SHOX at a glance: from gene to protein

Shortened fetal long bones: A notable intrauterine phenotypic feature in SHOX-associated skeletal dysplasia

OBJECTIVE

To explore the intrauterine phenotypic spectrum of short stature homeobox-containing (SHOX) gene-associated skeletal dysplasia and provide genetic counseling at-risk pregnancies.

METHOD

We analyzed the fetuses with SHOX-microdeletions identified by single nucleotide polymorphism (SNP)-array. The intrauterine phenotypes and outcomes were further elaborated.

RESULTS

Nine fetuses carrying a single SHOX-microdeletion were reported, with deletion sizes ranging from 0.134 to 1.35 Mb. Shortened long bones were observed in all fetuses, varying from -2.0 standard deviation (SD) to -5.3 SD. Moreover, all cases had a femur length/foot ratio less than 0.87 and a femur/abdominal circumference ratio greater than 0.16, suggesting that non-lethal skeletal dysplasia may be involved. Two fetuses showed intrauterine growth restriction, and two had nasal bone hypoplasia. Prenatal ultrasonography did not reveal other obvious anomalies, including the Madelung deformity. Five microdeletions were inherited and one was de novo. Five terminations and four newborns were recorded. Two newborns had normal stature, and two were short-statured (height <3rd percentile), with one having inflexible wrists.

CONCLUSIONS

SHOX haploinsufficiency may manifest with shortened fetal long bones. The combination of history taking, prenatal ultrasonography, and SNP-array can prompt early prenatal diagnosis and timely postnatal treatment of SHOX-associated skeletal dysplasia.

X chromosome dosage and the genetic impact across human tissues

BACKGROUND

Sex chromosome aneuploidies (SCAs) give rise to a broad range of phenotypic traits and diseases. Previous studies based on peripheral blood samples have suggested the presence of ripple effects, caused by altered X chromosome number, affecting the methylome and transcriptome. Whether these alterations can be connected to disease-specific tissues, and thereby having clinical implication for the phenotype, remains to be elucidated.

METHODS

We performed a comprehensive analysis of X chromosome number on the transcriptome and methylome in blood, fat, and muscle tissue from individuals with 45,X, 46,XX, 46,XY, and 47,XXY.

RESULTS

X chromosome number affected the transcriptome and methylome globally across all chromosomes in a tissue-specific manner. Furthermore, 45,X and 47,XXY demonstrated a divergent pattern of gene expression and methylation, with overall gene downregulation and hypomethylation in 45,X and gene upregulation and hypermethylation in 47,XXY. In fat and muscle, a pronounced effect of sex was observed. We identified X chromosomal genes with an expression pattern different from what would be expected based on the number of X and Y chromosomes. Our data also indicate a regulatory function of Y chromosomal genes on X chromosomal genes. Fourteen X chromosomal genes were downregulated in 45,X and upregulated in 47,XXY, respectively, in all three tissues (AKAP17A, CD99, DHRSX, EIF2S3, GTPBP6, JPX, KDM6A, PP2R3B, PUDP, SLC25A6, TSIX, XIST, ZBED1, ZFX). These genes may be central in the epigenetic and genomic regulation of sex chromosome aneuploidies.

CONCLUSION

We highlight a tissue-specific and complex effect of X chromosome number on the transcriptome and methylome, elucidating both shared and non-shared gene-regulatory mechanism between SCAs.

Screening of the SHOX/PAR1 region using MLPA and miRNA expression profiling in a group of Egyptian children with non-syndromic short stature

Background

Short stature is defined as a body height below the third percentile, based on chronological age, or 2 standard deviations (SD) below the national height standard. The prevalence of short stature is around 2% of children worldwide. Several gene deficiencies have been associated with the etiology of short stature. The SHOX is an important candidate gene for short stature, as its haploinsufficiency underlies syndromic and non-syndromic short stature. Partial and complete duplications of SHOX have been reported in patients with short stature. Proper genetic diagnosis of these children allows for appropriate therapeutic approaches to be administered. Since copy number variation (CNV) is a possible mechanism of interhuman variability and pathogenic disease, the multiplex ligation-dependent probe amplification technique (MLPA) can be used as an initial screening technique. Cartilage tissue expresses specific microRNAs (miRNAs), which play an essential role in the regulation of chondrocyte proliferation and differentiation during growth plate development. We aimed to assess the SHOX/PAR1 region using CNV profiling for non-syndromic short stature in Egyptian children with and without growth hormone deficiency using the MLPA technique and expression profiling of miR-1, miR-15a, and miR-140 using quantitative real-time polymerase chain reaction (qRT-PCR) in a group of Egyptian children with non-syndromic short stature.

Results

Of the fifty cases included in this study, different CNVs were detected in ten children (20%), in/outside the SHOX region. Moreover, in children with short stature, the expression level of miRNA-140 was significantly different from that of healthy controls.

Conclusions

This is one of the first studies that have assessed CNVs in the SHOX/PAR1 region in a group of Egyptian children with short stature. MLPA analysis of SHOX/PAR1 identified different CNVs in children with non-syndromic short stature, suggesting that the MLPA should be used as an initial screening technique in short children, as proper genetic diagnosis of these children leads to implementation of the appropriate therapeutic approach. Alterations in the levels of miRNA-140 in children with short stature suggest that changes in the expression levels of this miRNA are associated with the pathogenesis of short stature.

Applying circulating tumor DNA methylation in the diagnosis of lung cancer

Lung cancer is the leading cause of cancer-related deaths worldwide. Low dose computed tomography (LDCT) is commonly used for disease screening, with identified candidate cancerous regions further diagnosed using tissue biopsy. However, existing techniques are all invasive and unavoidably cause multiple complications. In contrast, liquid biopsy is a noninvasive, ideal surrogate for tissue biopsy that can identify circulating tumor DNA (ctDNA) containing tumorigenic signatures. It has been successfully implemented to assist treatment decisions and disease outcome prediction. ctDNA methylation, a type of lipid biopsy that profiles critical epigenetic alterations occurring during carcinogenesis, has gained increasing attention. Indeed, aberrant ctDNA methylation occurs at early stages in lung malignancy and therefore can be used as an alternative for the early diagnosis of lung cancer. In this review, we give a brief synopsis of the biological basis and detecting techniques of ctDNA methylation. We then summarize the latest progress in use of ctDNA methylation as a diagnosis biomarker. Lastly, we discuss the major issues that limit application of ctDNA methylation in the clinic, and propose possible solutions to enhance its usage.

Retinoic acid catabolizing enzyme CYP26C1 is a genetic modifier in SHOX deficiency

Mutations in the homeobox gene SHOX cause SHOX deficiency, a condition with clinical manifestations ranging from short stature without dysmorphic signs to severe mesomelic skeletal dysplasia. In rare cases, individuals with SHOX deficiency are asymptomatic. To elucidate the factors that modify disease severity/penetrance, we studied a three-generation family with SHOX deficiency. The variant p.Phe508Cys of the retinoic acid catabolizing enzyme CYP26C1 co-segregated with the SHOX variant p.Val161Ala in the affected individuals, while the SHOX mutant alone was present in asymptomatic individuals. Two further cases with SHOX deficiency and damaging CYP26C1 variants were identified in a cohort of 68 individuals with LWD The identified CYP26C1 variants affected its catabolic activity, leading to an increased level of retinoic acid. High levels of retinoic acid significantly decrease SHOX expression in human primary chondrocytes and zebrafish embryos. Individual morpholino knockdown of either gene shortens the pectoral fins, whereas depletion of both genes leads to a more severe phenotype. Together, our findings describe CYP26C1 as the first genetic modifier for SHOX deficiency.

Epigenetic Dysfunction in Turner Syndrome Immune Cells

Turner syndrome (TS) is a chromosomal condition associated with partial or complete absence of the X chromosome that involves characteristic findings in multiple organ systems. In addition to well-known clinical characteristics such as short stature and gonadal failure, TS is also associated with T cell immune alterations and chronic otitis media, suggestive of a possible immune deficiency. Recently, ubiquitously transcribed tetratricopeptide repeat on the X chromosome (UTX), a histone H3 lysine 27 (H3K27) demethylase, has been identified as a downregulated gene in TS immune cells. Importantly, UTX is an X-linked gene that escapes X-chromosome inactivation and thus is haploinsufficient in TS. Mice with T cell-specific UTX deficiency have impaired clearance of chronic viral infection due to decreased frequencies of T follicular helper (Tfh) cells, which are critical for B cell antibody generation. In parallel, TS patients have decreased Tfh frequencies in peripheral blood. Together, these findings suggest that haploinsufficiency of the X-linked UTX gene in TS T cells underlies an immune deficit, which may manifest as increased predisposition to chronic otitis media.

A Track Record on SHOX: From Basic Research to Complex Models and Therapy

SHOX deficiency is the most frequent genetic growth disorder associated with isolated and syndromic forms of short stature. Caused by mutations in the homeobox gene SHOX, its varied clinical manifestations include isolated short stature, Léri-Weill dyschondrosteosis, and Langer mesomelic dysplasia. In addition, SHOX deficiency contributes to the skeletal features in Turner syndrome. Causative SHOX mutations have allowed downstream pathology to be linked to defined molecular lesions. Expression levels of SHOX are tightly regulated, and almost half of the pathogenic mutations have affected enhancers. Clinical severity of SHOX deficiency varies between genders and ranges from normal stature to profound mesomelic skeletal dysplasia. Treatment options for children with SHOX deficiency are available. Two decades of research support the concept of SHOX as a transcription factor that integrates diverse aspects of bone development, growth plate biology, and apoptosis. Due to its absence in mouse, the animal models of choice have become chicken and zebrafish. These models, therefore, together with micromass cultures and primary cell lines, have been used to address SHOX function. Pathway and network analyses have identified interactors, target genes, and regulators. Here, we summarize recent data and give insight into the critical molecular and cellular functions of SHOX in the etiopathogenesis of short stature and limb development.

Short Stature in Isodicentric Y Chromosome and Three Copies of the SHOX Gene: Clinical Report and Review of Literature

Short stature homeobox gene (SHOX) mutations and pseudoautosomal region 1 (PAR1) deletions encompassing SHOX are known causes of Léri-Weill dyschondrosteosis and isolated short stature, while 3 copies of SHOX in cases with triple sex chromosome constitution are responsible for tall stature. Duplications involving SHOX have been rarely reported, and they were found in individuals with short, normal and tall stature. An adopted boy with short stature, isodicentric Y chromosome and 3 copies of SHOX is described. Normal growth hormone (GH) secretion and insulin-like growth factor 1 (IGF1) increase during an IGF1 generation test were found, ruling out impaired GH-IGF1 axis. No other organic or psychiatric causes of impaired growth were found. GH treatment improved linear growth, as reported in children with SHOX haploinsufficiency. This new report and the review of literature support that SHOX duplication may cause short stature, especially in those children with duplications of the 5'SHOX regulatory elements. Chromosome analysis and detailed molecular characterization of the duplicated region should be warranted in individuals with SHOX duplications in order to investigate the presence of occult chromosome imbalance. Additional reports and follow-up till adult height are needed to give conclusions on long-term efficacy and safety of GH treatment in short children with SHOX duplication.

Systematic molecular analyses of SHOX in Japanese patients with idiopathic short stature and Leri-Weill dyschondrosteosis

The etiology of idiopathic short stature (ISS) and Leri-Weill dyschondrosteosis (LWD) in European patients is known to include SHOX mutations and copy-number variations (CNVs) involving SHOX and/or the highly evolutionarily conserved non-coding DNA elements (CNEs) flanking the gene. However, the frequency and types of SHOX abnormalities in non-European patients and the clinical importance of mutations in the CNEs remains to be clarified. Here, we performed systematic molecular analyses of SHOX for 328 Japanese patients with ISS or LWD. SHOX abnormalities accounted for 3.8% of ISS and 50% of LWD cases. CNVs around SHOX were identified in 16 cases, although the ~47 kb deletion frequently reported in European patients was absent in our cases. Probably damaging mutations and benign/silent substitutions were detected in four cases, respectively. Although CNE-linked substitutions were detected in 15 cases, most of them affected poorly conserved nucleotides and were shared by unaffected individuals. These results suggest that the frequency and mutation spectrum of SHOX abnormalities are comparable between Asian and European patients, with the exception of a European-specific downstream deletion. Furthermore, this study highlights the clinical importance and genetic heterogeneity of the SHOX-flanking CNVs, and indicates a limited clinical significance of point mutations in the CNEs.

SHOX gene variants: growth hormone/insulin-like growth factor-1 status and response to growth hormone treatment

CONTEXT

Short stature homeobox-containing gene (SHOX) variants of unknown clinical significance occur frequently among children with short stature, yet their growth hormone (GH)/insulin-like growth factor-1 (IGF-1) status and response to GH have not been studied.

OBJECTIVE

To define GH and IGF-1 status in children with SHOX variants and assess their response to GH.

PATIENTS AND METHODS

This is a retrospective review of children with short stature. Children with SHOX variants were compared to those with no variants. Height standard deviation scores (SDS) and IGF-1 SDS at baseline and during GH treatment at 6, 12, and 24 months were analyzed. Growth velocity (GV), maximum GH dose, IGF-BP3, and changes in height SDS, IGF-1 SDS, and GV were compared.

RESULTS

Among 355 children, 83 (23%) had SHOX variants. Nineteen different SHOX variants were detected. There was no difference in age, height SDS, IGF-1 SDS, or IGF-BP3 between children with SHOX variants and those with normal SHOX. Height SDS, IGF-1 SDS, IGF-BP3, GV, and GH dose were not different between patients with SHOX variants and those without.

CONCLUSIONS

The GH and IGF-1 characteristics of children with short stature were not different between children with SHOX+ variants and children with no variants. Although these findings suggest that SHOX variants are polymorphisms, studies prospectively comparing individual SHOX variants are needed.

Alu-mediated recombination defect in IGF1R: haploinsufficiency in a patient with short stature

BACKGROUND

The insulin-like growth factor (IGF) receptor (IGF1R) is essential for normal development and growth. IGF1R mutations cause IGF-1 resistance resulting in intrauterine and postnatal growth failure. The phenotypic spectrum related to IGF1R mutations remains to be fully understood.

METHODS

Auxological and endocrinological data of a patient identified previously were assessed. The patient's fibroblasts were studied to characterize the IGF1R deletion, mRNA fate, protein expression and signalling capabilities.

RESULTS

The boy, who carries a heterozygous IGF1R exon 6 deletion caused by Alu element-mediated recombination and a heterozygous SHOX variant (p.Met240Ile), was born appropriate for gestational age but developed proportionate short stature postnatally. IGF-1 levels were low-normal. None of the stigmata associated with SHOX deficiency or sporadically observed in IGF1R mutation carriers were present. Nonsense-mediated mRNA decay led to a substantial decline of IGF1R dosage and IGF-1-dependent receptor autophosphorylation but not impaired downstream signalling.

CONCLUSION

We present the first detailed report of an intragenic IGF1R deletion identified in a patient who, apart from short stature, deviates from all established markers that qualify a growth-retarded child for IGF1R analysis. Although such children will usually escape routine clinical mutation screenings, they can contribute to the understanding of factors and mechanisms that cooperate with the IGF1R.

Rare inheritance of Leri-Weill Syndrome due to crossover of short stature Homeobox Gene (SHOX) Deletions between X and Y Chromosomes: a case report

Background

Leri-Weill syndrome (LWS) is a genetic disorder caused by deletions or mutations in the SHOX gene or by deletions downstream of the gene and is classically characterized by short stature, mesomelic shortening of forearms and legs, and Madelung deformity. Correct identification of short stature homeobox-containing gene (SHOX) deficiency in children with growth problems is vital for appropriate initiation of growth hormone therapy.

Method

We report a phenotypically normal 23 day old male infant born to a father diagnosed with Leri-Weill syndrome at age 12 years with a documented SHOX deletion on his X chromosome. The patient’s fetal long bones had been found to be about three weeks delayed in growth on prenatal ultrasound during the second trimester.

Results

The infant underwent genetic evaluation at 23 days of life and was found to have a SHOX deletion on Yp11.32 identified using single nucleotide polymorphism microarray (SNP) analysis and confirmed by FISH using a SHOX gene probe.

Conclusion

We report the case of a male infant diagnosed with Leri-Weill syndrome with an unusual documented inheritance between father and son due to crossover between X and Y chromosomes during paternal meiosis. Our case is the youngest patient in literature documented by FISH analysis to have an X to Y chromosome transfer and the first of these patients diagnosed prior to onset of short stature or Madelung deformity. Our patient was identified prior to growth failure and can now be monitored for growth abnormalities with the ability to implement growth augmentation therapy without delay. Our case highlights the importance of advising affected SHOX patients of risks to future offspring and supports screening off-spring of parents carrying SHOX abnormalities regardless of sex.

SHOX triggers the lysosomal pathway of apoptosis via oxidative stress

The SHOX gene encodes for a transcription factor important for normal bone development. Mutations in the gene are associated with idiopathic short stature and are responsible for the growth failure and skeletal defects found in the majority of patients with Léri-Weill dyschondrosteosis (LWD) and Langer mesomelic dysplasia. SHOX is expressed in growth plate chondrocytes where it is supposed to modulate the proliferation, differentiation and cell death of these cells. Supporting this hypothesis, in vitro studies have shown that SHOX expression induces cell cycle arrest and apoptosis in both transformed and primary cells. In this study, we further characterized the cell death mechanisms triggered by SHOX and compared them with the effects induced by one clinically relevant mutant form of SHOX, detected in LWD patients (SHOX R153L) and a SHOX C-terminally truncated version (L185X). We show that SHOX expression in U2OS osteosarcoma cells leads to oxidative stress that, in turn, induces lysosomal membrane rupture with release of active cathepsin B to the cytosol and subsequent activation of the intrinsic apoptotic pathway characterized by mitochondrial membrane permeabilization and caspase activation. Importantly, cells expressing SHOX R153L or L185X did not display any of these features. Given the fact that many of the events observed in SHOX-expressing cells also characterize the complex cell death process occurring in the growth plate during endochondral ossification, our findings further support the hypothesis that SHOX may play a central role in the regulation of the cell death pathways activated during long bone development.

All Madelung deformities are not endocrine

Madelung deformity is a rare inherited disorder associated with endocrine disorders like Turner's syndrome, pseudohypoparathyroidism, but can be seen with short stature homeobox deficiency conditions such as Leri-Weill dyschondrosteosis (LWD) and Langers mesomelic dysplasia. It has also been reported following trauma to the distal radius epiphysis neoplasia mucopolysaccharidosis (MPS) and achondroplasia. Madelung deformity is an abnormality of distal radial epiphysis where in progressive ulnar and volar tilt of the articular surface occurring in association with distal subluxation of ulna. A 13-year-old girl was referred to us for evaluation of bilateral deformity of wrist and short stature. There was ulnar deviation and dorsal tilt of bilateral hands without history of pain to the joint trauma and family history of similar illness. On X-ray, wrist showed malformed distal radial epiphysis with dorsal and ulnar shift and with increased length of phalanges suggestive of Madelung deformity. X-ray spine was normal. Ultrasound abdomen showed normal uterus and ovary and her follicle stimulating hormone. Luteinizing hormone was normal and so was urine MPS screening. Based on the above points the diagnosis of LWD was made.

DNA methylation of the homeobox genes PITX2 and SHOX2 predicts outcome in non-small-cell lung cancer patients

Biomarkers that facilitate prediction of disease progression in lung cancer patients might be clinically valuable in optimizing individualized therapy. In this study, the ability of the DNA methylation biomarkers PITX2 and SHOX2 to predict disease outcome in lung cancer patients has been evaluated. Quantitative, methylation-specific (HeavyMethyl), real-time polymerase chain reaction assays were used to measure DNA methylation of PITX2 and SHOX2 in bisulfite-converted DNA from formalin-fixed, paraffin-embedded tissues from 474 non-small-cell lung cancer patients. In univariate Cox Proportional Hazard analysis, high methylation of SHOX2 and PITX2 was a significant predictor of progression-free survival [SHOX2: n=465, hazard ratio (HR)=1.395 (1.130 to 1.721), P=0.002; PITX2: n=445, HR=1.312 (1.059 to 1.625), P=0.013]. Patients with low methylation of either PITX2 and/or SHOX2 (n=319) showed a significantly higher risk of disease progression as compared with patients with higher methylation of both genes [n=126; HR=1.555 (1.210 to 1.999), P=0.001]. This was particularly true for the subgroup of patients receiving no adjuvant radiotherapy or chemotherapy [n=258, HR=1.838 (1.252 to 2.698), P=0.002]. In multivariate analysis, both biomarkers added significant independent prognostic information to pT, pN, pM, and grade. Another interesting finding of this study was that SHOX2 and PITX2 DNA methylation was shown to be inversely correlated with TTF1 (also known as NKX2-1) expression (PITX2: P=0.018, SHOX2: P<0.001). TFF1 expression was previously found to be associated with improved survival in the same patient cohort. DNA methylation of PITX2 and SHOX2 is an independent prognostic biomarker for disease progression in non-small-cell lung cancer patients.

Shox2 regulates progression through chondrogenesis in the mouse proximal limb

In humans, loss of SHOX gene function is responsible for the mesomelic short stature characteristic of Turner syndrome, Leri-Weill dyschondrosteosis, and Langer dysplasia. In a mouse model of SHOX deficiency, Prrx1-Cre-driven limb-specific deletion of the paralogous gene Shox2 results in severe rhizomelia. In this study, we show that Col2a1-Cre-driven deletion of Shox2 in developing chondrocytes also results in shortening of the stylopodial skeleton (i.e. humerus, femur) and that this rhizomelia is due to precocious chondrocyte maturation and hypertrophy. We demonstrate, using the micromass culture model system, that increased BMP activity triggers accelerated maturation and hypertrophy in Col2a1-Cre Shox2 mutant chondrocytes and we confirm in vivo that elevated transcript levels and expanded expression domains of Bmp2 and 4 are associated with premature formation of the hypertrophic zone in mutant humeri. In micromass cultures of Prrx1-Cre Shox2 mutant limb cells, we find that Shox2 deletion in undifferentiated mesenchymal cells results in increased BMP activity that enhances early chondrogenesis, but is insufficient to provoke chondrocyte maturation and hypertrophy. Similarly, shRNA-mediated Shox2 knockdown in multipotent C3H10T1/2 cells and primary mouse bone marrow mesenchymal stem cells results in spontaneous chondrogenesis in the absence of chondrostimulation, but again fails to induce progression through the later stages of chondrogenic differentiation. Importantly, exogenous BMP supplementation can overcome the block to maturation and hypertrophy caused by Shox2 depletion prior to overt chondrogenesis. Thus, we provide evidence that Shox2 regulates progression through chondrogenesis at two distinct stages – the onset of early differentiation and the transition to maturation and hypertrophy.

A novel intronic mutation in SHOX causes short stature by disrupting a splice acceptor site: direct demonstration of aberrant splicing by expression of a minigene in HEK-293T cells

SHOX, the short stature homeobox-containing gene, encodes a critical regulatory protein controlling long bone growth. We examined patients in one family, identified an intronic mutation, and expressed SHOX minigenes in HEK293T cells to characterize the effect on gene splicing. We identified a novel mutation at position -3 (c.-432-3C>A;g.6120C>A) of the intron 1 splice acceptor site; three short (height Z-score -2.4 to -1.7) children were heterozygous and the father (height Z-score -3.4) was homozygous. A wild-type minigene produced alternative transcripts; one utilized the normal splice site between intron 1 and exon 2, the other a cryptic splice site in exon 2. Mutant SHOX minigene generated only the smaller transcript. The exon 2 acceptor splice site is weak; an alternative transcript is normally produced using a downstream cryptic splice site. The c.-432-3C>A mutation causes further weakening, and the cryptic splice site is preferentially utilized, resulting in SHOX deficiency and short stature.

Transcription factor short stature homeobox 2 is required for proper development of tropomyosin-related kinase B-expressing mechanosensory neurons

Dorsal root ganglia (DRG) contain somatosensory neurons of diverse sensory modalities. Among these different types of sensory neurons, the molecular mechanisms that regulate the development and specification of touch neurons are the least well understood. We took a candidate approach and searched for transcription factors that are expressed in subsets of DRG neurons, and found that the transcription factor Shox2 (short stature homeobox 2) is expressed in subpopulations of TrkB (tropomyosin-related kinase B)- and Ret-expressing neurons at neonatal stages. Since TrkB is a known marker that is selectively expressed in touch sensory neurons, we decided to examine the function of Shox2 in specifying TrkB-positive DRG neurons. Conditional deletion of Shox2 in neural crest cells (which give rise to all DRG neurons) caused a 60 ∼ 65% reduction in the number of TrkB-expressing neurons. It also resulted in an increase in coexpression of TrkC in Ret-positive sensory neurons. Deletion of Shox2 in differentiating DRG neurons at later time points caused only a moderate reduction in TrkB expression. Overexpression of Shox2 in all neural crest cells resulted in a small increase in the number of TrkB-expressing neurons. Finally, Shox2 deletion also caused reduced touch sensory axonal innervation to layers III/IV of the spinal cord. Together, our findings identify Shox2 as an essential but not sufficient component of the transcription programs required in neural progenitor cells for the proper specification of subsets of TrkB-expressing touch/mechanosensory neurons.

Correlation of SHOX2 gene amplification and DNA methylation in lung cancer tumors

BACKGROUND

DNA methylation in the SHOX2 locus was previously used to reliably detect lung cancer in a group of critical controls, including 'cytologically negative' samples with no visible tumor cell content, at a high specificity based on the analysis of bronchial lavage samples. This study aimed to investigate, if the methylation correlates with SHOX2 gene expression and/or copy number alterations. An amplification of the SHOX2 gene locus together with the observed tumor-specific hypermethylation might explain the good performance of this marker in bronchial lavage samples.

METHODS

SHOX2 expression, gene copy number and DNA methylation were determined in lung tumor tissues and matched morphologically normal adjacent tissues (NAT) from 55 lung cancer patients. Quantitative HeavyMethyl (HM) real-time PCR was used to detect SHOX2 DNA methylation levels. SHOX2 expression was assayed with quantitative real-time PCR, and copy numbers alterations were measured with conventional real-time PCR and array CGH.

RESULTS

A hypermethylation of the SHOX2 locus in tumor tissue as compared to the matched NAT from the same patient was detected in 96% of tumors from a group of 55 lung cancer patients. This correlated highly significantly with the frequent occurrence of copy number amplification (p < 0.0001), while the expression of the SHOX2 gene showed no difference.

CONCLUSIONS

Frequent gene amplification correlated with hypermethylation of the SHOX2 gene locus. This concerted effect qualifies SHOX2 DNA methylation as a biomarker for lung cancer diagnosis, especially when sensitive detection is needed, i.e. in bronchial lavage or blood samples.

Vitamin D receptor genotypes are associated with bone mass in patients with Turner syndrome

BACKGROUND

Turner syndrome (TS) patients present low bone mineral density (BMD) and increased fracture risk, probably due to a genetic defect aggravated by hormonal deficiency.

AIM

To study the relationship between vitamin D receptor (VDR) gene polymorphisms and BMD and bone parameters in TS patients.

METHODS

DNA from 65 TS patients and 110 controls was amplified by PCR and digested with FokI, BsmI and ApaI restrictases. Lumbar and femoral BMD were determined by DEXA and serum intact parathyroid hormone, osteocalcin and beta-CrossLaps by electrochemiluminescence.

RESULTS

Genotype distribution within the ApaI site was different in both groups: genotype Aa was more abundant in TS (63.8% vs. 41.3%; p<0.01), whereas AA predominated in controls (33.9% vs. 15.5%; p<0.01). Patients carrying genotype bb (BsmI) or ff (FokI) had lower BMD than those with other genotypes (p<0.01 and p<0.05, respectively).

CONCLUSION

BsmI and FokI polymorphic sites of VDR could be genetic determinants of BMD in TS patients.

Improved molecular diagnostics of idiopathic short stature and allied disorders: quantitative polymerase chain reaction-based copy number profiling of SHOX and pseudoautosomal region 1

CONTEXT

Short stature has an incidence of three in 100 in children. Reliable molecular genetic testing may be crucial in the context of beneficial disease management. Deletions spanning or surrounding the SHOX gene account for a significant proportion of patients with idiopathic short stature (ISS) and allied disorders, such as Leri-Weill dyschondrosteosis.

OBJECTIVE

Several shortcomings of current strategies for copy number profiling of the SHOX region prompted us to develop an improved test for molecular diagnostics of the SHOX region.

DESIGN AND RESULTS

We introduced a quantitative PCR (qPCR)-based copy number profiling test, consisting of 11 amplicons targeting clinically relevant regions, i.e. the SHOX gene and regulatory regions. To ensure an optimal sensitivity and specificity, this test was validated in 32 controls and 18 probands with previously identified copy number changes. In addition, 152 probands with SHOX-associated phenotypes were screened, revealing 10 novel copy number changes.

CONCLUSION

This highly validated qPCR test supersedes other approaches for copy number screening of the SHOX region in terms of reliability, accuracy, and cost efficiency. In addition, another strong point is the fact that it can be easily implemented in any standard equipped molecular laboratory. Our qPCR-based test is highly recommended for molecular diagnostics of idiopathic short stature and allied disorders.

Approach to the patient with Turner syndrome

Turner syndrome (TS) occurs in about 1:4000 live births and describes females with a broad constellation of problems associated with loss of an entire sex chromosome or a portion of the X chromosome containing the tip of its short arm. TS is associated with an astounding array of potential abnormalities, most of them thought to be caused by haploinsufficiency of genes that are normally expressed by both X chromosomes. A health care checklist is provided that suggests screening tests at specific ages and intervals for problems such as strabismus, hearing loss, and autoimmune thyroid disease. Four areas of major concern in TS are discussed: growth failure, cardiovascular disease, gonadal failure, and learning disabilities. GH therapy should generally begin as soon as growth failure occurs, allowing for rapid normalization of height. Cardiac imaging, preferably magnetic resonance imaging, should be performed at diagnosis and repeated at 5- to 10-yr intervals to assess for congenital heart abnormalities and the emergence of aortic dilatation, a precursor to aortic dissection. Hypertension should be aggressively treated. For those with gonadal dysgenesis, hormonal replacement therapy should begin at a normal pubertal age and be continued until the age of 50 yr. Transdermal estradiol provides the most physiological replacement. Finally, nonverbal learning disabilities marked by deficits in visual-spatial-organizational skills, complex psychomotor skills, and social skills are common in TS. Neuropsychological testing should be routine and families given support in obtaining appropriate therapy, including special accommodations at school.

SHOX gene is expressed in vertebral body growth plates in idiopathic and congenital scoliosis: implications for the etiology of scoliosis in Turner syndrome

Reduced SHOX gene expression has been demonstrated to be associated with all skeletal abnormalities in Turner syndrome, other than scoliosis (and kyphosis). There is evidence to suggest that Turner syndrome scoliosis is clinically and radiologically similar to idiopathic scoliosis, although the phenotypes are dissimilar. This pilot gene expression study used relative quantitative real-time PCR (qRT-PCR) of the SHOX (short stature on X) gene to determine whether it is expressed in vertebral body growth plates in idiopathic and congenital scoliosis. After vertebral growth plate dissection, tissue was examined histologically and RNA was extracted and its integrity was assessed using a Bio-Spec Mini, NanoDrop ND-1000 spectrophotometer and standard denaturing gel electrophoresis. Following cDNA synthesis, gene-specific optimization in a Corbett RotorGene 6000 real-time cycler was followed by qRT-PCR of vertebral tissue. Histological examination of vertebral samples confirmed that only growth plate was analyzed for gene expression. Cycling and melt curves were resolved in triplicate for all samples. SHOX abundance was demonstrated in congenital and idiopathic scoliosis vertebral body growth plates. SHOX expression was 11-fold greater in idiopathic compared to congenital (n = 3) scoliosis (p = 0.027). This study confirmed that SHOX was expressed in vertebral body growth plates, which implies that its expression may also be associated with the scoliosis (and kyphosis) of Turner syndrome. SHOX expression is reduced in Turner syndrome (short stature). In this study, increased SHOX expression was demonstrated in idiopathic scoliosis (tall stature) and congenital scoliosis.

Moving toward an understanding of hormone replacement therapy in adolescent girls: looking through the lens of Turner syndrome

Turner syndrome (TS) is a relatively common disorder of phenotypic females caused by loss of all or part of the second sex chromosome. Most individuals with TS have short stature and gonadal dysgenesis and are at risk for many other medical and learning problems. In the 45,X ovary, germs cells multiply quite normally during fetal development, but there is accelerated atresia of oocytes in the second half of pregnancy that produces gonadal insufficiency by birth. In girls with other karyotypes, especially those mosaic for 45,X/46,XX, gonadal function may be normal or near-normal. In this chapter, management goals for gonadal insufficiency in girls with TS are presented. The effects of estrogen deficiency and its replacement on three specific problems associated with TS-short stature, cardiovascular disease, and developmental differences in brain structure and function-are explored. General guidelines for estrogen replacement therapy using transdermal estrogen, the most physiologic option, are provided and future research goals are outlined.