|
|
||||||||
CLINICAL STUDY |
;an1
;i
nik21 Institute of Biochemistry, Faculty of Medicine, University of Ljubljana, Ljubljana, Slovenia, 2 University Childrens Hospital, Department of Pediatric Endocrinology, Diabetes and Metabolic Diseases, Vrazov trg 1 SI-1000, Ljubljana, Slovenia, 3 2nd Department of Paediatrics, Semmelweis University, Budapest, Hungary, 4 Department of Paediatrics, University of Szeged, Szeged, Hungary, 5 Department of Paediatrics, 3rd Faculty of Medicine, Charles University, Prague, Czech Republic, 6 Department of Paediatrics, Comenius University, Bratislava, Slovakia, 7 Department of Internal Medicine III, Division of Endocrinology and Metabolism, Medical University, Vienna, Austria and 8 Department of Paediatrics, Medical University, Vienna, Austria
(Correspondence should be addressed to T Battelino; Email: tadej.battelino{at}mf.uni-lj.si)
| Abstract |
|---|
|
|
|---|
Design and methods: Molecular analysis of the CYP21 gene was performed in 432 CAH patients and 298 family members. Low-resolution genotyping was performed to detect the eight most common point mutations. High-resolution genotyping, including Southern blotting and sequencing was performed to detect CYP21 gene deletions, conversions, point mutations or other sequence changes.
Results: CYP21 gene deletion and In2 and Ile172Asn mutation accounted for 72.7% of the affected alleles in the whole study group. A good genotypephenotype correlation was observed, with the exception of Ile172Asn and Pro30Leu mutations. In 37% of patients low resolution genotyping could not identify the causative mutation or distinguish homozygosity from hemizygosity. Using high-resolution genotyping, the causative mutations could be identified in 341 out of 348 analyzed patients. A novel mutation Gln315Stop was found in one simple virilising CAH (SV-CAH) patient from Austria. In the remaining seven patients polymorphisms were identified as the leading sequence alteration. The presence of elevated basal and ACTH-stimulated 17-hydroxyprogesterone, premature pubarche, advanced bone age and clitoral hypertrophy directly implicated Asn493Ser polymorphism in the manifestation of nonclassical- (NC) and even SV-CAH.
Conclusions: By genotyping for the most common point mutations, CYP21 gene deletion/conversion and the 8 bp deletion in exon 3, it should be possible to identify the mutation in 9499% of the diseased alleles in any investigated Middle European population. In patients with a mild form of the disease and no detectable mutation CYP21 gene polymorphisms should be considered as a plausible disease-causing mutation.
| Introduction |
|---|
|
|
|---|
The Middle European Society for Pediatric Endocrinology (MESPE) has created a large database since 1998 containing information on 598 children with CAH from Austria, the Czech Republic, Hungary, Slovakia and Slovenia in order to study the endocrinological parameters, the efficiency of clinical diagnostics and the treatment and genetics of CAH in Middle European countries (1113). The database is described in detail elsewhere (11).
The aim of this study was to systematically analyze the mutational spectrum and the genotypephenotype correlation in CAH patients and their family members registered in the MESPE-CAH database. Furthermore, we aimed to design a rational approach for CYP21 mutation detection needed for reliable pre-, peri- and postnatal diagnostics and for genetic counseling in the Middle European countries and in ethnic groups originating from the region.
| Subjects and methods |
|---|
|
|
|---|
Patients from the MESPE-CAH database and their family members were invited to participate in the study and written informed consent was obtained from all the participants. The respective national ethics committees for research in medicine approved the study design. The clinical and laboratory data on the patients were available on the database. The clinical diagnosis of different types of 21-OH deficiency was made by paediatric endocrinologists based on the history, physical examination, electrolyte and hormonal data (1, 14). Patients were considered to have the SW form when clinical and laboratory signs of renal salt wasting were present in the first month of life; the SV form was assigned if clinical symptoms of CAH without SW were present before the age of puberty onset, i.e. 8 years, and the NC form when symptoms of androgen excess became evident during or after puberty (11). Patients without reliable clinical information were excluded from the study.
Methods
National coordinators were asked to provide peripheral blood or genomic DNA samples of patients and their first-degree relatives for genotyping. Out of 598 CAH patients from the five Middle European countries included in the MESPE-CAH database peripheral blood or genomic DNA samples were available from 476 patients (79.6%). Sequence analysis was used to detect CYP21 gene mutations in Austrian patients using the approach previously described (15). For patients from other countries a two-step genotyping approach was employed. Low-resolution genotyping for 8 common point mutations was performed using allele-specific polymerase chain reaction (PCR-SSP) and/or PCR and sequence specific oligonucleotide hybridisation (PCR-SSO) by participating centers (1618). High resolution genotyping by PCR-SSP, PCR-SSO, Southern blotting and sequencing was performed in Ljubljana to detect CYP21 gene deletions, conversions, point mutations or other sequence changes when mutation could not be identified on one or both alleles by low resolution genotyping or when homozygosity could not be distinguished from hemizygosity. The genotyping approach is described in detail elsewhere (17, 18). The reference sequence reported by White et al. (4) was used for numbering of nucleotides and amino acids.
| Results |
|---|
|
|
|---|
Using low-resolution genotyping mutations could not be identified or homozygosity could not be distinguished from hemizygosity in 160 out of 432 patients (37%). From 84 of these patients DNA was not available for further analysis. Using high-resolution genotyping, Southern blotting and sequencing the causative mutations could be identified in 341 out of 348 (98.0%) patients while in the remaining seven patients polymorphisms were identified as the leading sequence alteration.
A novel mutation Gln315Stop (Fig. 1
) resulting in a premature stop codon which has not been described to date in CAH patients, was found in a patient from Austria. The girl was diagnosed at age 4·4 and was clinically SV. The sequencing analysis of both parents confirmed the inheritance of a Gln315Stop mutation from her mother and of a Pro30Leu mutation from her father.
|
|
|
|
In seven patients polymorphisms were identified to be the leading sequence alteration as the direct sequencing of all exons, introns and the proximal promoter region of CYP21 gene did not reveal any putative new mutation. Among these patients three were homo- or hemizygous for Asn493Ser and three were compound heterozygotes for this substitution. The clinical characteristics of these patients are given in Table 4
. Most of the patients with Asn493Ser presented with elevated baseline or ACTH-stimulated 17OHP levels, premature pubarche or advanced bone age and one girl had clitoral hypertrophy. Elevated basal 17OHP levels were also observed in the NC patient hemizygous for the Lys102Arg Ser268Thr polymorphism, who also presented with clitoral hypertrophy.
|
| Discussion |
|---|
|
|
|---|
We found a Gln315Stop substitution in one SV-CAH patient from Austria. This mutation has not been described to date in CAH patients and results in a premature stop codon. Although a functional assay has to be performed to determine the residual enzyme activity of this mutation in vitro we assume that such a mutation would completely abolish enzyme activity, similarly to the nearby Gln318Stop mutation. This would also explain a SV phenotype in this patient carrying Pro30Leu mutation on the less affected haplotype.
The large number of patients included in this study enabled us to analyze the genotypephenotype correlation. In general a good genotypephenotype correlation was observed in patients with severe mutations, however carriers of the Ile172Asn and Pro30Leu mutations on the less affected allele displayed a greater variability of clinical phenotypes. This phenotypic variability of Ile172Asn mutation has also been reported in other European populations showing an otherwise good correlation between the genotype and phenotype (3, 10, 19, 20). Similarly, many investigators have reported phenotypes more severe than expected in carriers of the Pro30Leu mutation (9, 10, 15, 18, 21). The finding of the Pro30Leu mutation linked to a gene conversion in the promoter region or with an additional mutation, Ala15Thr, could explain the increased severity of phenotypes in Slovenian patients (18). The in vitro expression analysis did not demonstrate the impairment of enzyme activity by Ala15Thr mutation alone (22) but it is not excluded that this mutation has a synergistic effect on 21-hydroxylase activity when combined with the Pro30Leu mutation and/or gene conversion in the promoter region (23).
The relatively slight differences in the distribution of CYP21 mutations observed between individual countries within the Middle European region suggest that, despite differences in ethnic origins, similar genetic mechanisms were probably involved in the transmission of the disease. A possible explanation for this may be a high degree of ethnic mixing over the centuries in some populations (16). The observed frequencies of the CYP21 gene deletion (range 13.937.2%) and In2 mutation (range 16.750.0%) were comparable to the frequencies observed in most of the other European countries. In CAH patients from the Middle European populations studied, the frequencies of the Val281Leu mutation (range 1.55.6%) were lower than in Italy, France and Spain (range 11.016.7%), but comparable to other European countries (range 2.25.7%). The frequencies of Pro30Leu in Middle European populations (range 2.19.2%) were higher, particularly in Austrian CAH patients than in other European populations (range 0.32.7%) (8, 10, 20, 2426).
A high frequency of alleles with multiple mutations was found: 5.6% of the alleles in the whole study group and 15.4% of all the alleles in Slovenian patients carried two or more mutations. The clustering of point mutations on one allele has been previously reported in 1.9% of unrelated alleles in Dutch patients (20). The relatively high frequency of alleles with multiple mutations in Middle European patients compared to some other single point mutations considered to be common in CAH, such as Gln318Stop (2.6%) and Arg356Trp (2.4%), demonstrates the importance of including the parents of the index case in the molecular analysis if segregation of alleles needs further determination. If families are not available, mutations can be allocated to separate alleles by allelespecific PCR amplifications (8).
By low-resolution genotyping for the eight most common CYP21 point mutations, mutations could not be identified or homozygosity could not be distinguished from hemizygosity in 37% of patients. Using high-resolution genotyping, PCR-SSP amplification and Southern blotting for the detection of CYP21 gene deletion and large gene conversions only 2% of alleles remained unidentified. Among these, direct sequencing of CYP21 identified Asn493Ser substitution as the leading sequence change in six patients. Some authors describe this substitution as a naturally occurring polymorphism (27) and some as a disease causing mutation (28) but its influence on residual enzyme activity has never been analyzed in vitro. In Mexican CAH patients a higher proportion of homozygosity for the Asn493Ser substitution was observed than in a healthy population (29). It was proposed that a synergistic effect between two mutations could lead to decreased enzymatic activity in CAH patients homozygous for Ser268Thr and Asn493Ser (30, 31), but, except in one patient with a T-107C substitution and one patient with concomitant Lys102Arg on one haplotype, the sequencing of all the exons, introns and 340 nucleotides of the proximal promoter region revealed no other sequence alteration on alleles characterised by Asn493Ser. The presence of elevated basal and ACTH-stimulated 17OHP, premature pubarche, advanced bone age in all patients and also clitoral hypertrophy in one girl implicates a direct role of this substitution in the disease manifestation of NC and even SV-CAH.
Lys102Arg and Ser268Thr mutations were also reported to be normal polymorphisms, however, a synergistic effect resulting in a decreased enzymatic activity was observed when both mutations were transmitted on the same haplotype (30, 31). This could explain the finding of clitoral hypertrophy and elevated basal 17OHP levels in one NC patient hemizygous for Lys102Arg Ser268Thr substitutions.
In conclusion, our genotyping approach allowed accurate and sensitive identification of CYP21 gene mutations in CAH patients and their families and offered reliable information needed for diagnostics and for adequate genetic counselling in the Middle European countries and in ethnic groups originating from the region. A novel Gln315Stop mutation was identified. By genotyping for the most common point mutations, CYP21 gene deletion/conversion and the 8 bp deletion in exon 3, it should be possible to identify the responsible mutation in 9499% of the diseased alleles in any investigated population. In patients with a mild form of the disease and a normal genotype at all positions, CYP21 gene polymorphisms such as Asn493Ser should be considered as a plausible disease causing mutation.
| Acknowledgements |
|---|
ková, J Lebl, L Lisá, V Procházková, S Prùhová, R Prùsa, J Skvor, M
najderová, J Venhácová, F Votava, J Zapletalová and J Zeman; Hungary: É Erhardt, Z Halász, I Ilyés, J Kovács, K Láng, E Nagy, T Niederland, F Péter, L Ságodi, G Soltész, E Só lyom, J Sólyom, L Szabó and P Szüts; Slovakia: S Bielikova, M Debreova, J Javorkova, L Kostalova, M Kusekova, Z Misikova, Z Priblincova, J Strnova, Z Simekova and D Trezova; Slovenia: T Battelino, N Bratani
, V Dol
an, C Kr
i
nik, Mojca Zerjav-Tansek, B Repi
-Lampret, M Stopar-Obreza, and K Trebu
ak.
| References |
|---|
|
|
|---|
an V, Pre
elj J, Vidan-Jeras B & Breskvar K. Adrenal 21- hydroxylase gene mutations in Slovenian hyperandrogenic women: evaluation of corticotrophin stimulation and HLA polymorphisms in screening for carrier status. European Journal of Endocrinology 1999 141 132139.[Abstract]
18. Dol
an V, Stopar-Obreza M,
erjav-Tan
ek M, Breskvar K, Kr
i
nik C & Battelino T. Mutational spectrum of congenital adrenal hyperplasia in Slovenian patients: a novel Ala15Thr mutation and Pro30Leu within a larger gene conversion associated with a severe form of the disease. European Journal of Endocrinology 2003 149 137144.[Abstract]
19. Jaaskelainen J, Levo A, Voutilainen R & Partanen J. Population-wide evaluation of disease manifestation in relation to molecular genotype in steroid 21-hydroxylase (CYP21) deficiency: good correlation in a well defined population. Journal of Clinical Endocrinology and Metabolism 1997 82 32933297.This article has been cited by other articles:
![]() |
M. Bidet, C. Bellanne-Chantelot, M.-B. Galand-Portier, V. Tardy, L. Billaud, K. Laborde, C. Coussieu, Y. Morel, C. Vaury, J.-L. Golmard, et al. Clinical and Molecular Characterization of a Cohort of 161 Unrelated Women with Nonclassical Congenital Adrenal Hyperplasia Due to 21-Hydroxylase Deficiency and 330 Family Members J. Clin. Endocrinol. Metab., May 1, 2009; 94(5): 1570 - 1578. [Abstract] [Full Text] [PDF] |
||||
![]() |
L. G. Gomes, N. Huang, V. Agrawal, B. B. Mendonca, T. A. S. S. Bachega, and W. L. Miller Extraadrenal 21-Hydroxylation by CYP2C19 and CYP3A4: Effect on 21-Hydroxylase Deficiency J. Clin. Endocrinol. Metab., January 1, 2009; 94(1): 89 - 95. [Abstract] [Full Text] [PDF] |
||||
![]() |
C. Moran, R. Azziz, N. Weintrob, S. F. Witchel, V. Rohmer, D. Dewailly, J. A. M. Marcondes, M. Pugeat, P. W. Speiser, D. Pignatelli, et al. Reproductive Outcome of Women with 21-Hydroxylase-Deficient Nonclassic Adrenal Hyperplasia J. Clin. Endocrinol. Metab., September 1, 2006; 91(9): 3451 - 3456. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |