harbor a novel hemizygous mutation in FGD1 c.53del (p.Pro18Argfs*106) for which the mother is heterozygous. This frameshift deletion, being close to N-terminus of FGD1, is predicted to shift the reading frame in a way that it translates to 105 erroneous amino acids followed by a premature stop codon at position 106. Full molecular and clinical accounts about the variant are given so as to expand molecular and phenotypical knowledge about this disorder.

CONCLUSIONS

A novel variant in FGD1 was found in an Emirati family with two brothers suffering from AAS. The variant is predicted to be a null mutation, and this is the first report of its kind from the United Arab Emirates.

A novel splice site mutation of FGD1 gene in an Aarskog-Scott syndrome patient with a large anterior fontanel

Aarskog-Scott syndrome (ASS) is a rare X-linked recessive genetic disorder caused by FGD1 mutations. FGD1 regulates the actin cytoskeleton and regulates cell growth and differentiation by activating the c-Jun N-terminal kinase signaling cascade. ASS is characterized by craniofacial dysmorphism, short stature, interdigital webbing and shawl scrotum. However, there is a wide phenotypic heterogeneity because of the additional clinical features. ASS and some syndromes including the autosomal dominant inherited form of Robinow syndrome, Noonan syndrome, pseudohypoparathyroidism, Silver-Russel and SHORT syndrome have some overlapping phenotypic features. Herein, we report a patient with ASS and a large anterior fontanel who was initially diagnosed as Robinow syndrome. He was found to have a novel c.1340+2 T>A splice site mutation on the FGD1 gene.

Association of FGD1 polymorphisms with early-onset breast cancer

Recent cancer studies have suggested that the faciogenital dysplasia 1 (FGD1) gene may play a role in the development of tumor cells. Somatic alterations in the FGD1 gene and increased Fgd1 protein expression have been observed in many breast tumor cases. The present study sequenced the FGD1 gene in tumor DNA from 46 breast cancer patients using Ion Torrent sequencing. Three synonymous polymorphisms and one missense polymorphism were detected with next-generation sequencing; however, no somatic mutations were observed. The Thr697 variant was identified in 18 patients with an average age at diagnosis of 55 years, which was a lower average age than patients without the polymorphism. In addition, a higher frequency of Thr697 was observed in African-American patients. The Pro712 was observed in 15 breast cancer patients with an average age of 58 years, and was observed as a haplotype with the Thr697 variant in 28% of the breast cancer patients studied. The missense polymorphism (Ala226Thr) was identified in a 40-year-old female patient who had a recurrence of cancer. These polymorphisms (Ala226Thr, Thr697 and Pro712) may be associated with an earlier onset of breast cancer.

Minireview: Role of genetic changes of faciogenital dysplasia protein 1 in human disease

The FGD1 gene encodes for a guanine exchange factor (GEF) protein that specifically activates the Rho GTPase Cdc42. For cellular migration, Cdc42 is a key molecular switch that regulates cytoskeleton restructuring, gene transcription, cellular morphology, extension, and cell adhesion. In the past decade, germline mutations in the FGD1 gene have been associated with a rare X-linked disorder known as faciogenital dysplasia (FGDY). Malformations are consistent with a loss of cellular migration during embryonic development. Insertion and deletion mutations in FGD1 result in a frameshift causing inactivation of fgd1 protein. Since Cdc42 is a key molecular switch in cytoskeletal restructuring and cell adhesion, the loss of fgd1 is postulated to attenuate Cdc42-mediated cellular migration in embryonic development. In metastatic tumors, Cdc42 modulates migration and invasiveness. Fgd1 overexpression has been found in infiltrating and poorly differentiated breast and invasive prostate tumors. Amplification at Xp11.21, the FGD1 gene locus, has been reported in several cancers. Sequencing analyses in numerous types of cancer have found missense mutations in the FGD1 gene in metastatic tumors. FGDY and cancer studies suggest that the germline and somatic changes downregulate or upregulate the FGD1 gene playing a key role in the development of diseases.

A novel FGD1 mutation in a family with Aarskog-Scott syndrome and predominant features of congenital joint contractures

Mutations in FGD1 cause Aarskog-Scott syndrome (AAS), an X-linked condition characterized by abnormal facial, skeletal, and genital development due to abnormal embryonic morphogenesis and skeletal formation. Here we report a novel FGD1 mutation in a family with atypical features of AAS, specifically bilateral upper and lower limb congenital joint contractures and cardiac abnormalities. The male proband and his affected maternal uncle are hemizygous for the novel FGD1 mutation p.Arg921X. This variant is the most carboxy-terminal FGD1 mutation identified in a family with AAS and is predicted to truncate the FGD1 protein at the second to last amino acid of the carboxy-terminal pleckstrin homology (PH) domain. Our study emphasizes the importance of the 3' peptide sequence in the structure and/or function of the FGD1 protein and further demonstrates the need to screen patients with X-linked congenital joint contractures for FGD1 mutations.

Identification of novel mutations in Mexican patients with Aarskog-Scott syndrome

Aarskog-Scott syndrome (AAS), also known as faciogenital dysplasia (FGD, OMIM # 305400), is an X-linked disorder of recessive inheritance, characterized by short stature and facial, skeletal, and urogenital abnormalities. AAS is caused by mutations in the FGD1 gene (Xp11.22), with over 56 different mutations identified to date. We present the clinical and molecular analysis of four unrelated families of Mexican origin with an AAS phenotype, in whom FGD1 sequencing was performed. This analysis identified two stop mutations not previously reported in the literature: p.Gln664* and p.Glu380*. Phenotypically, every male patient met the clinical criteria of the syndrome, whereas discrepancies were found between phenotypes in female patients. Our results identify two novel mutations in FGD1, broadening the spectrum of reported mutations; and provide further delineation of the phenotypic variability previously described in AAS.

Aarskog-Scott syndrome: a novel mutation in the FGD1 gene associated with severe craniofacial dysplasia

Aarskog syndrome (AAS) is an X-linked human disease that affects the skeletal formation and embryonic morphogenesis and is caused by mutations in the FGD1 gene. Patients typically show distinctive skeletal and genital developmental abnormalities, but a broad spectrum of clinical phenotypes has been observed. We report here on the clinical and molecular analysis of a family that reveals a novel FGD1 mutation in a 9-year-old boy displaying extreme craniofacial dysplasia associated with attention deficit hyperactivity disorder. Sequencing of FGD1 revealed a novel mutation in exon 7 at position c.1468 C > T in the index patient, leading to a stop codon in the highly conserved RhoGEF gene domain. His mother and maternal grandmother were also found to be heterozygous for this FGD1 mutation.

CONCLUSION

Our results identify a novel mutation of FDG1 in a family with Aarskog syndrome and underscore the phenotypical variability of this condition.

The Cdc42 guanine nucleotide exchange factor FGD6 coordinates cell polarity and endosomal membrane recycling in osteoclasts

The initial step of bone digestion is the adhesion of osteoclasts onto bone surfaces and the assembly of podosomal belts that segregate the bone-facing ruffled membrane from other membrane domains. During bone digestion, membrane components of the ruffled border also need to be recycled after macropinocytosis of digested bone materials. How osteoclast polarity and membrane recycling are coordinated remains unknown. Here, we show that the Cdc42-guanine nucleotide exchange factor FGD6 coordinates these events through its Src-dependent interaction with different actin-based protein networks. At the plasma membrane, FGD6 couples cell adhesion and actin dynamics by regulating podosome formation through the assembly of complexes comprising the Cdc42-interactor IQGAP1, the Rho GTPase-activating protein ARHGAP10, and the integrin interactors Talin-1/2 or Filamin A. On endosomes and transcytotic vesicles, FGD6 regulates retromer-dependent membrane recycling through its interaction with the actin nucleation-promoting factor WASH. These results provide a mechanism by which a single Cdc42-exchange factor controlling different actin-based processes coordinates cell adhesion, cell polarity, and membrane recycling during bone degradation.

Syndromic disorders with short stature

Short stature is one of the major components of many dysmorphic syndromes. Growth failure may be due to a wide variety of mechanisms, either related to the growth hormone (GH)/insulin-like growth factor axis or to underlying unknown pathologies. In this review, the relatively more frequently seen syndromes with short stature (Noonan syndrome, Prader-Willi syndrome, Silver-Russell syndrome and Aarskog-Scott syndrome) were discussed. These disorders are associated with a number of endocrinopathies, as well as with developmental, systemic and behavioral issues. At present, GH therapy is used in most syndromic disorders, although long-term studies evaluating this treatment are insufficient and some controversies exist with regard to GH dose, optimal age to begin therapy and adverse effects. Before starting GH treatment, patients with syndromic disorders should be evaluated extensively.

Exome sequencing identifies a branch point variant in Aarskog-Scott syndrome

Aarskog-Scott syndrome (ASS) is a rare disorder with characteristic facial, skeletal, and genital abnormalities. Mutations in the FGD1 gene (Xp11.21) are responsible for ASS. However, mutation detection rates are low. Here, we report a family with ASS where conventional Sanger sequencing failed to detect a pathogenic change in FGD1. To identify the causative gene, we performed whole-exome sequencing in two patients. An initial analysis did not reveal a likely candidate gene. After relaxing our filtering criteria, accepting larger intronic segments, we unexpectedly identified a branch point (BP) variant in FGD1. Analysis of patient-derived RNA showed complete skipping of exon 13, leading to premature translation termination. The BP variant detected is one of very few reported so far proven to affect splicing. Our results show that besides digging deeper to reveal nonobvious variants, isolation and analysis of RNA provides a valuable but under-appreciated tool to resolve cases with unknown genetic defects.

MLK3 regulates bone development downstream of the faciogenital dysplasia protein FGD1 in mice

Mutations in human FYVE, RhoGEF, and PH domain-containing 1 (FGD1) cause faciogenital dysplasia (FGDY; also known as Aarskog syndrome), an X-linked disorder that affects multiple skeletal structures. FGD1 encodes a guanine nucleotide exchange factor (GEF) that specifically activates the Rho GTPase CDC42. However, the mechanisms by which mutations in FGD1 affect skeletal development are unknown. Here, we describe what we believe to be a novel signaling pathway in osteoblasts initiated by FGD1 that involves the MAP3K mixed-lineage kinase 3 (MLK3). We observed that MLK3 functions downstream of FGD1 to regulate ERK and p38 MAPK, which in turn phosphorylate and activate the master regulator of osteoblast differentiation, Runx2. Mutations in FGD1 found in individuals with FGDY ablated its ability to activate MLK3. Consistent with our description of this pathway and the phenotype of patients with FGD1 mutations, mice with a targeted deletion of Mlk3 displayed multiple skeletal defects, including dental abnormalities, deficient calvarial mineralization, and reduced bone mass. Furthermore, mice with knockin of a mutant Mlk3 allele that is resistant to activation by FGD1/CDC42 displayed similar skeletal defects, demonstrating that activation of MLK3 specifically by FGD1/CDC42 is important for skeletal mineralization. Thus, our results provide a putative biochemical mechanism for the skeletal defects in human FGDY and suggest that modulating MAPK signaling may benefit these patients.

Podosomal proteins as causes of human syndromes: a role in craniofacial development?

Podosomes and invadopodia are actin-rich protrusions of the plasma membrane important for matrix degradation and cell migration. Most of the information in this field has been obtained in cancer cells, where the presence of invadopodia has been related to increased invasiveness and metastatic potential. The importance of the related podosome structure in other pathological or physiological processes that require cell invasion is relatively unexplored. Recent evidence indicates that essential components of podosomes are responsible for several human syndromes, some of which are characterized by serious developmental defects involving the craniofacial area, skeleton and heart, and very poor prognosis. Here we will review them and discuss the possible role of podosomes as a player in correct embryo development.

Familial syndrome resembling Aarskog syndrome

Aarskog(-Scott) syndrome (AAS) is characterized by short stature, and facial, limb, and genital anomalies. AAS can be an X-linked condition caused by mutations in the FGD1 gene, but there is evidence that an autosomal dominant or recessive form also exists. We report on a Chinese family in whom several members have manifestations of AAS, but differ in limb anomalies and show additional characteristics. FGD1 sequencing and linkage analysis excluded FGD1 as the cause in this family. A common known submicroscopic chromosome imbalance is less likely. Both autosomal dominant and recessive patterns of inheritance remain possible.

Proline-rich domain plays a crucial role in extracellular stimuli-responsive translocation of a Cdc42 guanine nucleotide exchange factor, FGD1

We previously demonstrated that FGD1, the Cdc42 guanine nucleotide exchange factor (GEF) responsible for faciogenital dysplasia, and its homologue FGD3 are targeted by the ubiquitin ligase SCF(FWD1) upon phosphorylation of two serine residues in their DSGIDS motif and subsequently degraded by the proteasome. FGD1 and FGD3 share highly homologous Dbl homology (DH) and adjacent pleckstrin homology (PH) domains, both of which are responsible for GEF activity. However, their function and regulation are remarkably different. Here we demonstrate extracellular signal-responsive translocation of FGD1, but not FGD3. During the wound-healing process, translocation of FGD1 to the leading edge membrane occurs in cells facing to the wound. Furthermore, epidermal growth factor (EGF) stimulates the membrane translocation of FGD1, but not FGD3. As the most striking difference, FGD3 lacks the N-terminal proline-rich domain that is conserved in FGD1, indicating that proline-rich domain may play a crucial role in signal-responsive translocation of FGD1. Indeed, there is a faciogenital dysplasia patient who has a missense mutation in proline-rich domain of FGD1, by which the serine residue at position 205 is substituted with isoleucine. When expressed in cells, the mutant FGD1 with S(205)/I substitution fails to translocate to the membrane in response to the mitogenic stimuli. Thus we present a novel mechanism by which the activity of FGD1, a GEF for Cdc42, is temporally and spatially regulated in cells.

Evolutionary genomics of human intellectual disability

Previous studies have postulated that X-linked and autosomal genes underlying human intellectual disability may have also mediated the evolution of human cognition. We have conducted the first comprehensive assessment of the extent and patterns of positive Darwinian selection on intellectual disability genes in humans. We report three main findings. First, as noted in some previous reports, intellectual disability genes with primary functions in the central nervous system exhibit a significant concentration to the X chromosome. Second, there was no evidence for a higher incidence of recent positive selection on X-linked than autosomal intellectual disability genes, nor was there a higher incidence of selection on such genes overall, compared to sets of control genes. However, the X-linked intellectual disability genes inferred to be subject to recent positive selection were concentrated in the Rho GTP-ase pathway, a key signaling pathway in neural development and function. Third, among all intellectual disability genes, there was evidence for a higher incidence of recent positive selection on genes involved in DNA repair, but not for genes involved in other functions. These results provide evidence that alterations to genes in the Rho GTP-ase and DNA-repair pathways may play especially-important roles in the evolution of human cognition and vulnerability to genetically-based intellectual disability.

Bilateral anterior hip dislocation in a child with Aarskog syndrome: a case report

Both Aarskog syndrome and atraumatic anterior hip dislocation are rare entities. Aarskog syndrome is an X-linked recessive disorder with facial, digital, and genital anomalies and is associated with varying degrees of ligamentous laxity. This is believed to be the only known reported case of bilateral anterior voluntary dislocating hips in an ambulatory child and the only reported case of hip dislocation in a child with Aarskog syndrome. Staged bilateral varus derotational femoral osteotomies and Dega osteotomies were successfully performed. Hardware was removed 1 year after the second operation. The patient has been asymptomatic at 2 years' follow-up. This article calls attention to the features of Aarskog syndrome and potential orthopaedic concerns.

A newly recognized craniosynostosis syndrome with features of Aarskog-Scott and Teebi syndromes

We present two unrelated boys with craniosynostosis and similar facial features including hypertelorism, down-slanted palpebral fissures, ptosis, broad mouth with a thin upper lip, and preauricular pits. Both patients had short, broad first digits as well as short, broad hands. Both also had respiratory difficulties and umbilical abnormalities. Although, many of these features are seen in Aarskog-Scott and in Teebi hypertelorism syndromes, both children had craniosynostosis, which has not been previously reported in either syndrome. We propose that these children may have a previously unreported syndrome consistent with X-linked inheritance, although an autosomal dominant mode of transmission cannot be excluded.

DEHP, bis(2)-ethylhexyl phthalate, alters gene expression in human cells: possible correlation with initiation of fetal developmental abnormalities

Diethylhexylphthalate (DEHP) is a widely distributed phthalate, to which humans are exposed to due to its variety of commercial and manufacturing uses. As a plasticiser, it is found in a wide number of products, and metabolites of DEHP have been detected in urine samples from a high percentage of the people screened for phthalates. We utilised DNA microarray analysis to evaluate DEHP for gene expression disrupting activity using the human cell line MCF-7, and found that DEHP significantly dysregulated approximately 34% of the 2400 genes spotted on the NEN2400 chip we used. The results suggest that DEHP, a known estrogen agonist and probable androgen antagonist, alters the expression of a number of genes, many of which are critical for fetal development. Down-regulation of two genes, FGD1 and PAFAH1B1, related in that both are essential for fetal brain development, was corroborated using quantitative real time PCR. These studies show DEHP to be a highly effective human gene expression-altering chemical, and that, at appropriate concentrations, it has the possibility of altering fetal central nervous system development, resulting in the birth defects lissencephaly and/or faciodigitogenital dysplasia.

Female counterpart of shawl scrotum in Aarskog-Scott syndrome

Aarskog-Scott syndrome (ASS) is an X-linked disorder characterized by facial, skeletal and genital anomalies, including penoscrotal transposition in males. We report on a girl from a family with ASS who exhibits a transposition of the clitoris.