May 2011

Editor:
Michael Bissell, MD, PhD, MPH

• Newborn screening for severe combined immunodeficiency
• Role of cytogenetics in child psychiatry
• Usefulness of CSF cystatin C
• Relationship between serum CA-125 and bone density

Newborn screening for severe combined immunodeficiency

Severe combined immunodefici­ency screening presents an opportunity for newborn screening because this condition, when detected in early infancy, can be treated with bone marrow transplant. The only available screening tool for T-cell deficiencies, such as severe combin­ed immunodeficiency (SCID), is the T-cell re­ceptor excision circle (TREC) assay. However, the TREC assay has drawbacks because it is a first-tier screening assay using DNA and molecular technology, which is not universally adopted by the newborn screening community. Low or absent T cells are a major characteristic of SCID and other T-cell immunodeficiencies. Because there are two case reports of CD3 deficiency causing T-cell immunodeficiency, and because CD3 is part of the T-cell receptor complex on mature T cells, it was surmised that CD3 could be used as a marker for the presence or absence of T cells. CD45 is a common antigen present on all differentiated leukocytes and serves as the internal control in this assay. Immunoassays are used routinely in newborn screening as first-tier screening protocols and can be multiplexed on certain platforms to include several biomarkers. The authors reported on the technical feasibility of detecting T-cell immunodeficiency using a multiplex immunoassay that simultaneously quantifies T cells and total leukocytes in a single 3-mm punch from a Guthrie specimen. They used the multiplexing capabilities of the Luminex platform for their study. Antibody pairs were employed to capture and detect CD3 and CD45 from a single 3-mm punch of the Guthrie specimen. The assay for each biomarker was developed separately using identical buffers and then combined to create a multiplex assay (CD345). Using calibrators made from known amounts of leukocytes, the authors obtained a detection limit of 0.25 × 10⁶ cells/mL for CD3 and 0.l25 × 10⁶ cells/mL for CD45. Affinity tests showed no cross-reactivity between the antibodies to CD3 and CD45. The multiplex assay was validated against eight coded specimens of known clinical status and linked to results from the TREC assay that had identified them. All specimens were correctly identified by the CD345 assay. The authors concluded that the performance parameters of the CD345 assay met the performance characteristics generally accepted for immunoassays. The authors’ assay classifications for positive specimens concurred with previous TREC results. The CD345 as­say warrants evaluation as a viable alternative or complement to the TREC assay as a primary screening tool for detecting T-cell immunodeficiencies, including SCID, in Guthrie specimens.

Janik DK, Lindau-Shepard B, Comeau AM, et al. A multiplex immunoassay using the Guthrie specimen to detect T-cell deficiencies including severe combined immunodeficiency disease. Clin Chem. 2010;56:1460–1465.

Correspondence: Kenneth A. Pass at kpass@wadsworth.org

Role of cytogenetics in child psychiatry

Study of variation in the structure of human chromosomes has made fundamental contributions to the understanding of developmental neuropsychiatric disorders. Once a tool primarily to identify the genetic underpinning of rare and so-called simple Mendelian disorders, particularly mental retardation syndromes, chromosomal analysis has evolved to be a critically important part of the armamentarium used to dissect the genetics of common, multigenic syndromes, such as autism, adult- and childhood-onset schizophrenia, Tourette syndrome, and obsessive-compulsive disorder. The development of tools that allow for high-resolution examination of chromosomal structure have challenged fundamental dogma regarding the nature of “normal” genetic variation, contributed to a re-evaluation of widely held beliefs about the underlying genetic architecture of neuropsychiatric disorders, forced a re-examination of notions regarding the loss of chromosomal material and causality with regard to developmental anomalies, and resulted in forays into clinical genetic diagnoses of complex neuropsychiatric conditions, particularly autism. The authors conducted a study that considered the impact of chromosomal studies on the understanding of childhood neuropsychiatric syndromes, highlighting key discoveries, advances in technology, and new challenges faced by clinicians trying to interpret the recent wave of findings. The authors reviewed the literature on the genetics of child psychiatric disorders, including autism, childhood-onset schizophrenia, attention-deficit/hyperactivity disorder, and Tourette syndrome, with a focus on studies of chromosomal structure. They found that over several decades, cytogenetic investigations have led to key findings relevant to child psychiatry. During this time, technology has transitioned from light microscopy, to molecular cytogenetics, to microarray-based detection of structural variation, resulting in a dramatic increase in the resolution of such approaches. Each of these methods has contributed to understanding the genetic bases of developmental neuropsychiatric disorders. Moreover, implementation of microarray technology has prompted a reconceptualization of the nature of human genetic variation, demonstrating that the sequence of DNA and the fine structure of chromosomes vary in affected and unaffected individuals. The authors concluded that the study of chromosomal variation at high resolution continues to be a promising area of research that is yielding critical data regarding the genetic underpinnings of childhood psychiatric disorders. Preliminary data indicate that apparently identical submicroscopic variations in chromosomal structure may predispose to a broad range of phenotypes. These findings suggest that disruption of the same basic neurodevelopmental mechanisms, such as synapse function, may result in outcomes that span a broad range of psychiatric diagnoses listed in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders.

Hoffman EJ, State MW. Progress in cytogenetics: implications for child psychopathology. J Am Acad Child Adolescent Psych. 2010;49:736–751.

Correspondence: Matthew W. State at matthew.state@yale.edu

Usefulness of CSF cystatin C

Amyotrophic lateral sclerosis is a fatal disorder characterized by generalized skeletal muscle weakness and atrophy due to the degeneration of upper and lower motor neurons. Only a small proportion of amyotrophic lateral sclerosis (ALS) cases (five to 10 percent) have a family history of the disease, and this subset of patients is classified as familial ALS (FALS). A number of disease-causing mutations have been identified in FALS patients, but the etiology of sporadic ALS, which accounts for the majority of cases, remains largely unknown. A number of cytoplasmic protein aggregations, such as Bunina bodies, skein-like inclusions, and Lewy-body–like hyaline inclusions, are observed in sporadic ALS. Both skein-like and Lewy-body–like inclusions are positive for ubiquitin and TDP-43, whereas Bunina bodies are negative for these two proteins. In contrast, Bunina bodies are positive for cystatin C, a cysteine protease inhibitor. Bunina bodies are thought to be the most specific histological marker of sporadic ALS. A recent report showed that Bunina bodies and TDP-43–positive inclusions are visible within the same motor neuron in ALS patients, suggesting there may be a link in the appearance of both types of inclusion in motor neurons undergoing degeneration. When employing proteomic analyses, the cystatin C level was found to be decreased in the cerebrospinal fluid (CSF) of ALS cases, raising concerns about cystatin C as a biomarker of ALS. The authors conducted a study in which they quantified the CSF levels of cystatin C in normal controls and patients with various neurological disorders and determined whether cystatin C levels correlated with the genotype. Using a latex turbidimetric immunoassay, they quantified levels of cystatin C in CSF from 130 age-matched individuals with either a neurological disorder such as ALS, Alzheimer disease, Parkinson’s disease, tauopathy, multiple system atrophy, or chronic inflammatory demyelinating polyneuropathy (CIPD), or with no known neurological condition (normal control). The cystatin C level in CSF was found to correlate with age during the investigation but not with the protein concentration. No difference in cystatin C levels were noted between normal controls and ALS or CIPD cases, whereas cystatin C levels were significantly lower in those with multiple system atrophy compared with normal controls. Of the 130 cases, 96 were genotyped, and G/A or A/A polymorphism at +73 within the CST3 gene was found in 28 individuals. The cystatin C level was significantly lower in the combined group of G/A and A/A genotypes compared with G/G. The data demonstrate that the level of cystatin C in CSF should not be considered a biomarker of ALS, but a correlation does exist between cystatin C levels and the CST3 genotype.

Yamamoto-Watanabe Y, Watanabe M, Jackson M, et al. Quantification of cystatin C in cerebrospinal fluid from various neurological disorders and correlation with G73A polymorphism in CST3. Brain Res. 2010;1361:140–145.

Correspondence: Mitsunori Watanabe at miwata36@cc.hirosaki-u.ac.jp

Relationship between serum CA-125 and bone density

Osteoporosis is an imbalance in the remodeling process in which bone resorption exceeds bone formation. A growing understanding of this process has shown that factors involved in inflammation are linked with those factors critical for bone physiology and remodeling. Pro-inflammatory cytokines, which are critical mediators of inflammatory responses, have also been shown to regulate bone metabolism, even in individuals without immunological diseases. Moreover, the association of bone loss with systemic inflammation is supported because serum high-sensitivity C-reactive protein (hsCRP), a sensitive marker of chronic low-grade systemic inflammation, is a significant predictor of osteoporotic fractures. Tumor-associated antigens (TAAs), such as carcinoembryonic antigen (CEA), carbohydrate antigen (CA) 19-9, and CA-125, may be expressed by inflammatory leukocytes apart from tumor cells. In the soluble form, TAAs may be readily detected in the sera of patients with various autoimmune inflammatory diseases. Based on the potential association of TAAs with systemic inflammation, the authors determined whether high-normal TAA levels are associated with lower bone mineral density levels in otherwise healthy pre- and post-menopausal women. They conducted a study involving 3,769 healthy women enrolled from the health screening program of the Korea University Medical Center over five years. Each participant had undergone a basic health examination. The authors evaluated CA-125, CA 19-9, CEA, and alpha-fetoprotein levels as tumor markers. They analyzed the correlations between serum TAA levels and bone mineral density. The authors found that CA-125 and CEA levels were positively associated with a higher bone mineral density in premenopause. In postmenopause, the CA-125 level was positively associated with bone mineral density. In premenopause, CA-125 (r=0.102; P<0.001) and CEA levels (r=0.134; P<0.001) had a significant correlation with bone mineral density. In postmenopause, CA-125 was negatively associated with alkaline phosphatase (r=–0.298; P<0.001). The authors concluded that a significant positive association exists between CA-125 and bone mineral density in healthy women. However, additional basic and clinical studies of the relationship between CA-125 and bone are necessary.

Ahn KH, Park HT, Kim T, et al. Relationship between the serum CA-125 level and bone mineral density in healthy pre- and post-menopausal women. Aust N Z J Obstet Gynaecol. 2010;50:371–377.

Correspondence: Young Tae Kim at ytkim1954@hotmail.com