|
||
BRIEF DEFINITIVE REPORT |
gene in the X chromosome pseudoautosomal region 1
CORRESPONDENCE David P. Huston: dhuston{at}medicine.tamhsc.edu
|
|
|---|
chain, encoded in the X-chromosome pseudoautosomal region 1.
Pulmonary alveolar proteinosis (PAP) is a rare disorder of the lung caused by impaired surfactant homeostasis and is clinically characterized by the accumulation of lipoproteinaceous material within alveolar spaces, often leading to respiratory failure (1). Three forms of PAP have been described: congenital, secondary, and acquired. Congenital PAP can result from mutations in genes encoding the surfactant proteins B or C, or the common β chain (βc) of the receptor for GM-CSF (2–6). Secondary PAP develops in conditions in which there are reduced numbers or functional impairment of pulmonary alveolar macrophages, and has been associated with the inhalation of inorganic dust (silica) or toxic fumes, hematologic malignancies, pharmacologic immunosuppression, certain infections, and impaired βc expression (7–11). Acquired PAP is the most common form, usually occurring in adults, and is caused by neutralizing autoantibodies to GM-CSF (12–14).
The importance of GM-CSF in the pathogenesis of PAP has been confirmed in humans and mice, wherein GM-CSF signaling is required for pulmonary alveolar macrophage catabolism of surfactant (12–17). In addition, mice with a targeted disruption of GM-CSF or βc genes developed PAP (15–17). Local expression of GM-CSF in the lungs of GM-CSF–deficient mice, or transplantation of bone marrow from normal mice into βc-deficient mice, corrected the defective metabolism of surfactant (18–19). Furthermore, administration of GM-CSF has been efficacious in some patients with acquired PAP (20).
Because the GM-CSFR is composed of a cytokine-binding GM-CSFR
Lack of GM-CSFR
chain (GM-CSFR
) subunit and the βc subunit (21,22), theoretically, deficiency of either subunit should have the potential to result in PAP. We provide the first report that PAP can result from a genetic deficiency of the GM-CSFR
.
![]()
RESULTS AND DISCUSSION
Top
ABSTRACT
RESULTS AND DISCUSSION
MATERIALS AND METHODS
REFERENCES
Case history
A 4-yr-old female with Turner syndrome and respiratory insufficiency was diagnosed with PAP at age 3. Her past history was significant for respiratory failure caused by respiratory syncytial virus pneumonia in the first month of life, and a diagnosis of reactive airways disease. She presented with respiratory distress and hypoxemia, with a "crazy paving" pattern on chest imaging. Open lung biopsy revealed alveolar proteinaceous material without alveolar epithelial hyperplasia or chronic interstitial changes, and bronchoalveolar lavage revealed proteineous material and foamy macrophages, all of which are consistent with PAP. Analyses for mutations of the genes encoding surfactant proteins B and C and ABCA3 were negative (performed by the Johns Hopkins DNA Diagnostic Laboratory). Her serum GM-CSF concentration measured by ELISA (performed by the University of Michigan Cytokine Reference Laboratory) was 1,573.3 pg/ml (normal = 0–7.8 pg/ml), and anti–GM-CSF antibody concentration measured by ELISA (performed by the Cleveland Clinic Cytokine Biology Laboratory) was 0 ng/ml. Her complete blood count and differential were normal. Worsening respiratory failure was managed intermittently by whole lung saline lavage under arteriovenous extracorporeal membrane oxygenator support, but pulmonary function progressively declined. Treatment with 20 µg/kg GM-CSF per day subcutaneously, which may be efficacious in some patients with acquired PAP (20), was not beneficial. Given the absence of surfactant gene mutations and anti–GM-CSF antibodies, the elevated baseline GM-CSF serum levels and the lack of clinical improvement with exogenous GM-CSF administration, and no evidence for other secondary causes of PAP, the potential for a defect in the GM-CSFR was investigated.
expression and function in the patient's monocytes
To test the hypothesis that the patient had a defect in GM-CSFR expression, flow cytometry was used to detect GM-CSFR
and βc on peripheral blood monocytes of the patient, as well as her father, mother, and sister. The mother expressed high levels of GM-CSFR
on virtually all of her monocytes, as demonstrated in Fig. 1 A by the single peak of staining on her CD14+ cells, as expected (23).
In contrast, GM-CSFR
was undetectable on the patient's monocytes (Fig. 1 A). By comparison, the father and sister demonstrated bimodal patterns of GM-CSFR
expression on their monocytes (Fig. 1 A), indicating that only a subpopulation of the father's and the sister's monocytes expressed GM-CSFR
. All subjects expressed cell-surface βc (unpublished data), and βc function in the patient was indicated by the presence of normal numbers of peripheral blood eosinophils, which differentiate in response to IL-5 signal transduction through the IL-5R
and βc (24).
|
expression by the patient was accompanied by functional unresponsiveness to GM-CSF, GM-CSF–induced up-regulation of CD11b on granulocytes of the patient and her mother were measured by flow cytometry (Fig. 1 B), as previously described (25). Constitutive expression of CD11b was greater on the mother's granulocytes (mean fluorescence intensity [MFI] = 6,337) than the patient's granulocytes (MFI = 4,347). The mother's granulocytes had a 22.4 stimulation index (SI) with 50 ng/ml GM-CSF (MFI = 7,759) and a 34.1 SI with 100 ng/ml GM-CSF (MFI = 8,498). In contrast, the patient's granulocytes did not up-regulate CD11b in response to GM-CSF, with a –1.2 SI at 50 ng/ml GMCSF (MFI = 4,294) and a –11.6 SI at 100 ng/ml GM-CSF (MFI = 3,841).
Absence of GM-CSFR
mRNA transcripts by the patient's leukocytes
The patient's karyotype indicated a 46Xi(Xq) genotype in which the Xi chromosome appeared to be of normal length and hybridized a probe for the X-chromosome pseudoautosomal region 1 (X-PAR1) region (Fig. 2 A).
In contrast, the Xq chromosome had a truncated Xp arm and did not hybridize the X-PAR1 probe.
|
protein expression was accompanied by impaired expression of GM-CSFR
mRNA transcripts, RT-PCR was used. For comparison, transcripts were also amplified for βc and the other βc-associated receptor molecules (IL-3R
and IL-5R
), as well as mRNA transcripts from genes flanking the GM-CSFR
gene within the X-PAR1 region (thymic stromal lymphopoietin receptor [TSLPR] and acetylserotonin methyltransferase [ASMTL]). Results from the patient's leukocytes were compared with results from her family members and an unrelated healthy control (Fig. 2 B). The patient's family members and the control subject each expressed all of the transcripts. In contrast, transcripts for GM-CSFR
and IL-3R
were not detected for the patient, whereas the other transcripts were detected. These data suggested a potential defect in the patient's X-PAR1 that affected both the GM-CSFR
and IL-3R
genes.
Deletion of the patient's GM-CSFR
exons 5–13
To directly analyze the integrity of the GM-CSFR
gene structure, PCR amplification of each of the 11 exons encoding GM-CSFR
(exons 3–13) was performed (Fig. 3).
In addition, a primer set for exon 8 of the SMG1 gene on chromosome 16 was included as an internal PCR control (627 bp). Results with the patient's DNA were compared with those with DNA from three control cell lines. Although all 11 coding exons of GM-CSFR
were detected in each of the controls, only the first two coding exons (exons 3 and 4) of GM-CSFR
were detected in the patient's DNA; exons 5–13 were absent.
|
. Clinical expression of PAP caused by a genetic deficiency of GM-CSFR
would predictably require homozygous defects involving both of the GM-CSFR
alleles. However, because the GM-CSFR
gene is encoded in the PAR1 region of the X and Y chromosomes (26), Turner syndrome, which is caused by the absence or partial deletion of one of the X chromosomes (27), provides the biological circumstance of nature whereby a defect in one GM-CSFR
allele could result in the PAP phenotype.
The absence of mRNA transcripts for GM-CSFR
and IL-3R
indicated that the PAR1 region of the Xi chromosome was abnormal, despite the positive hybridization signal from the fluorescence in situ hybridization (FISH) experiment. The presence of mRNA transcripts for TSLPR and ASMTL, whose genes flank the genes for GM-CSFR
and IL-3R
, respectively, suggested a genomic deletion that affected
1 mb. Examination of the 11 coding exons for GM-CSFR
demonstrated deletion of exons 5–13, providing a genetic basis for the absence of mRNA transcripts and protein for GM-CSFR
. Because the IL-3R
message was not detected in the patient, the genetic deletion affecting GM-CSFR
likely extends to the gene encoding IL-3R
. However, impaired IL-3 responses do not result in a PAP phenotype in mice (17) and have not been associated with PAP in humans.
Although the bimodal pattern of GM-CSFR
protein expression by the patient's father and sister was not accompanied by a clinical phenotype, this raises the possibility that both the father and sister are carriers of a PAR1 partial deletion. If so, then such a deletion resides on the paternal X-PAR1, and not on the Y-PAR1, and would be consistent with the patient's Xi being of paternal origin. Alternatively, the patient's Xi-PAR1 deletion may have occurred de novo in the context of recombination and genomic rearrangement that resulted in the Turner genotype.
The PAR1 is essential for meiotic pairing and recombination of sex chromosomes (26, 28). Although all genes within the PAR1 escape X inactivation and are therefore candidates for haploinsufficiency disorders, the only previously known disease gene within the PAR1 is the short-stature homeobox (28). Although the PAR1 has a high frequency of recombination, the subregion encoding the GM-CSFR
gene apparently has a relatively low level of recombination (28). The frequency of mutations in GM-CSFR
that impair physiological responses to GM-CSF is unknown, but is likely to be rare even in large populations because the prevalence of PAP is low. However, the potential importance of GM-CSF responsiveness for granulocyte and pulmonary alveolar macrophage function leaves open the possibility that some degree of immune dysfunction could occur in the context of partial unresponsiveness to GM-CSF. Indeed, the recent demonstration of an impaired ability of granulocytes to respond to GM-CSF in autoimmune PAP (25) was confirmed in our patient by the inability of her granulocytes to up-regulate expression of CD11b after GM-CSF stimulation. Moreover, the immediate adjacency of the genes for TSLPR, GM-CSFR
, and IL-3R
, all of which encode for receptors of relevance to allergic inflammation, also raises the intriguing possibility that mutations within this PAR1 region may have implications for the pathophysiology of allergic disorders.
The importance of GM-CSF signaling in PAP is underscored by the experimental observation that mice with a targeted disruption of GM-CSF or βc genes developed PAP (15–17). In addition, local expression of GM-CSF in the lungs of GM-CSF–deficient mice, or transplantation of bone marrow from normal mice into βc-deficient mice, corrected the defective metabolism of surfactant (18–19). GM-CSFR
–deficient mice have not been reported.
Diagnosing PAP caused by a genetic deficiency of GM-CSFR
has important therapeutic implications because, theoretically, bone marrow reconstitution from a healthy donor should result in leukocytes that express the GM-CSFR
and thereby a cure for the impaired surfactant homeostasis that underlies PAP, especially because such a strategy has been successfully demonstrated in mice with βc deficiency (19). Our patient underwent bone marrow reconstitution with an HLA-matched unrelated donor but died from a respiratory infection 4 wk after transplant, before recovery of immune competency. Nonetheless, the ability to screen for GM-CSFR
deficiency by flow cytometry provides a convenient test for evaluating infants with PAP not explained by other causes of GM-CSF unresponsiveness, and can be confirmed by molecular methods.
| MATERIALS AND METHODS |
|---|
|
|
|---|
Flow cytometry.
GM-CSFR
cell-surface expression on peripheral blood monocytes was analyzed on a flow cytometer (model XL; Beckman Coulter). Monocytes were identified using mouse mAb anti–human CD14–Alexa Fluor 488 (M5E2; BD). GM-CSFR
expression on monocytes was detected using mouse IgG1 mAb anti–human GM-CSFR
(4H1; Santa Cruz Biotechnology, Inc.) and rat mAb anti–mouse IgG1-PE. Background was determined using an isotype-matched negative control mAb (MOPC-21; BD). Data were analyzed using Summit software (Dako).
GM-CSF up-regulation of CD11b expression.
Peripheral blood granulocytes were analyzed by flow cytometry for GM-CSF up-regulation of CD11b expression, as previously described (25), using mouse mAb anti–human CD11b (ICRF44; BD). In brief, freshly isolated white blood cells were either unstimulated or stimulated in vitro with 50–100 ng/ml human GM-CSF for 30 min. Cells were labeled with anti-CD11b–PE antibodies and gated on the granulocyte population, and CD11b expression was measured by flow cytometry. The GM-CSF–induced CD11b SI on granulocytes was calculated by taking the MFI of CD11b on GM-CSF–stimulated granulocytes minus the MFI of CD11b on unstimulated granulocytes, divided by the MFI of CD11b on unstimulated granulocytes, multiplied by 100, as previously described (25). Data were plotted using Excel software (Microsoft).
Karyotype and FISH analysis.
High-resolution G-banded metaphase chromosome analysis was performed on the patient's peripheral blood lymphocytes. FISH was performed to detect the proximal region of the X-PAR1 using bacterial artificial chromosome (BAC) probe RP11-74L17, which hybridizes at 1.781–1.929 mb on Xp22.3. X chromosomes were identified using a BAC probe specific for the X centromere. Miniprep BAC DNA (100 ng) was labeled with Spectrum Orange-dUTP or Spectrum Green-dUTP (Vysis) and used as probes for FISH analysis, as previously described (29).
RT-PCR.
Total RNA was extracted from peripheral blood leukocytes from the patient, family members, and an unrelated healthy control using the RNeasy Mini kit (QIAGEN). 3 µg of total RNA was reverse transcribed with Oligo dT primers using the SuperScript III First-Strand Synthesis System for RT-PCR (Invitrogen). 1 µl of the cDNA reaction was used to amplify each cytokine receptor and control gene with specific primers, for 35 cycles. PCR amplification conditions were as follows: 5 min at 95°C for 1 cycle; 45 s at 94°C for 35 cycles; 1 min at 60°C for 1 cycle; 2 min at 72°C for 1 cycle; and 12 min at 70°C for a final cycle (GeneAmp 9700 PCR System; Applied Biosystems). PCR products were analyzed in a 1% (wt/vol) agarose gel containing ethidum bromide and were visualized by fluorescence. The PAP patient is missing mRNA transcripts for GM-CSFR
and IL-3R
. Primer sequences are listed in Table S1 (available at http://www.jem.org/cgi/content/full/jem.20080759/DC1).
Amplification of the GM-CSFR
gene.
Primer sets flanking each of the 11 coding exons (exons 3–13) of the GM-CSFR
(CSF2RA) gene were individually amplified. A primer set for exon 8 of the SMG1 gene on chromosome 16 was used as an internal PCR standard. Each GM-CSFR
exon primer set was designed to generate amplicons of 200–489 bp, whereas the internal standard was 627 bp. Amplification of the patient's DNA and DNA from three normal control cell lines was performed with Multiplex mix (QIAGEN) using standard PCR conditions. A positive and a negative control for the PCR process were also performed using primers flanking exon 10 of the ARAF gene on chromosome X and cell-line DNA (lanes +/–). Reactions were performed using 10 ng of each DNA, 3.2 pmol of each primer, and 40 cycles of amplification. Each sample was resolved by loading 4 µl of PCR product on a 2% agarose gel and was visualized by ethidium bromide fluorescence. The sizing ladder consists of both HaeIII-digested
X174DNA and HindIII-digested
DNA. Primer sequences are listed in Table S2 (available at http://www.jem.org/cgi/content/full/jem.20080759/DC1).
Online supplemental material.
Primer sequences for RT-PCR of mRNA transcripts and for GM-CSFR
exons are provided in Tables S1 and S2, respectively. Online supplemental material is available at http://www.jem.org/cgi/content/full/jem.20080759/DC1.
| Acknowledgments |
|---|
This work was supported by grants from the National Institutes of Health (AI063178 to M. Martinez-Moczygemba, and AI36936 and AI071130 to D.P. Huston).
The authors have no conflicting financial interests.
Submitted: 9 April 2008
Accepted: 8 October 2008
| REFERENCES |
|---|
|
|
|---|
1 Trapnell, B.C., J.A. Whitsett, and K. Nakata. 2003. Pulmonary alveolar proteinosis. N. Engl. J. Med. 349:2527–2539.
2 Hamvas, A., F.S. Cole, and L.M. Nogee. 2007. Genetic disorders of surfactant proteins. Neonatology. 91:311–317.[CrossRef][Medline]
3 Nogee, L.M., A.E. Dunbar III, S.E. Wert, F. Askin, A. Hamvas, and J.A. Whitsett. 2001. A mutation in the surfactant protein C gene associated with familial interstitial lung disease. N. Engl. J. Med. 344:573–579.
4 Nogee, L.M., G. Garnier, H.C. Dietz, L. Singer, A.M. Murphy, D.E. deMello, and H.R. Colton. 1994. A mutation in the surfactant protein B gene responsible for fatal neonatal respiratory disease in multiple kindreds. J. Clin. Invest. 93:1860–1863.[Medline]
5 Nogee, L.M., D.E. deMello, L.P. Dehner, and H.R. Colten. 1993. Deficiency of pulmonary surfactant protein B in congenital alveolar proteinosis. N. Engl. J. Med. 328:406–410.
6 Dirksen, U., R. Nishinakamura, P. Groneck, U. Hattenhorst, L. Nogee, R. Murray, and S. Burdach. 1997. Human pulmonary alveolar proteinosis associated with a defect in GM-CSF/IL-3/IL-5 receptor common beta chain expression. J. Clin. Invest. 100:2211–2217.[Medline]
7 Rubin, E., G.L. Weisbrod, and D.E. Sanders. 1980. Pulmonary alveolar proteinosis: relationship to silicosis and pulmonary infection. Radiology. 135:35–41.
8 Ruben, F.L., and T.S. Talamo. 1986. Secondary pulmonary alveolar proteinosis occurring in two patients with acquired immune deficiency syndrome. Am. J. Med. 80:1187–1190.[CrossRef][Medline]
9 Abdul Rahman, J.A., U.P. Moodley, and M.J. Phillips. 2004. Pulmonary alveolar proteinosis associated with psoriasis and complicated by mycobacterial infection: successful treatment with granulocyte-macrophage colony stimulating factor after a partial response to whole lung lavage. Respirology. 9:419–422.[CrossRef][Medline]
10 Cordonnier, C., J. Fleury-Feith, E. Escudier, K. Atassi, and J.F. Bernaudin. 1994. Secondary alveolar proteinosis is a reversible cause of respiratory failure in leukemic patients. Am. J. Respir. Crit. Care Med. 149:788–794.[Abstract]
11 Dirksen, U., U. Hattenhorst, P. Schneider, H. Schroten, U. Göbel, A. Böcking, K.M. Müller, R. Murray, and S. Burdach. 1998. Defective expression of granulocyte-macrophage colony-stimulating factor/interleukin-3/interleukin-5 receptor common beta chain in children with acute myeloid leukemia associated with respiratory failure. Blood. 92:1097–1103.
12 Kitamura, T., N. Tanaka, J. Watanabe, K. Uchida, S. Kanegasaki, Y. Yamada, and K. Nakata. 1999. Idiopathic pulmonary alveolar proteinosis as an autoimmune disease with neutralizing antibody against granulocyte/macrophage colony-stimulating factor. J. Exp. Med. 190:875–880.
13 Bonfield, T.L., D. Russell, S. Burgess, A. Malur, M.S. Kavuru, and M.J. Thomassen. 2002. Autoantibodies against granulocyte macrophage colony-stimulating factor are diagnostic for pulmonary alveolar proteinosis. Am. J. Respir. Cell Mol. Biol. 27:481–486.
14 Uchida, K., K. Nakata, B.C. Trapnell, T. Terakawa, E. Hamano, A. Mikami, I. Matsushita, J.F. Seymour, M. Oh-Eda, I. Ishige, et al. 2004. High-affinity autoantibodies specifically eliminate granulocyte-macrophage colony-stimulating factor activity in the lungs of patients with idiopathic pulmonary alveolar proteinosis. Blood. 103:1089–1098.
15 Stanley, E., G.J. Lieschke, D. Grail, D. Metcalf, G. Hodgson, J.A.M. Gall, D.W. Maher, J. Cebon, V. Sinickas, and A.R. Dunn. 1994. Granulocyte/macrophage colony-stimulating factor-deficient mice show no major perturbation of hematopoiesis but develop a characteristic pulmonary pathology. Proc. Natl. Acad. Sci. USA. 91:5592–5596.
16 Robb, L., C. Drinkwater, D. Metcalf, R. Li, F. Köntgen, N.A. Nicola, and C.G. Begley. 1995. Hematopoietic and lung abnormalities in mice with a null mutation of the common beta subunit of the receptors for granulocyte-macrophage colony-stimulating factor and interleukins 3 and 5. Proc. Natl. Acad. Sci. USA. 92:9565–9569.
17 Nishinakamura, R., N. Nakayama, Y. Hirabayashi, T. Inoue, D. Aud, T. McNeil, S. Azuma, S. Yoshida, Y. Toyoda, K. Arai, et al. 1995. Mice deficient for the IL-3/GM-CSF/IL-5 βc receptor exhibit lung pathology and impaired immune response, while βIL-3 receptor-deficient mice are normal. Immunity. 2:211–222.[CrossRef][Medline]
18 Zsengeller, Z.K., J.A. Reed, C.J. Bachurski, A.M. LeVine, S. Forry-Schaudies, R. Hirsh, and J.A. Whitsett. 1998. Adenovirus-mediated granulocyte-macrophage colony-stimulating factor improves lung pathology of pulmonary alveolar proteinosis in granulocyte-macrophage colony-stimulating factor-deficient mice. Hum. Gene Ther. 9:2101–2109.[Medline]
19 Nishinakamura, R., R. Wiler, U. Dirksen, Y. Morikawa, K. Arai, A. Miyajima, S. Burdach, and R. Murray. 1996. The pulmonary alveolar proteinosis in granulocyte macrophage colony-stimulating factor/interleukins 3/5 beta c receptor-deficient mice is reversed by bone marrow transplantation. J. Exp. Med. 183:2657–2662.
20 Venkateshiah, S.B., T.D. Yan, T.L. Bonfield, M.J. Thomassen, M. Meziane, C. Czich, and M.S. Kavuru. 2006. An open-label trial of granulocyte macrophage colony stimulating factor therapy for moderate symptomatic pulmonary alveolar proteinosis. Chest. 130:227–237.[CrossRef][Medline]
21 Gearing, D.P., J.A. King, N.M. Gough, and N.A. Nicola. 1989. Expression cloning of a receptor for human granulocyte-macrophage colony-stimulating factor. EMBO J. 8:3667–3676.[Medline]
22 Hayashida, K., T. Kitamura, D.M. Gorman, K. Arai, T. Yokota, and A. Miyajima. 1990. Molecular cloning of a second subunit of the receptor for human granulocyte-macrophage colony-stimulating factor (GM-CSF): reconstitution of a high-affinity GM-CSF receptor. Proc. Natl. Acad. Sci. USA. 87:9655–9659.
23 Jubinsky, P.T., A.S. Laurie, D.G. Nathan, J. Yetz-Aldepe, and C.A. Sieff. 1994. Expression and function of the human granulocyte-macrophage colony-stimulating factor receptor alpha subunit. Blood. 84:4174–4185.
24 Martinez-Moczygemba, M., and D.P. Huston. 2003. Biology of common beta receptor-signaling cytokines: IL-3, IL-5, and GM-CSF. J. Allergy Clin. Immunol. 112:653–665.[CrossRef][Medline]
25 Uchida, K., D.C. Beck, T. Yamamoto, P.Y. Berclaz, S. Abe, M.K. Staudt, B.C. Carey, M.D. Filippi, S.E. Wert, and L.A. Denson. 2007. GM-CSF autoantibodies and neutrophil dysfunction in pulmonary alveolar proteinosis. N. Engl. J. Med. 356:567–579.
26 Kremer, E., E. Baker, R.J. D'Andrea, R. Slim, H. Phillips, P.A. Moretti, A.F. Lopez, C. Petit, M.A. Vadas, G.R. Sutherland, et al. 1993. A cytokine receptor gene cluster in the X-Y pseudoautosomal region? Blood. 82:22–28.
27 Sagi, L., N. Zuckerman-Levin, A. Gawlik, L. Ghizzoni, A. Buyukgebiz, Y. Rakover, T. Bistritzer, O. Admoni, A. Vottero, O. Baruch, et al. 2007. Clinical significance of the parental origin of the X chromosome in turner syndrome. J. Clin. Endocrinol. Metab. 92:846–852.
28 Blaschke, R.J., and G. Rappold. 2006. The pseudoautosomal regions, SHOX and disease. Curr. Opin. Genet. Dev. 16:233–239.[CrossRef][Medline]
29 Trask, B.J. 1991. Fluorescence in situ hybridization: applications in cytogenetics and gene mapping. Trends Genet. 7:149–154.[Medline]
Related Article
mutations disrupt surfactant homeostasis
This article has been cited by other articles:
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| TABLE OF CONTENTS |
|