De novo mutation in the BTK gene of atypical X-linked agammaglobulinemia in a patient with recurrent pyoderma.

BACKGROUND: X-linked agammaglobulinemia (XLA), characterized by a profound deficiency of all immunoglobulins and the absence of mature B cells, is caused by mutations in the gene encoding Bruton tyrosine kinase (BTK). Most patients have recurrent sinopulmonary infection. Infections usually occur in multiple locations across time, but single infection may be limited to one anatomic location. OBJECTIVES: To report a case of atypical XLA with recurrent pyoderma and to observe the immunologic changes in the patient in 10 years. METHODS: Immunologic investigations, skin wound culture, and molecular study with DNA sequencing were performed. RESULTS: The patient was originally diagnosed as having common variable immunodeficiency disease because of the presence of circulating B cells (CD19+ B cells: 7%) at 11 years old. On further evaluation at the age of 20 years, flow cytometric analysis of lymphocytes showed only 0.4% B cells. The molecular study with DNA sequencing of the patient showed a point mutation in complementary DNA 1630 A>G(p.R544G) in the BTK gene, indicating that the patient has XLA. The mutation analysis of the BTK gene revealed a normal DNA sequence in the other family members. CONCLUSIONS: This case is an important example of a possible presentation of XLA with a predominant skin manifestation, and it demonstrates that maintaining a high level of clinical suspicion is essential for the diagnosis of XLA in a child with recurrent pyoderma.     

Novel missense mutation (R94S) in the TAZ ( G4.5) gene in a Japanese patient with Barth syndrome

Barth syndrome (BTHS) is a rare X-linked disorder characterized by cardiomyopathy, short stature, neutropenia, and 3-methylglutaconic aciduria. Mutations have been identified in the TAZ (G4.5) gene in patients with BTHS. This article presents a mutation analysis of this gene in a Japanese boy with cardiomyopathy with abnormal mitochondria, cyclic neutropenia, and 3-methylglutaconic aciduria (type 2). The analysis revealed a novel missense mutation (R94S) caused by a single nucleotide substitution (C-to-A) in this patient. Received: November 30, 2001 / Accepted: February 9, 2002     

Novel missense mutation (Leu466Arg) of the DAX1 gene in a patient with X-linked congenital adrenal hypoplasia

We identified a DAX1 missense mutation, a substitution of arginine for leucine at codon 466 (Leu466Arg), in an infant with X-linked congenital adrenal hypoplasia (AHC). A heterozygous substitution, Leu466Arg, was also identified in his mother and sister. Since leucine at position 466 is well conserved among other orphan nuclear hormone receptor superfamilies and Leu466Arg was not detected among 50 normal Japanese control individuals, the mutation is most likely responsible for X-linked AHC. It is interesting to note that Leu466Arg among all mutations ever reported is located at the most C-terminal region of the DAX-1 protein. Most mutations identified previously were located in the C-terminal presumptive ligand binding domain. Hence, the C-terminal end of the DAX-1 protein may play an important role in the biological function, such as in normal adrenal embryogenesis. Am. J. Med. Genet. 84:87–89, 1999. © 1999 Wiley-Liss, Inc.     

Twin carriers of X-linked agammaglobulinemia (XLA) due to germline mutation in the Btk gene

We report on an X-linked agammaglobulinemia (XLA) family in which mothers of two affected cousins were monozygotic twins. We analyzed the Btk gene of several members in three generations of the family by SSCP analysis, DNA sequencing, and RFLP analysis following polymerase chain reaction-amplification of the individual exons. We identified a missense point mutation, G1817C (R562P), in exon 17 of the Btk gene in the affected cousins. The same mutation was also present in both mothers (twin sisters) of the cousins identifying them as carriers. However, the mutation was absent in all other relatives including the grandmother of the cousins (mother of the twin sisters). This strongly suggests that the mutation in the Btk gene had originated in one of the germ lines or in the zygote. This may be the first demonstration of a germ line (or zygotic) mutation in XLA.     

Autoimmune lymphoproliferative syndrome (ALPS) in a patient with a new germline Fas gene mutation

Autoimmune lymphoproliferative syndrome (ALPS) is a rare genetic disorder characterized by chronic lymphoproliferation, autoimmune manifestations and expansion of TCRalphabeta+CD4-CD8- lymphocytes. The main pathogenic factor is a defective Fas-mediated apoptosis generally caused by mutations in the Fas gene. This report describes a new heterozygous Fas gene mutation in a boy with clinical and immunological features of ALPS. In vitro, T-cell blasts from the patient are completely resistant to the effects on the anti-Fas cytotoxic mAb CH-11, they also have a higher proliferation rate than T cells from healthy donors, while PHA-induced AICD is normal. The location of the mutation (I246S) found in the intracytoplasmic death domain, and the conservation of that residue in four different species from human suggest that I246 is an essential amino acid for Fas function. The patient has inherited the mutation from his father who also shows defective Fas-mediated apoptosis but the clinical and immunological manifestations are much less severe. These results provide evidence that the penetrance of genetic defects in Fas is variable and that other factors may influence the phenotype of the disease.     

Novel missense mutation (Leu466Arg) of the DAX1 gene in a patient with X-linked congenital adrenal hypoplasia.

We identified a DAX1 missense mutation, a substitution of arginine for leucine at codon 466 (Leu466Arg), in an infant with X-linked congenital adrenal hypoplasia (AHC). A heterozygous substitution, Leu466Arg, was also identified in his mother and sister. Since leucine at position 466 is well conserved among other orphan nuclear hormone receptor superfamilies and Leu466Arg was not detected among 50 normal Japanese control individuals, the mutation is most likely responsible for X-linked AHC. It is interesting to note that Leu466Arg among all mutations ever reported is located at the most C-terminal region of the DAX-1 protein. Most mutations identified previously were located in the C-terminal presumptive ligand binding domain. Hence, the C-terminal end of the DAX-1 protein may play an important role in the biological function, such as in normal adrenal embryogenesis.     

Bruton tyrosine kinase gene mutations in Turkish patients with presumed X‐linked agammaglobulinemia

X‐linked agammglobulinemia (XLA) is a ptototypical humoral immunodeficiency caused by mutations in the gene coding for Bruton tyrosine kinase (BTK). The genetic defect in XLA impairs early B cell development resulting in marked reduction of mature B cells in the blood. Studies from different countries have demonstrated that approximately 90% of males with presumed XLA bear mutations in BTK. In this study, we report for the first time the occurrence of BTK mutations in Turkey. We performed mutational analysis of the BTK gene in 16 Turkish male patients from 13 separate families with presumed XLA based on abnormally low peripheral blood B‐cell numbers (lt; 1%), hypogammaglobulinemia, and recurrent bacterial infections. We found that in nine of the 13 families (69%) a Btk mutation caused XLA. Two of the mutations were previously described, but seven novel mutations were identified: two missense (Y39C, G584R), one nonsense (Q343X), and 4 deletions (1800‐1821del, 1843‐1847del, 1288‐1292del, 291del) resulting in frameshift and premature stop codon. By contrast, no mutations in the BTK gene were identified in the other 4 families. A consanguinity in three of these families raises the possibility that mutations in other autosomal genes which affect early B cell development may contribute to their phenotype resembling XLA. Hum Mutat 18:356, 2001. © 2001 Wiley‐Liss, Inc.     

Novel intronic germline FLCN gene mutation in a patient with multiple ipsilateral renal neoplasms

Multiple renal tumors of diverse morphology are rare and typically seen in Birt-Hogg-Dubé syndrome. Birt-Hogg-Dubé syndrome is a rare inherited cancer syndrome caused by a germline mutation in the folliculin (FLCN) gene, but the genetic causes for histologic diversity of renal tumors in Birt-Hogg-Dubé syndrome have not been elucidated. We describe here a 64-year-old man with a novel germline mutation in the FLCN gene who presented with 3 phenotypically distinct renal tumors in the same kidney, which were histologically classified as oncocytoma (1.4 cm), oncocytic papillary carcinoma (0.5 cm), and clear cell renal carcinoma (0.8 cm). Genetic analysis of normal kidney tissue revealed a heterozygous germline FLCN mutation (intron 9, IVS9+6 C>T). Additional molecular genetic testing revealed somatic mutations and epigenetic events in genes typically associated with these specific histologic tumor types: oncocytoma harbored a second FLCN mutation (intron 12, IVS12+4 C>T), oncocytic papillary carcinoma harbored promoter methylation of FLCN, and a missense mutation in the MET gene (P246L), whereas clear cell carcinoma harbored inactivating VHL mutation (5–base pair deletion in exon 2) and VHL gene promoter methylation. In addition, chromosomal analysis of peripheral blood lymphocytes showed low level chromosome instability, not previously associated with germline mutations in the FLCN gene.