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Institute of Molecular Pathology and Immunology of University of Porto (J.L., T.F., A.F.d.S., I.P.-C., V.M., M.S.-S., G.G.-R.) and Medical Faculty (J.L., M.S.-S.), University of Porto, 4200–465 Porto, Portugal; Institute of Molecular and Cellular Biology (IBMC) (G.F.-B.), Miguel Hernandez University, Elche, 03202 Alicante, Spain; Department of Pathology (A.H.), School of Medicine, Oviedo University, Oviedo, 33006 Asturias, Spain; Department Structural and Computational Biology (L.S.), European Molecular Biology Laboratory, Heidelberg, 69117 Germany and Systems Biology Programme, Centre for Genomic Regulation, 08003 Barcelona, Spain; and Hospital S. João (M.S.-S.), 4202–451 Porto, Portugal
Address all correspondence and requests for reprints to: Ginesa Garcia-Rostan, M.D., Ph.D., Dr. Alfredo Martinez, No. 3, 3°B, 33005 Oviedo-Asturias, Spain. E-mail: ginesarostan{at}telefonica.net.
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Abstract |
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Design: Thirty-six sporadic cervical PGLs and four familial PGLs were investigated by PCR-single-strand conformation polymorphism analysis and sequencing. Computational biology was applied to address the structural-conformational changes behind missense mutations and, simultaneously, infer the possible consequences in protein function.
Results: Eight sporadic cases (22.2%) carried pathogenic germline mutations, six of which were in SDHB and two in SDHD. Three families had mutations in SDHD and one in SDHB. Seven of 11 different pathogenic mutations (64%) affected SDHB. Ten mutations were novel. Missense mutations were primarily found in SDHB and frameshift mutations in SDHD. Missense SDHB mutations seemed to alter the enzymatic activity by hampering the electron transfer. SDH-linked tumors occurred mainly in males (P = 0.0033), occurred at a younger age (P < 0.0001), were usually multifocal (P = 0.0011), and exhibited a larger size (P = 0.0341).
Conclusions: A significant proportion of sporadic cervical PGLs arise as a consequence of intrinsic genetic factors. At variance with previous reports, SDHB is frequently mutated in sporadic cervical PGLs and the mutations do not entail a deleterious behavior. Therefore, SDHB genetic testing may be considered in all subjects presenting with solitary cervical PGL and no family history.
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Introduction |
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Familial PGL is a genetically heterogeneous disorder (OMIM 168000), which involves various chromosomal loci. In 1997, linkage analyses in several unrelated Dutch and North American PGL families revealed two loci, 11q23.1 and 11q13, that segregated with the disease (7). In 2000, Baysal et al. (8) showed that germline loss-of-function mutations in SDHD at 11q23.1 caused familial PGL. Shortly afterward, studies based on direct candidate gene analyses demonstrated that germline mutations in two other genes at chromosome 1, SDHB (1p36.13) and SDHC (1q23.3), were also involved in familial PGL (9, 10). The causative gene mapping at 11q13 still awaits identification.
SDHB, SDHC, and SDHD genes (SDH genes) are nuclear genes that code for the SDHB, SDHC, and SDHD subunits of the heterotetrameric mitochondrial enzyme succinate dehydrogenase (SDH). The SDHB subunit, also known as iron-sulfur protein, is part of the hydrophilic catalytic domain and is highly conserved throughout species. SDHB is directly bound to SDHA, which contains the flavin-adenine dinucleotide (FAD) prosthetic group and the substrate binding site, and to SDHC and SDHD, which together anchor SDH to the mitochondrial inner membrane and provide the ubiquinone binding site. SDHC and SDHD harbor the heme group to which the electrons are transferred from the iron-sulfur clusters: FES (2Fe-2S), FS4 (4Fe-4S), and F3S (3Fe-4S). These iron-sulfur clusters are located within SDHB and act as redox centers, transporting the electrons derived from the FAD prosthetic group (reduced on oxidation of succinate) to the membrane soluble transporter ubiquinone, which will then enter the oxidative phosphorylation (OXPHOS) system (11, 12).
So far, the majority of the studies dealing with germline SDH mutations in PGL patients have been carried out in North European and/or North American populations. These studies, besides revealing an evident familial clustering of the disease, with three founder mutations in The Netherlands, have also shown that a subset of apparently sporadic cervical PGLs harbor germline mutations in SDH genes. The latter individuals represent occult familial cases with incomplete/low penetrance of the mutated allele (13, 14).
Although germline mutations in SDHB and/or SDHD have been reported in apparently sporadic and familial cervical PGLs (70–90% of familial cervical PGLs and 
8% of sporadic cervical PGLs), the overall mutation frequency for each of these two genes is significantly different. Mutations in SDHD are considered the major cause of cervical PGLs. To date, 94 and 69 unique allelic variants have been described in SDHB and SDHD, respectively (http://chromium.liacs.nl/lovd_sdh) (15). The prevalence of SDHC mutation carriers among cervical PGL patients is much lower. Only nine different allelic variants, primarily associated with familial presentations, have been annotated in SDHC (16).
The accumulated data indicate that there is some variation in the prevalence, penetrance, and phenotypic expression of the SDH mutations among different populations. Understanding the cause/s of these variations is important for the genetic counseling and proper management of PGL patients. In this study, we sought to determine whether germline mutations in SDHB, SDHC, and/or SDHD play a role in the nosology of cervical PGLs from northern Spain, where this disorder is particularly frequent. We also assessed whether there is any difference with respect to the overall mutation prevalence, mutation pattern, and penetrance reported in other populations. Because some missense substitutions may result in partially functional mutant proteins that could account for the reduced/incomplete penetrance observed in some SDH mutation carriers, we also addressed the structural-functional consequences behind punctual, unreported SDHB mutations.
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Patients and Methods |
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Individuals diagnosed with cervical PGL at the Hospital Central de Asturias (Spain), between 1981 and 2005, were identified by retrospectively reviewing the clinicopathological records and direct patient/family interview. Forty unrelated cases (36 sporadic and four inherited) were enrolled in the study due to the availability of DNA from peripheral blood leukocytes, tumor tissue, and clinical data. All histological diagnoses were reviewed according to established morphological criteria (3, 4). Sporadic cases were defined as those having no familial history of PGLs in the parental and grandparental generations. Disease was considered to be inherited when at least two first-degree relatives, preferentially from different generations, or two second-degree relatives were affected by PGLs. Patients displaying syndromic features associated with von Hippel Lindau disease (VHL), multiple endocrine neoplasia type 2 (MEN2), or neurofibromatosis type 1 (NF1) were excluded from the study population. Only the index patient of each family entered in the first screening of mutations. Missense mutations were regarded as pathogenetically relevant if not found among 203 anonymous healthy blood donors residing in the same geographic area of the patients. Identification of a putative disease-causing mutation was followed by genetic testing of all at risk living relatives of the mutation carriers.
Informed consent for genetic testing was obtained from all patients, relatives, and control cases. Processing of samples and of patient information was in agreement with protocols approved by the corresponding ethical committees.
Mutational analysis
Genomic DNA was extracted from peripheral blood leukocytes using a standard salt-precipitation method (17). Matching tumoral DNA was extracted from formalin-fixed, paraffin-embedded specimens according to a previously described protocol (18). When necessary, tumors were microdissected to increase the proportion of neoplastic cells, which always represented at least 80% of the total.
The occurrence of SDHB, SDHC, and/or SDHD mutations was evaluated by PCR-single-strand conformation polymorphism analysis (SSCP). Primers and PCR/SSCP conditions are available on request. All mobility shifts observed in the SSCP analysis were ratified by repeating the PCR-SSCP assay.
Whenever a sample displayed recurrent aberrant SSCP conformers, the respective PCR product was purified using the GFX PCR DNA and gel band purification kit (Amersham Biosciences, Piscataway, NJ). The purified target DNA was subjected to automatic sequencing (ABI PRISM 3100 genetic analyzer; Applied Biosystems, Foster City, CA), using the BigDye terminator version 3.1 cycle sequencing kit (Applied Biosystems). Sense and antisense sequencing was performed for confirmation. All mutations were further verified by PCR and direct sequencing from a new DNA template.
Structural analysis of SDHB mutations
The structure of the human mitochondrial enzyme SDH was modeled at 2.4A resolution (1ZOY.PDB) by means of homology with the recently solved crystal structure from porcine heart (19). The porcine structure sorts out the low sequence homology found in the integral membrane anchors of the prokaryotic counterpart (20) and overrides the absence of the ubiquinone binding sites, providing a reliable model to study the structural-conformational changes induced by human mutations as well as their relationship with human mitochondrial pathologies. Modeling was performed upon sequence alignment using the BuildModel function implemented in Fold-X (21, 22). During this procedure Fold-X performs the mutagenesis while testing different rotamers, allowing neighbor side chains to move. The emerging models undergo additional optimization by the Repair function of Fold-X, where those residues that have bad torsion angles or van der Waals clashes are identified and corrected.
The structure was edited with Swiss-PDB viewer 3.7 (23) and all the molecular graphics created with Pymol (24). The comparison between wild-type and mutated models gives the opportunity to understand the structural consequences behind punctual mutations.
Statistical analysis
The Fisher’s exact test, ANOVA test, and 
2 test with the Yates correction were applied in the statistical computing (Statview; SAS Inc., Cary, NC). P 
0.05 was considered statistically significant.
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Results |
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Among the 48 patients diagnosed with PGL, 36 (75%) had no family history and 12 (25%) inherited the disease. The clinical and pathological features (Table 1
) closely paralleled those described in most larger series (3, 4). Apparently sporadic carotid body tumors was the only group in which a higher prevalence of males (five of eight, 63%) was detected. In the familial group, nearly 38% of the patients with carotid body PGLs showed bilateral, synchronous, or metachronous tumors. Tympanic PGLs were detected only in sporadic presentations (P = 0.0213), displayed a smaller size (average 0.8 cm), and occurred preferentially in females (nine of 10).
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The mean follow-up time was similar in both groups (7 yr). All the sporadic patients who developed a tumor recurrence had undergone resection of a single jugular (two of five) or jugulotympanic (three of five) PGL. Up to the last follow-up performed in this cohort, no patient had evidenced local and/or distant metastases. Only one familial patient bearing extra-adrenal PGLs died of the disease. It is noteworthy that 73% of the patients had lived near the sea level or at low altitudes.
Molecular genetics
Twenty-five of the 40 PGL patients (62.5%) initially enrolled in the germline mutational screening revealed aberrant SSCP conformers. The type of alteration, exonic/intronic location, altered nucleotide position, specific nucleotide change, and corresponding amino acid substitution are summarized in Table 2.
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Frameshift coding alterations were more likely to appear in SDHD (80%) and missense alterations in SDHB (62.5%). The ratio of different nonsynonymous to different synonymous sequence variants was 3:1 for SDHD and 5:3 for SDHB. Most of the missense sequence variants were transitions and involved residues highly conserved among species (87.5%, seven of eight). The only missense transversion (R17L in SDHD) observed in this cohort affected an amino acid conserved in mammals but not in bacteria. Six of nine SDHB (67%) (C93R, C186Y, P197S, P254L, L180L, and c.312InsCACTGCA), one SDHC (100%) (IVS1 + 13 InsTG), and three of seven SDHD (43%) (R17L, c.383–386InsT, and c.120–127DelCCCAGAAT) sequence alterations had not been previously reported (http://chromium.liacs.nl/lovd_sdh) (15). Sequence alterations in the SDHD gene were roughly equally distributed throughout all four exons, whereas those in the SDHB gene tended to cluster in exon 1 (50%) followed by exon 4 (19%) and were not seen in exons 2 and 8.
Four coding sequence variants were present in the chromosomes of healthy individuals: G12S (three of 186; 1.6%), H50R (three of 274; 1%), and S68S (9 of 252; 3.6%) for SDHD and A6A (two of 182; 1%) for SDHB. The two intronic sequence variants, IVS2–36G>T in SDHB and IVS1 + 13 InsTG in SDHC, detected in 15 PGL patients, were also found in 12.8% (52 of 406) and 6.3% (12 of 192) healthy control cases, respectively. All six alterations will be designated hereafter as polymorphisms.
After excluding the aforementioned polymorphisms, it emerged a trend for an association of pathogenic missense mutations with SDHB (five of six, 83%) and frameshift mutations with SDHD (four of five, 80%) (P = 0.0801).
Sporadic paragangliomas
Sixteen patients (44.4%) carried germline coding alterations [12 (75%) in SDHB, three (19%) in SDHD and one (6%) in both genes] (Table 2
). The only germline alteration observed in SDHC was an intronic polymorphism (IVS1 + 13 InsTG).
A total of 13 different germline coding alterations were identified, including seven nonsynonymous/missense alterations (54%), four synonymous alterations (31%), and two frameshift alterations (15%). All these germline alterations were confirmed at the somatic level and no additional somatic changes were observed. Figure 1 shows the SSCP patterns and sequencing chromatograms of representative SDHD and SDHB mutation carriers.
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). To further verify the splicing, a fragment encompassing part of exon 5 up to exon 7 was amplified and sequenced. The chromatogram showed the peak corresponding only to the wild-type allele (G) and not two superimposed peaks (G and A) as it would be expected if both alleles were correctly transcribed and spliced (Fig. 2B).
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Structural biology studies revealed that all the SDHB missense mutations are predicted to alter the enzymatic activity by disrupting the anchoring to the FES, FS4, and F3S clusters present within the catalytic core of SDH. Some also may affect the interaction with other subunits of mitochondrial SDH such as flavoprotein (SDHA). Of note, the P197S mutation could hamper the binding of the ubiquinone. The mutation is placed in a pocket surrounded by hydrophobic and aromatic residues. The polar group of serine could directly clash with the ubiquinone ring, could hydrogen bond to W201, or both, breaking the binding of the ubiquinone to chain B and thus avoiding electron transfer. In addition, the adoption of dihedrals slightly forced for serine could induce a small local conformational change that, in turn, could affect C196, one of the three cysteines that link 3Fe-4S, and then disrupt cluster binding. The C93R mutation breaks the ligation of the cluster 2Fe-2S because this cysteine participates in the binding to the prosthetic group. The mutation places a big and charged amino acid that is oriented to FAD-binding protein (chain A). The arginine side chain clashes with H99, A102 (both in chain A), and even the FAD group, thus hampering the chain A-chain B complex association. The C186Y mutation breaks the binding to the cofactor 4Fe-4S. The side chain of tyrosine also clashes with backbone and side chain of L188 and with A210. The P254L mutation must carry a conformational reorganization of the loop because dihedral angles adopted by proline are forbidden for leucine. This conformational change could affect the contiguous C253 and thus the binding of the cluster 4Fe-4S, in which is directly implicated the C253. The side chain of leucine also clashes with backbone and side chain of L111 and T110. Additionally, the P254L mutation could also clash with C191, which in turn affects the C192 and binding to the 4Fe-4S cluster. Figure 3 illustrates the predicted structural-functional consequences behind the pathogenic missense SDHB mutations found in this study. Conformational changes induced by R17L mutation in SDHD structure could not be analyzed because it is located in the signal peptide region, and no structural information was available. The mutation may affect protein transport to the membrane and/or membrane insertion.
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In a second round of analysis, 19 relatives of sporadic patients were investigated for the putative disease-causing mutation found in the respective proband. Genetic screening identified five phenotypically unaffected SDHB mutation carriers and one double, SDHD and SDHB, mutation carrier (Table 2). By the time we closed the study, all six mutated relatives were free of disease.
Sporadic cases harboring germline mutations disclosed features significantly different from those observed in individuals without germline mutations (Table 3). Irrespective of the affected gene, the mutation carriers were mainly males (P = 0.040), with a lower mean age at diagnosis (P = 0.0012). Curiously, SDHB-mutation carriers were younger than SDHD-mutation carriers. The mutated tumors were larger and affected primarily the vagal body. Despite all the SDHD-linked and half of the SDHB-linked cervical PGL patients lived near the sea level or at low altitudes, the residential altitudes were not significantly different between patients with and without germline mutations (62.5 vs. 71%, respectively, lived near the sea level or at low altitudes).
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All four families (F1-F4) carried germline mutations (Table 2). The genealogical trees are depicted in Fig. 4. All but one of the SDHD mutation carriers in whom we could trace the parental origin received the mutation from the father. In line with published data, the only individual who inherited the mutation from the mother remained tumor free by the age of 31 yr.
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In F2, the index case underwent surgery at the age of 42 yr for a right carotid body PGL and a right jugular PGL. Two years later, a left carotid body PGL was removed in the same patient. A brother was also diagnosed of bilateral carotid body PGLs at the age of 42 yr. Both presented a frameshift mutation in SDHD (c.337–340DelGACT), which results in a premature stop codon (p.Asp113MetfsX21) and thus in a truncated protein lacking the last 26 amino acids. This mutation was also detected in three other family members that, so far, have not developed the disease. In addition to the c.337–340DelGACT SDHD mutation, the index case also presented the SDHC IVS1 + 13 InsTG intronic variant.
In F3, the index case underwent surgery twice, at the age of 40 yr for a left carotid body PGL and 15 yr later for a right jugular PGL. A brother was diagnosed of carotid body PGL at the age of 60 yr. Both exhibited an unreported frameshift mutation in SDHD (c.120–127DelCCCAGAAT), which results in a premature stop codon (p.Ile40MetfsX25) that removes 92 amino acids. Three phenotypically unaffected relatives also carried the mutation.
In F4, the index case was diagnosed with a right jugular PGL at the age of 39 yr. His mother had developed a carotid body and a jugulotympanic PGL, being first treated at the age of 43 yr. The other two diseased members were a brother of the index case, deceased at the age of 33 yr, who presented with multiple extraadrenal PGLs 2 yr before and a cousin of the index case, who, at the age of 38 yr, underwent surgery for an extraadrenal PGL. These four patients harbored a missense mutation (C98Y) in a highly conserved residue of SDHB. They also showed the polymorphisms IVS2–36G>T and A6A in SDHB. Three disease-free relatives also disclosed the C98Y mutation. Structural modeling revealed that C98Y mutation may disrupt the enzymatic activity of SDHB because the C98 residue participates in the prosthetic group binding. The mutation hampers the interaction with SDHA and breaks the binding to cluster 2Fe-2S. The Y98 aromatic ring clashes with the 2Fe-2S cluster and also with the neighboring S100, C93 (side chain and backbone), and R94 backbone (Fig. 3B).
The germline mutations found in these four families were confirmed at the somatic level. No additional somatic mutations were detected in any of the affected family members.
Fifty-three percent of SDHD and 43% of SDHB mutation carriers were disease free at the last follow-up annotated in our familial registry. Despite some of the nonaffected at risk carriers might be too young to have clinical manifestations and may develop the disease in their lifetime, our findings suggest incomplete/reduced penetrance of the mutated alleles. Of note, three families had lived near sea level (SDHB-C98Y) or at low average altitudes (SDHD-c.386–387InsT and SDHD-c.337–340DelGACT).
Genotype-phenotype correlation
To evaluate the impact of our results on the routine clinical management of cervical PGL patients, the phenotype of patients with germline mutations was compared with that of patients without germline mutations (Table 4). SDH-mutated tumors occurred predominantly in males (P = 0.0033), occurred at a younger age (P < 0.0001), were usually multifocal (P = 0.0011), and exhibited a larger average size (P = 0.0341). When comparing familial PGLs with occult familial cases, we observed that the former group was significantly associated with tumor multiplicity (P = 0.014).
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Discussion |
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In five sporadic SDH mutation carriers, at least one phenotypically unaffected relative harbored a mutation identical with that shown in the proband, excluding the possibility of considering those alterations as de novo germline mutations. This observation supports the term of occult familial condition given to those sporadic patients who carry pathogenic germline mutations. Of note, the proportion of occult familial cases in our series (22.2%) is higher than the heritability estimates recorded thus far for sporadic presentations in most European and North American series of head and neck PGLs without a founder effect (0–9%) (16, 25, 26, 27, 28, 29). A study performed in 23 sporadic cervical PGLs from Australia revealed a similar percentage (17%) of occult familial conditions; however, half of the patients with germline mutations disclosed the SDHD P81L mutation, which has been associated with a founder effect (13, 30, 31). Single ancestral haplotypes are determinant in cervical PGLs occurring in The Netherlands, where about 36% of the sporadic cases seem to arise as a consequence of three founder/ancestral mutations in SDHD (D92Y, L95P, and L139P) (28, 32). According to the reported absence of a founder/ancestral effect in SDHB among low-altitude inhabitants, in our series we did not observe founder mutations in the SDHB gene.
Another surprising finding of our study was the difference in the mutation frequency of SDHB and SDHD genes, depending on the existence or not of familial disease history. Whereas occult familial cervical PGLs were mainly associated with SDHB mutations, familial cases with proven disease history were mostly associated with SDHD mutations. The causes for the different mutation pattern are unknown. Intrinsic and/or extrinsic modifiers might play a yet undetermined role in the sporadic population analyzed in this study. In addition, the low residential altitudes in 69% of the sporadic cases might have contributed to the high frequency of SDHB mutation carriers. It is believed that environmental oxygen, which is determined by geographical elevations, exerts a major modifier role on the prevalence, penetrance, and phenotypic expression of SDH mutations (14, 33). Low altitudes may reduce gene penetrance and consequently relax the natural selection against SDH mutations, which are therefore able to remain in the population gene pool. Different population-based studies in Dutch inhabitants living near the sea level have shown that, whereas the frequency of germline SDHD mutations increases with successive generations through genetic drift, the likelihood of developing cervical PGLs among at risk mutation carriers does not increase on the same proportion (28, 32).
Our results support the previous observations that germline SDHC mutations are rare among apparently sporadic cervical PGLs (see SDHC@chromium.liacs.nl/lovd_sdh/) (16, 25, 26, 34, 35). In this study, germline SDHB mutations emerged as the leading cause of cervical PGLs. Twelve of 40 sporadic and familial patients (30%) disclosed pathogenic mutations and 58% were in SDHB. Moreover, seven of the 11 different pathogenic mutations (64%) found in our study were located in SDHB. These findings appear to argue against putative anatomical preferences by different SDH subunits as has been formerly suggested (13, 14, 27, 29). Most of the annotated SDHD mutation carriers have been associated with cervical PGLs, contributing to the belief that SDHD dysfunction is the key event in PGLs developing in the head and neck region. Here we provide genetic evidence supporting the involvement of the SDHB subunit in a significant number of cervical PGLs. Whether differences, other than founder/ancestral haplotypes, inherent to the populations analyzed thus far may play a role in the preference of one gene over the other still awaits clarification.
We found no evidence for distant metastases and/or extraparaganglial malignancies in patients with germline SDHB mutations, who were free of disease after an average follow-up period of 7 yr. This observation is in contrast with previous data showing an increased likelihood for tumor recurrence, distant metastases, and/or early onset of renal cell carcinoma or papillary thyroid carcinoma among patients with germline SDHB mutations (29, 36, 37, 38, 39). However, most of these patients had developed intraabdominal extraadrenal PGLs, which tend to be the most aggressive type of PGL (3, 4). In our series, the only two patients who underwent surgery for an intraabdominal extraadrenal PGL belonged to the single family with a SDHB point mutation, and one of them developed multiple extraadrenal PGLs, dying shortly afterward of disease. Strikingly, most of the reported patients harboring malignant SDHB-mutated PGLs, with follow-up information available, had prolonged survival periods, apparently not significantly different from those observed in patients without germline mutations that had metastases at first intervention or during the follow-up (29, 36, 40). Taking all these findings together, it is likely that the hormonal and developmental milieu (head and neck vs. abdominal paraganglia) within which the tumor grows might exert a considerable influence over its molecular biology and natural history and thus be more important than the affected gene (SDHD vs. SDHB).
Our study adds a number of new SDHB and SDHD mutations to those already described (35). In contrast with previous reports, nonsense mutations were not detected among SDHD-linked cervical PGL patients who primarily carried frameshift mutations. In line with published data, missense substitutions were the most common type of mutation among SDHB-linked cervical PGLs. Both frameshift and missense mutations were predicted to result in profound conformational changes in mitochondrial SDH structure, which most likely result in severe SDH dysfunction. All the pathogenic missense SDHB mutations (C93R, C98Y, P197S, C186Y, and P254L), by breaking the binding to the iron-sulfur clusters, may interfere in the electron transfer through the FES, FS4, and F3S clusters present within the catalytic core of SDH. In addition, C93R and C98Y may inhibit the interaction with SDHA and P197L may affect ubiquinone binding, which would also hinder electron entry in the OXPHOS system. Several other lines of evidence provide additional indirect support to the functional relevance of the aforementioned missense SDHB mutations. First, the prevalence of missense mutations in this study was higher than the background mutation frequency of nonfunctional alterations observed in the genome of tumor cells. Second, the residues affected by those mutations are highly conserved during evolution. Third, C93R, C98Y, P197S, C186Y, and P254L were not found in healthy control individuals recruited from the general population. Fourth, the C98Y mutation cosegregated with disease phenotype.
In this study we also demonstrate that occult familial cases and familial cases with proven disease history have a common clinicopathological signature, which distinguishes them from truly sporadic cervical PGL patients without germline SDH mutations. The only feature that distinguished truly familial from occult familial cases was tumor multifocality, which occurred more often in familial cases with proven disease history. Indeed, it has been proposed to consider bilateral or multifocal PGLs as a phenotypical marker for inherited predisposition.
In conclusion, this study highlights the clinical usefulness of genetic testing in all subjects presenting with solitary cervical PGL and no family history. We provide genetic evidence that associates germline SDHB mutations with the pathobiology of a significant number of apparently sporadic cervical PGLs. Moreover, at variance with intraabdominal extraadrenal PGLs, SDHB dysfunction in PGLs of the head and neck region does not appear to entail a deleterious behavior. Our results support the option of offering genetic testing to all at-risk living relatives of sporadic and familial patients harboring a germline mutation. To enable an early detection of affected paraganglia and thus avoid the serious morbidity of surgery in advanced head and neck PGLs, the asymptomatic SDH-mutation carriers should probably be enrolled in a surveillance program.
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Acknowledgments |
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Footnotes |
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Disclosure Statement: The authors have nothing to disclose.
First Published Online September 11, 2007
1 J.L. and T.F. contributed equally to this work. 
Abbreviations: PGL, Paraganglioma; SDH, succinate dehydrogenase; SSCP, single-strand conformation polymorphism analysis.
Received March 21, 2007.
Accepted September 4, 2007.
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  B E Baysal Clinical and molecular progress in hereditary paraganglioma J. Med. Genet., November 1, 2008; 45(11): 689 - 694. [Abstract] [Full Text] [PDF]
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