You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
x - linked severe combined immunodeficiency ( x - scid ) is a rare , life - threatening disease that is characterized by marked impairment of both cellular and humoral immunity ( 1 ) .
human x - scid occurs in as many as 50% of patients with primary scid ; patients have complete or marked deficiency of t cells but carry a normal or slightly increased number of b cells , despite a deficiency in specific antibody responses ( 2 ) .
infants with scid have no tonsils , rarely have detectable peripheral lymph nodes , and have a small , poorly differentiated thymus gland . without bone marrow transplantation ( bmt ) , affected patients suffer severe and persistent infections , often with opportunistic pathogens , and generally die in infancy .
the abnormal gene was mapped to the xq13 region , and later identified as the gene encoding the common gamma ( c ) chain ( 3 , 4 ) that is common to the cell - surface receptors for six interleukin ( il ) molecules ( il-2 , 4 , 7 , 9 , 15 , and 21 ) ( 2 - 5 ) .
based on the amino acid sequence , the complete cdna clone encoding the 64-kda molecule was isolated and demonstrated to be the cognate il-2r chain ( 6 , 7 ) .
the intracellular portion of the c chain is known to interact with janus kinase 3 ( jak3 ) , a signaling kinase that cooperates with other jak and stat proteins in a complex signal transduction array ( 8 , 9 ) .
various mutations in the c chain gene have been reported in patients with x - scid ( 10 - 15 ) .
however , little is known about the clinical and immunological characteristics , or the genetic polymorphism in korean patients with x - scid . here
, we report the mutation identified in one korean family with x - scid , along with prenatal diagnosis of the disease by rflp analysis . to our knowledge
, this is the first report of the molecular diagnosis of x - scid in a korean patient .
a 13-month - old boy was transferred to the department of pediatrics , chonnam national university hospital , because of refractory , progressive pneumonia , and nodular skin lesions . from the age of 7 months
the birth history was not contributory , but there was an infant death history of unknown etiology for his uncle on the mother 's side .
, he was immediately intubated and maintained with an artificial ventilator because of severe , bilateral pneumonia causing respiratory failure .
the blood counts on admission were : white blood cell , 45,100/l ( neutrophil 75.5% , lymphocyte 15.1% ) ; hemoglobin , 14.4 g / dl ; platelets 209,000/l .
his serum immunoglobulin profile was : igg , 27.0 mg / dl ( normal range , 345 - 1,236 mg / dl ) ; igm , 50.4 mg / dl ( 41 - 173 mg / dl ) ; iga , 22.9 mg / dl ( 14 - 159 mg / dl ) .
flow cytometric analysis of lymphocyte immunophenotype was : cd3 t cells , 2.5% ( normal range , 60 - 85% ) ; cd19 b cells , 95.4% ( 8 - 20% ) ; cd16/cd56 natural killer cells , 0.5% .
on physical examination , he had no bcg scar , and biopsy on the nodular skin lesion was later found to be a tuberculous granuloma .
he was treated with broad - spectrum antibiotics , anti - tuberculosis agents , prophylactic antifungal agents , and intravenous globulins .
the recent blood counts without infection were : 5,300/l ( neutrophils , 58.5% ; lymphocytes , 27.4% ) ; hemoglobin , 12.5 g / dl ; platelets 265,000/l .
blood samples were obtained from the patient and various family members with written informed consent .
heparinized venous blood samples from the patient and his family members were fractionated on a ficoll - hypaque gradient to isolate peripheral blood mononuclear cells ( pbmcs ) .
pbmcs were washed twice in pbs and 0.02% nan3 , and analyzed by flow cytometry for c chain expression using the pe - conjugated rat anti - human c chain monoclonal antibody tugh4 ( beckton - dickinson , mountain view , ca , u.s.a . ) .
incubation with unlabeled tugh4 before the addition of labeled tugh4 provided the background control staining .
the method for immunofluorescence staining was the same as that described previously ( 16 ) . as shown in fig .
1b , pbmcs from the mother showed c chain expression on both cd3- and cd19-positive populations .
in contrast , cells from the patient showed a very depressed c chain expression on cd3- and cd19-positive cells , suggesting both t and b cells from the patient did not express c chain on the cell surface ( fig .
the eight exons of the c chain and surrounding genomic sequences were amplified from genomic dna as described previously ( 12 ) . as shown in fig .
2a , we found a single base substitution ( c690 t ) at exon 5 , resulting in an amino acid change at codon 226 ( r226c ) in the patient .
his mother was found to have one mutant and one normal allele , indicating that she was a heterozygous carrier . as the c - to - t substitution predicted the creation of a new alui restriction endonuclease site , the sequencing results
the patient showed dna cleavage with alui ( bands of 179 and 133 bp ) , while the normal control was resistant to alui .
the mother possessed an uncleaved ( 312 bp ) and two smaller bands identical to those in the patient , implying heterozygosity . by rflp analysis
, we were able to perform a prenatal diagnosis on a male fetus . at the 24th week of gestation
, 3 ml of umbilical cord blood was sampled percutaneously , and analyzed for lymphocyte phenotyping .
the fetus had the same t - b+nk- phenotype ( cd3 t cells , 1.2% ; cd19 b cells , 78.6% ; cd16/cd56 natural killer cells , 1.2% ) .
as shown in fig . 2c , the fetal dna showed the same cleaved dna pattern as the patient , while the healthy control dna showed the normal pattern .
rflp analysis demonstrated that the fetus had the same mutation as his brother , and the pregnancy was terminated after lengthy counseling .
the patient is now being cared for at our outpatient clinic , awaiting a stem cell transplant from an alternative donor , because he does not have an hla - matched sibling .
here , we report the first mutation analysis of the c chain gene in a presumed x - scid patient from a korean family . the patient had a single point mutation ( c690 t ) at exon 5 , resulting in an amino acid change at codon 226 ( r226c ) .
the national institutes of health database of c chain mutations lists 264 mutation entries , comprising 169 unique molecular events ( http://www.nhgri.nih.gov/dir/gmbb/scid/il2rgbase.html ) .
mutations have been identified throughout all eight exons of the c chain , the majority of which are missense mutations , nonsense mutations , or splicing defects that give rise to aberrant transcripts . the missense mutation found in this study is not novel .
the available data suggest that the codon 690 may be a hot spot for c chain gene mutation , as reported in several studies ( 10 , 12 - 15 ) .
we did not examine the stability of mrna or protein expression of the c chain in this study , but our previous study demonstrated that the c chain containing the point mutation was not expressed on the cell surface because it was trapped in the golgi apparatus and failed to be transported to the cell surface ( 12 ) .
further identification of the locations and types of mutations in the c chain gene may lead to a better understanding of the functional domains of the protein .
in addition , the patient showed a very little expression of c chain on both b and t cells . in a previous study ,
cell - surface staining of patient - derived b cell lines with an anti-c chain antibody showed no c chain staining in 47% and trace amounts in 32% , but normal intensity of staining in 21% of patients ( 11 ) . in another study , rapid protein analysis with flow cytometry and immunoblotting were shown to be useful for diagnosis of x - scid and jak3-deficient scid .
although the patients had mutations in the c chain gene , some had trace or normal levels of c chain expression .
thus , these proteinbased assays have led to rapid molecular diagnoses of x - scid that have subsequently been confirmed by genetic analysis .
the male x - scid patient in the present study had a classical , severe phenotype , and laboratory data showed low numbers of t cells , relatively well - preserved b cells , and reduced nk cell numbers .
x - scid is a disease that is characterized by severe lymphopenia and recurring persistent infections in the first months of life ( 17 ) .
a human jak3-deficiency disease has similar clinical features to x - scid ( 18 ) , and the c chain and jak3 signaling pathway have been suggested to be crucial for t cell development , and to contribute to the x - scid phenotype ( 18 ) . in addition , gene disruption of either il-7 ( 19 ) or the il-7r subunit ( 20 ) has been shown to lead to severe developmental perturbations .
thus , signaling defects in the il-7/il-7r system resulting from changes in the c chain may account for the developmental anomalies that lead to x - scid .
we also performed a prenatal diagnosis for this family , based on our genetic findings .
most of the primary immunodeficiency diseases can be diagnosed by means of screening for lymphopenia or for t cell deficiency in cord blood at birth .
in addition , fully defining the molecular defects of patients is essential for genetic counseling of family members and prenatal diagnosis . in conclusion
, we described here the molecular and cellular identification of an x - scid patient in a korean family .
our data emphasize that flow cytometric analysis is an important and powerful assay that can contribute to diagnosis of x - scid .
further studies of x - scid mutations should be compiled and analyzed to provide data to clarify the correlation between the severity of the disease and the types and locations of the mutations in x - scid patients .
x - linked severe combined immunodeficiency ( x - scid ) is a rare , life - threatening immune disorder , caused by mutations in the c chain gene , which encodes an essential component of the cytokine receptors for interleukin-2 ( il-2 ) , il-4 , il-7 , il-9 , il-15 , and il-21 . a 13-month - old boy with recurrent infections who had reduced serum immunoglobulin levels and decreased numbers of cd3 
 , cd16/56 cells was evaluated for c chain gene mutation and protein expression . 
 the patient had a c - to - t point mutation at nucleotide position 690 , one of the hot spots , resulting in a single amino acid substitution of cysteine for arginine ( r226c ) , as determined by direct sequencing and pcr - rflp . 
 the patient 's mother was a heterozygous carrier . 
 percutaneous umbilical cord blood sampling was performed at the 6-month of gestation in a subsequent pregnancy . 
 as the immunophenotype of the fetus showed an identical pattern , the pregnancy was terminated and genetic analysis of the abortus confirmed recurrence . 
 this is the first report of the molecular diagnosis of x - scid in korea . 
 genetic analysis of the c chain gene is useful for definite diagnosis and genetic counseling for x - scid .