Wolfanga L. Boson

PTCH Gene Mutations in Odontogenic Keratocysts

An odontogenic keratocyst (OKC) is a benign cystic lesion of the jaws that occurs sporadically or in association with nevoid basal cell carcinoma syndrome (NBCCS). Recently, the gene for NBCCS was cloned and shown to be the human homologue of the Drosophila segment polarity gene Patched (PTCH), a tumor suppressor gene. The PTCH gene encodes a transmembrane protein that acts in opposition to the Hedgehog signaling protein, controlling cell fates, patterning, and growth in numerous tissues, including tooth. We investigated three cases of sporadic odontogenic keratocysts and three other cases associated with NBCCS, looking for mutations of the PTCH gene. Non-radioactive single-strand conformational polymorphism and direct sequencing of PCR products revealed a deletion of 5 base pairs (bp) in exon 3 (518delAAGCG) in one sporadic cyst as well as mutations in two cysts associated with NBCCS, a nonsense (C2760A) and a missense (G3499A) alteration. This report is the first to describe a somatic mutation of PTCH in sporadic odontogenic keratocysts as well as two novel mutations in cysts associated with NBCCS, indicating a similar pathogenesis in a subset of sporadic keratocysts.

Thiopurine methyltransferase polymorphisms in a Brazilian population

ABSTRACTThiopurine methyltransferase (TPMT) catalyses the S-methylation of thiopurine drugs. Low-activity phenotypes are correlated with several mutations in the TPMT gene. Polymorphisms of TPMT have been reported for Caucasians, African-Americans and Asians. Since ethnic differences have been demonstrated worldwide, it remains to be elucidated in Brazil. The Brazilian population is the result of five centuries of interethnic crosses between peoples from almost all continents as well as autochthonous Amerindians, all forming the fifth largest and one of the most heterogeneous populations in the world. The frequency of six allelic variants of the TPMT gene, *2 (G238C) (2.2%), *3A (G460A and A719G) (1.5%), *3B (G460A) (0.2%), *3C (A719G) (1.0%), *5 (0%) and *6 (0%) were determined in Brazilian subjects using polymerase chain reaction (PCR)-RFLP and allele-specific PCR-based assays. This study provides the first analysis of TPMT mutant allele frequency in a sample of the Brazilian population.

A Novel Mutation of the Cathepsin C Gene in Papillon-Lefévre Syndrome

BACKGROUND Papillon-Lefévre syndrome (PLS) is a disorder that involves destruction of the periodontium and abnormal hyperkeratosis of the palms of the hands and soles of the feet. Mutations of the lysosomal protease cathepsin C gene (CTSC) have been associated with PLS. However, genotypic and phenotypic correlation has not been established. In the present study we investigated the CTSC gene in a Brazilian cohort affected by PLS. METHODS Eight consanguineous members of a kindred with PLS were studied. DNA was extracted and all exons of the gene amplified by the polymerase chain reaction (PCR) using specific primers. Mutations were identified by DNA sequencing of the coding region and introns of the CTSC gene. RESULTS Sequence analysis of CTSC from subjects affected by PLS identified a novel mutation (587T → C) in exon 4, predicted to cause a Leu196Pro amino acid substitution. Three of 3 subjects were homozygous for cathepsin C mutations inherited from a common ancestor. One patient was heterozygous and showed plantar hyperkeratosis without periodontal disease. Two other family members were also heterozygous but did not present palmoplantar hyperkeratosis and/or periodontal disease. CONCLUSIONS This study describes a novel mutation of the cathepsin C gene in a Brazilian kindred with Papillon-Lefévre syndrome. J Periodontol 2002;73:307-312.

Sporadic cardiac myxomas and tumors from patients with Carney complex are not associated with activating mutations of the Gsα gene

Abstract Cardiac myxomas are rare tumors that may be encountered sporadically or in the context of the Carney complex. The molecular basis for the development of cardiac myxomas and Carney complex tumors is unclear. Pathological myocardial function and myocardial hypertrophy have been associated with alterations in the heterotrimeric GTP-binding proteins. The postulated proto-oncogenic character of the gene encoding the alpha subunit of the stimulatory GTP-binding protein Gsα (gsp) in pituitary and thyroid tumors, the finding of identical somatic gsp mutations in the myocardium of patients with McCune-Albright syndrome, and the associated endocrine anomalies of the Carney complex prompted us to investigate the occurrence of activating missense mutations in the Gsα gene in 10 sporadically occurring atrial myxomas and in 8 tumors from 7 patients with Carney complex. No gsp mutations could be demonstrated by using the polymerase chain reaction and denaturing gradient gel electrophoresis complemented by direct DNA sequencing. Thus, activating Gsα mutations neither are associated with the development of atrial myxomas, nor can be demonstrated in other tumors from patients with Carney complex. The significance of these mutations in the myocardium of asymptomatic patients with McCune-Albright syndrome remains to be determined.

Novel mutations of the BSCL2 and AGPAT2 genes in 10 families with Berardinelli–Seip congenital generalized lipodystrophy syndrome

Context  Congenital generalized lipodystrophy, or Berardinelli–Seip syndrome, is a rare autosomal recessive disease caused by mutations in either the BSCL2 or AGPAT2 genes. This syndrome is characterized by an almost complete loss of adipose tissue usually diagnosed at birth or early infancy resulting in apparent muscle hypertrophy. Common clinical features are acanthosis nigricans, hepatomegaly with or without splenomegaly and high stature. Acromegaloid features, cardiomyopathy and mental retardation can also be present.

Investigation of A218C tryptophan hydroxylase polymorphism: association with familial suicide behavior and proband's suicide attempt characteristics

According to WHO, suicide accounts for about 1 000 000 deaths worldwide every year. In view of these dramatic data, several studies have tried to identify possible biological mechanisms and markers of suicide. Genes encoding for proteins involved in the serotonergic transmission are major candidates in association studies of suicidal behavior. The gene that codes for tryptophan hydroxylase (TPH), the rate‐limiting enzyme in the biosynthesis of serotonin, is one of these candidates. Two polymorphisms in intron 7 of this gene (A218C and A779C) have been described, but their role in suicidal behavior remains uncertain. TPH A218C polymorphism was analyzed in a sample of 248 psychiatric patients and 63 healthy controls. In addition, at least one close relative member was interviewed to assess family suicidal behavior history. Our research confirmed that a positive history of suicide attempts in a family member is associated with the chance of an individual to attempt suicide. Furthermore, we demonstrated that familial suicide attempts are more lethal and frequently more violent. We were not able to find significant differences of the TPH genotype frequencies between patients and controls. The TPH A218C genotypes were not associated with a history of suicide attempt and the lethality of the most lethal lifetime suicide attempt and suicide attempt method. The authors conclude that the A218C polymorphism of the TPH gene may not be a susceptibility factor for suicidal behavior in this group of psychiatric patients but confirm that a family suicidal behavior history increases the probands suicide attempt risk.

Clonal composition of human adamantinomatous craniopharyngiomas and somatic mutation analyses of the patched (PTCH), Gsα and Gi2α genes

Craniopharyngioma is the most common childhood tumor and thought to arise from embryonic remnants of Rathkes pouch. The paucity of published data on the molecular basis of these tumors prompted us to examine 22 adamantinomatous craniopharyngiomas looking for genetic abnormalities. Using the X-linked polymorphic androgen receptor gene as a tool for X-chromosome inactivating analysis, we found that a subset of craniopharyngiomas are monoclonal and therefore are probably due to acquired somatic genetic defects. Thus, we investigated these tumours for mutations within three candidate genes, Gsα, Gi2α and patched (PTCH). Using single stranded conformational polymorphism (SSCP), denaturing gradient gel electrophoresis and direct sequencing, the presence of somatic mutations in these genes could not be demonstrated in any tumor. Our data indicate that a subset of craniopharyngiomas are monoclonal and the mutations in the PTCH, Gsα, and Gi2α contribute little if any to cranipharyngioma development.

A signal peptide mutation of the arginine vasopressin gene in monozygotic twins

Familial neurohypophysial diabetes insipidus (FNDI) is a rare autosomal dominant syndrome stemming from the absence of arginine vasopressin (AVP). More than thirty‐five different germline mutations in the arginine vasopressin‐neurophysin II gene have been reported. These mutations are either in the signal peptide or scattered throughout the neurophysin II domain. A missense mutation altering alanine at position −1 to either valine or threonine in the signal peptide domain has previously been found in ten unrelated families. In the present report, Brazilian female monozygotic twins with clinically typical central DI in whom biochemical and molecular characterization were carried out are described. Direct mutational analysis by sequencing of the vasopressin gene in germline DNA revealed a heterozygous missense mutation (G→A) at nucleotide 279, predicting the substitution of alanine by threonine at position −1 of the signal peptide moiety. In summary, we present an extremely rare case of familial central diabetes insipidus in monozygotic Brazilian twins with a seemingly common missense mutation in the AVP gene.

Molecular analyses of the vasopressin type 2 receptor and aquaporin‐2 genes in Brazilian kindreds with nephrogenic diabetes insipidus

Nephrogenic diabetes insipidus (NDI) is associated with germline mutations in two genes: vasopressin receptor type 2 (V2(R)) in X‐linked NDI, and the water channel aquaporin‐2, in autosomal‐recessive disease. Genetic heterogeneity is further emphasized by reports of phenotypically abnormal individuals with normal structural genes. We analyzed both genes in five Brazilian families and the aquaporin‐2 gene in two Swedish families with clinical and laboratory diagnosis of NDI, by a combination of denaturing gradient gel electrophoresis (DGGE) and direct DNA sequencing. A novel polymorphism in the aquaporin‐2 gene (S167S), but no disease‐associated mutations in any tested individual from all seven families, was detected. In two Brazilian families, frameshift mutations were detected in the V2(R) gene: one leading to a premature stop after codon 36 and the other to a longer peptide (462 aa instead of the 373 aa wild‐type protein). In two other Brazilian families, probable disease‐associated missense mutations were detected: an alanine to proline at codon 163 (A163P) and an asparagine to aspartic acid at codon 85 (D85N). In one Brazilian family, both genes were structurally normal and the aquaporin‐2 gene was also normal in the two Swedish kindreds. This report further extends the mutational spectrum of NDI and suggests that there are other mutational or epigenetic events inactivating the two known genes or even novel genes that underlie NDI. Hum Mutat 14:233–239, 1999.

Nephrogenic Diabetes Insipidus (NDI): Clinical, Laboratory and Genetic Characterization of Five Brazilian Patients

INTRODUCTION: Nephrogenic diabetes insipidus is characterized by a lack of response in the distal nephron to the antidiuretic hormone arginine vasopressin. Manifestations include polyuria, polydipsia, hyposthenuria, recurrent episodes of dehydration and fever and growth failure. Most cases are caused by mutations in the AVPR2 gene. The mutant receptors are trapped intracellularly. METHOD: We studied five boys using clinical, laboratory and molecular data. The mean age at diagnosis was 14.6 months (range 6 to 24) and 12.2 years (7.8 to 19) after the follow-up period. The mean period of follow-up was 132.2 ± 50.9 months. RESULTS: The geometric means of the z-scores of weight and stature were −4.5 and −3.6, respectively, at diagnosis. At the last medical appointment, the z-scores of weight and stature were −0.3 and −0.9, respectively. Three patients were diagnosed with ureterohydronephrosis and exhibited increased post-void urine volume. Mutations in the AVPR2 gene were found in all patients, and the carrier status was confirmed in four of five cases. Two unrelated children presented identical mutations (S167L) in arginine vasopressin R2. Two of the patients had a mutation that has already been described in other Brazilian families (R337X), and one patient showed a de novo mutation (Y128D) in arginine vasopressin R2, since his mother’s molecular analysis was normal. The recurrence risk for this family was significantly reduced. CONCLUSION: This study reports the clinical and laboratory characterization of Nephrogenic diabetes insipidus and reiterates the importance of the genetic basis that underlies the disease diagnosis and genetic counseling.