A novel germ line mutation in SOX9 causes familial campomelic dysplasia and sex reversal

Mutations in the gene SOX9 result in the syndrome of campomelic dysplasia (CD) which includes sex-reversal in 75% of 46,XY affected individuals. These mutations only affect a single allele of SOX9 suggesting a dominant mode of inheritance for this syndrome. Consequently, CD and autosomal sex reversal may result from haploinsufficiency of SOX9. The SOX9 gene maps to the long arm of human chromosome 17 and translocations in this region also result in CD. We report a family in which there were three affected patients, two of whom showed 46,XY sex-reversal. Interestingly, despite all three patients being heterozygous for a familial mutation in SOX9 (Insertion of a cytosine residue at nucleotide position 1096), their gonadal phenotypes varied widely. The proband was found to have 46,XY true hermaphroditism with ambiguous genitalia. The other two sibs were 46,XY and 46,XX, and both had bilateral ovaries with normal female genitalia. The somatic cells in both parents revealed wild-type SOX9 nucleotide sequences. However, mutational analysis of the SOX9 gene in the father's germ cells revealed they were mosaic for mutant and wild-type sequences. This family is particularly informative as it demonstrates that the same SOX9 mutation can produce very different 46,XY gonadal phenotypes. The range of gonadal morphologies observed may be explained by several possible mechanisms such as variable penetrance of the mutation, increased activity of the non-mutant SOX9 allele or stochastic environmental factors. These results also demonstrate that paternal germ cell mosaicism of a mutant SOX9 sequence can result in a CD phenotype amongst his offspring.      

Heterozygous SOX9 Mutations Allowing for Residual DNA‐binding and Transcriptional Activation Lead to the Acampomelic Variant of Campomelic Dysplasia

Campomelic dysplasia is a malformation syndrome with multiple symptoms including characteristic shortness and bowing of the long bones (campomelia). CD, often lethal due to airway malformations, is caused by heterozygous mutations in SOX9, an SRY‐related gene regulating testis and chondrocyte development including expression of many cartilage genes such as type II collagen. Male to female sex reversal occurs in the majority of affected individuals with an XY karyotype. A mild form without campomelia exists, in which sex‐reversal may be also absent. We report here two novel SOX9 missense mutations in a male (c.495C>G; p.His165Gln) and a female (c.337A>G; p.Met113Val) within the DNA‐binding domain leading to non‐lethal acampomelic CD. Functional analyses of mutant proteins demonstrate residual DNA‐binding and transactivation of SOX9‐regulated genes. Combining our data and reports from the literature we postulate a genotype‐phenotype correlation: SOX9 mutations allowing for residual function lead to a mild form of CD in which campomelia and sex reversal may be absent. © 2010 Wiley‐Liss, Inc.     

Evidence to exclude SOX9 as a candidate gene for XY sex reversal without skeletal malformation.

The skeletal malformation syndrome campomelic dysplasia (CMD1) is caused by mutations within the SOX9 gene or chromosomal rearrangement breakpoints outside SOX9. Approximately three quarters of cases of CMD1 in XY subjects show complete or partial sex reversal. As some mutations cause CMD1 alone and others cause CMD1 and sex reversal, it is conceivable that some mutations might cause sex reversal in the absence of CMD1. In this study, we have investigated this possibility by screening the entire coding region of SOX9 in 30 patients with a spectrum of XY sex reversal phenotypes. No mutations were identified, suggesting that SOX9 should not be considered a candidate gene for XY sex reversal without skeletal malformation.     

Two novel translocation breakpoints upstream of SOX9 define borders of the proximal and distal breakpoint cluster region in campomelic dysplasia

The semilethal skeletal malformation syndrome campomelic dysplasia (CD) with or without XY sex reversal is caused by mutations within the SOX9 gene on 17q24.3 or by chromosomal aberrations (translocations, inversions or deletions) with breakpoints outside the SOX9 coding region. The previously published CD translocation breakpoints upstream of SOX9 fall into two clusters: a proximal cluster with breakpoints between 50-300 kb and a distal cluster with breakpoints between 899-932 kb. Here, we present clinical, cytogenetic and molecular data from two novel CD translocation cases. Case 1 with karyotype 46,XY,t(1;17)(q42.1;q24.3) has characteristic symptoms of CD, including mild tibial bowing, cryptorchidism and hypospadias. By standard fluorescence in situ hybridization (FISH) and by high-resolution fiber FISH, the 17q breakpoint was mapped 375 kb from SOX9, defining the centromeric border of the proximal breakpoint cluster region. Case 2 with karyotype 46,X,t(Y;17)(q11.2;q24.3) has the acampomelic form of CD and complete XY sex reversal. By FISH and somatic cell hybrid analysis, the 17q breakpoint was mapped 789 kb from SOX9, defining the telomeric border of the distal breakpoint cluster region. We discuss the structure of the 1 Mb cis-control region upstream of SOX9 and the correlation between the position of the 14 mapped translocation breakpoints with respect to disease severity and XY sex reversal.     

性反转综合征患者SRY、SOX9基因检测

目的探讨性反转综合征发生与性别分化相关基因SRY、SOX9之间的关系。方法分析了4例XX男性性反转及1例XY女性性反转患者临床表现、染色体核型，并采用聚合酶链反应（PCR）对SRY、SOX9基因进行了检测。结果5例性反转中，3例XX男性性反转及1例XY女性性反转患者SRY阳性，1例XX男性性反转患者SRY阴性。5例患者均检测到SOX9基因。结论SRY易位是导致性反转发生的重要原因之一，某些性反转的发生可能与SOX9基因异常有关，SOX9的计量效应关系有待研究。     

Recurrent SOX9 deletion campomelic dysplasia due to somatic mosaicism in the father

Haploinsufficiency of SOX9, a master gene in chondrogenesis and testis development, leads to the semi-lethal skeletal malformation syndrome campomelic dysplasia (CD), with or without XY sex reversal. We report on two children with CD and a phenotypically normal father, a carrier of a somatic mosaic SOX9 deletion. This is the first report of a mosaic deletion of SOX9; few familial CD cases with germline and somatic mutation mosaicism have been described. Our findings confirm the utility of aCGH and indicate that for a more accurate estimate of the recurrence risk for a completely penetrant autosomal dominant disorder, parental somatic mosaicism should be considered in healthy parents.     

Functional characterization of five NR5A1 gene mutations found in patients with 46,XY disorders of sex development

Steroidogenic factor‐1 (SF1), encoded by the NR5A1 gene, is a key regulator of steroidogenesis and reproductive development. NR5A1 mutations described in 46,XY patients with disorders of sex development (DSD) can be associated with a range of conditions of phenotypes; however, the genotype–phenotype correlation remains elusive in many cases. In the present study, we describe the impact of five NR5A1 variants (three novel: p.Arg39Cys, p.Ser32Asn, and p.Lys396Argfs*34; and two previously described: p.Cys65Tyr and p.Cys247*) on protein function, identified in seven patients with 46,XY DSD. In vitro functional analyses demonstrate that NR5A1 mutations impair protein functions and result in the DSD phenotype observed in our patients. Missense mutations in the DNA binding domain and the frameshift mutation p.Lys396Argfs*34 lead to both, markedly affected transactivation assays, and loss of DNA binding, whereas the mutation p.Cys247* retained partial transactivation capacity and the ability to bind a consensus SF1 responsive element. SF1 acts in a dose‐dependent manner and regulates a cascade of genes involved in the sex determination and steroidogenesis, but in most cases reported so far, still lead to a sufficient adrenal steroidogenesis and function, just like in our cases, in which heterozygous mutations are associated to 46,XY DSD with intact adrenal steroid biosynthesis.     

A novel missense mutation in the HMG box region of the SRY gene in a Japanese patient with an XY sex reversal

The sex-determining region of the Y chromosome, the SRY gene, located on the short arm of the Y chromosome, is appreciated as one of the genes that is responsible for directing the process of sex differentiation. To date, 34 different mutations, including 29 missense and nonsense mutations in the SRY gene, have been described in XY female patients. We investigated the molecular basis of the sex reversal in one Japanese XY female patient by determining the nucleotide sequence of the SRY gene, using polymerase chain reaction and direct sequencing. We identified a novel mutation, of the substitution of Tyr for Asn at nucleotide position 87 (N87Y). This Asn residue is located within the DNA-binding high-mobility-group (HMG) motif, which is considered to be the main functional domain of the SRY protein. Further, this amino acid, Asn, is a conserved residue among mammalian SRY genes. These findings indicate that this amino acid substitution may be responsible for the sex reversal in this patient. Received: October 12, 1999 / Accepted: November 4, 1999     

Twenty-six novel EFNB1 mutations in familial and sporadic craniofrontonasal syndrome (CFNS)

Craniofrontonasal syndrome (CFNS) is an X-linked disorder characterized by a more severe manifestation in heterozygous females than in hemizygous males. Heterozygous females have craniofrontonasal dysplasia (CFND) and occasionally extracranial manifestations including midline defects and skeletal abnormalities, whereas hemizygous males show no or only mild features such as hypertelorism and rarely show cleft lip or palate. Mutations in the EFNB1 gene in Xq12 are responsible for familial and sporadic CFNS. The EFNB1 gene encodes ephrin-B1, a transmembrane ligand that also exhibits receptor-like effects. We performed mutation analysis in nine unrelated families and 29 sporadic patients with CFNS. DNA sequencing revealed mutations in 33 (86.8%) cases including 26 distinct novel mutations. A recurrent nonsense mutation, c.196C>T/R66X, was detected in one family and four sporadic patients. The majority of mutations (26/33) were located in exons 2 and 3 of the EFNB1 gene encoding the extracellular ephrin domain. The mutation spectrum includes frameshift, nonsense, missense, and splice site mutations, with a predominance of frameshift and nonsense mutations resulting in premature truncation codons. For the first time we describe mutations in exons 4 and 5 of EFNB1. Of particular interest are the frameshift mutations located in the last 25 codons of EFNB1 encoding the carboxyterminal end of ephrin-B1. They result in an extension by 44 residues. These mutations disrupt the intracellular binding sites for Grb4 and PDZ-effector proteins involved in reverse signaling. We conclude that the major causes of familial as well as sporadic CFNS are loss of function mutations in the EFNB1 gene that comprise premature termination or abrogate receptor-ligand interaction, oligomerization, and ephrin-B1 reverse signaling.     

Mutation pattern in the Bruton's tyrosine kinase gene in 26 unrelated patients with X-linked agammaglobulinemia

Mutation pattern was characterized in the Bruton's tyrosine kinase gene (BTK) in 26 patients with X-linked agammaglobulinemia, the first described immunoglobulin deficiency, and was related to BTK expression. A total of 24 different mutations were identified. Most BTK mutations were found to result in premature termination of the translation product. Mutations were detected in most BTK exons with a predominance of frameshift and nonsense mutations in the 5′ end of the gene and missense mutations in its 3′ part, corresponding to the catalytic domain of the enzyme. Nonsense and frameshift mutations were associated with diminished levels of BTK mRNA expression, except for a frameshift mutation in exon 17 and two nonsense mutations in exon 2, indicating that these cases are not confined to penultimate exons. One amino acid substitution (R28H) was found in the pleckstrin homology domain's residue, which is mutated in mice bearing the X-linked immunodeficiency phenotype; another substitution (R307G) was identified in the src homology domain 2. All remaining amino acid substitutions were found in the catalytic domain of Btk. Hum Mutat 9:418–425, 1997. © 1997 Wiley-Liss, Inc.     

A novel SRY missense mutation affecting nuclear import in a 46,XY female patient with bilateral gonadoblastoma

Patients with disorders of sex development (DSD), especially those with gonadal dysgenesis and hypovirilization, are at risk of developing the so-called type II germ cell tumors (GCTs). Both carcinoma in situ and gonadoblastoma (GB) can be the precursor lesion, resulting in a seminomatous or non-seminomatous invasive cancer. SRY mutations residing in the HMG domain are found in 10–15% of 46,XY gonadal dysgenesis cases. This domain contains two nuclear localization signals (NLSs). In this study, we report a unique case of a phenotypical normal woman, diagnosed as a patient with 46,XY gonadal dysgenesis, with an NLS missense mutation, on the basis of the histological diagnosis of a unilateral GB. The normal role of SRY in gonadal development is the upregulation of SOX9 expression. The premalignant lesion of the initially removed gonad was positive for OCT3/4, TSPY and stem cell factor in germ cells, and for FOXL2 in the stromal component (ie, granulosa cells), but not for SOX9. On the basis of these findings, prophylactical gonadectomy of the other gonad was performed, also showing a GB lesion positive for both FOXL2 (ovary) and SOX9 (testis). The identified W70L mutation in the SRY gene resulted in a 50% reduction in the nuclear accumulation of the mutant protein compared with wild type. This likely explains the diminished SOX9 expression, and therefore the lack of proper Sertoli cell differentiation during development. This case shows the value of the proper diagnosis of human GCTs in identification of patients with DSD, which allows subsequent early diagnosis and prevention of the development of an invasive cancer, likely to be treated by chemotherapy at young age.     

Atypical breakpoint in a t(6;17) translocation case of acampomelic campomelic dysplasia

Campomelic dysplasia (CD) is a skeletal dysplasia characterized by Pierre Robin sequence (PRS), shortened and bowed long bones, airway instability, and the potential for sex reversal. A subtype of CD, acampomelic CD (ACD), is seen in approximately 10% of cases and preserves long bone straightness. Both syndromes are caused by alterations in SOX9, with translocations and missense mutations being overrepresented in ACD cases. We report a term infant with PRS, severe cervical spine abnormalities, eleven rib pairs, hypoplastic scapulae, and female genitalia. Chromosome analysis identified a 46,XY,t(6;17)(q25;q24) karyotype. FISH analysis with a series of BAC probes localized the translocation breakpoints to 6q27 and a region at 17q24.3 in the range of 459–379 kb upstream of SOX9. Therefore, this case extends the region classified as the proximal breakpoint cluster. In addition, the comorbidity of acampomelia, complete sex reversal, and severe spinal anomalies in our patient underscores the variability in the level of malformation in the CD/ACD family of disorders.     

Mutational and structural analysis of Japanese patients with mucopolysaccharidosis type II

We investigated mutations of the iduronate-2-sulfatase (I2S) gene and structural characteristics of I2S to clarify genotype/phenotype relationships in 18 Japanese patients with mucopolysaccharidosis type II. The I2S gene was analyzed in five patients with a severe phenotype and in 13 patients with an attenuated phenotype. The tertiary structural model of the human I2S was constructed by homology modeling using the arylsulfatase structure as a template. We identified four missense mutations and a nonsense mutation in the severe phenotype; four missense, two nonsense, three frame shifts, and one each of splice and amino acid deletion in the attenuated phenotype. Seven of them (L73del, Q75X, G140R, C171R, V401 fs, C422 fs, and H441 fs) were novel mutations. Structural analysis indicated that the residues of the mutations found in the severe phenotype would have direct interactions with the active site residues or should break the hydrophobic core domain of I2S, whereas residues of the missense mutations found in the attenuated phenotype were located in the peripheral region. In addition, effects by deletion or frameshift mutations could also be interpreted by the structure. Structural analysis of mutant proteins would help in understanding the genotype/phenotype relationships of Hunter disease.