Brenda B. Suh-Lailam, PhD,1 Melinda Procter,2 Patti Krautscheid, MS, LCGC,2 Jason Haas, DO,3. Shiva Kumar ..... Silverman EK, Miletich JP, Pierce JA, et al.
AJCP / Case Report
Challenging Identification of a Novel PiISF and the Rare PiMmaltonZ ð1-Antitrypsin Deficiency Variants in Two Patients Brenda B. Suh-Lailam, PhD,1 Melinda Procter,2 Patti Krautscheid, MS, LCGC,2 Jason Haas, DO,3 Shiva Kumar, MD,3 Rong Mao, MD,1,2 and David G. Grenache, PhD1,2 From the 1Department of Pathology, University of Utah School of Medicine, Salt Lake City; 2ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, UT; and 3Aurora St. Lukeâs Medical Center, Milwaukee, WI. Key Words: a1-Antitrypsin deficiency; AAT; Genotype; Phenotype; Mmalton Am J Clin Pathol May 2014;141:742-746 DOI: 10.1309/AJCPR7EIQS8PIMLV
ABSTRACT Objectives: α1-Antitrypsin (AAT) deficiency is associated with an increased risk for lung and liver disease. Identification of AAT deficiency as the underlying cause of these diseases is important in correct patient management. Methods: AAT deficiency is commonly diagnosed by demonstrating low concentrations of AAT followed by genotype and/or phenotype testing. However, this algorithm may miss novel AAT phenotypes. Results: We report two cases of AAT deficiency in two patients: a case of the novel phenotype PiISF, misclassified as PiII by phenotyping, and a case of the rare phenotype PiMmaltonZ misclassified as PiM2Z. Conclusions: These cases highlight the importance of understanding the limitations of a commonly used diagnostic algorithm, use of further gene sequencing in applicable cases, and the potential for underdiagnosis of AAT deficiency in patients with chronic obstructive pulmonary disease.
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α1-Antitrypsin (AAT) deficiency is a relatively common autosomal codominant genetic disorder affecting approximately 1 in every 3,000 individuals.1-5 It is estimated that there are more than 60,000 people with severe AAT deficiency in the United States, but fewer than 10,000 have been correctly diagnosed.6 Mutations in the SERPINA1 gene, which codes for AAT, result in normal, deficiency, null, and dysfunctional protein variants. Patients with AAT deficiency have insufficient concentrations of plasma AAT and/or reduced functional activity of the protein. AAT is synthesized by the liver and functions to degrade neutrophil elastase. Lack of adequate amounts of AAT predisposes individuals to the development of early onset emphysema and chronic obstructive pulmonary disease (COPD). Some AAT variants also cause liver disease due to their ability to polymerize in hepatocytes, leading to hepatocellular death. Risks for disease are increased when more than one allele that codes for a deficient AAT variant is inherited. More than 120 AAT variants have been reported.6 Proteinase inhibitor (Pi) M is the most commonly encountered nondeficiency variant, while PiS and PiZ are the most common deficiency variants.5,7,8 Here, we report two cases of AAT phenotype determination that were challenging due to the presence of rare SERPINA1 genotypes. Case 1 is the first reported case of AAT deficiency due to a novel AAT genotype. The patient described in case 2 had AAT deficiency due to the rare PiMmaltonZ phenotype. In both cases, serum concentrations of AAT were compatible with AAT deficiency. However, accurate phenotypes for both patients could not be determined by the commonly used algorithm of AAT quantification followed by targeted mutation genotyping and phenotyping.9-11 These cases support the need for full gene sequencing in some cases © American Society for Clinical Pathology
AJCP / Case Report
where phenotypic and genotypic analyses are discordant. In addition, the importance of considering the possibility of AAT deficiency in patients with COPD is emphasized.
Case Reports Case 1 A 36-year-old man presented with three days of intermittent epigastric pain, nausea, emesis, and anorexia. His medical history was significant for hypertension and Graves disease. He denied alcohol, tobacco, or illicit drug use. Laboratory investigations revealed the following: alkaline phosphatase, 266 U/L (reference interval, 50-136 U/L); aspartate aminotransferase, 329 U/L (reference limit, T; p.Arg247Cys (R223C in the processed protein) produces a PiF phenotype that yields a dysfunctional AAT protein with reduced catalytic activity. However, PiF differs from both PiI and PiS phenotypes in that AAT is expressed at normal concentrations. Since the AAT serum concentration of the patient described in case 1 was decreased and only the I variant bands could clearly be identified by IEF electrophoresis (Figure 1), we hypothesize that the I mutation is on one allele and both the S and F mutations are on the second allele. It is therefore possible that the allele that harbors both the S and F mutations yields an AAT variant that has a similar migration pattern to the I variant. Therefore, if only phenotype analysis is used, this atypical protein product could be mistaken for an I variant. In this case, misclassification of the patient as PiII would likely not change clinical management as such an individual would be predicted to be at risk for AAT deficiency. The patient described in case 2 was determined by gene sequence analysis to have one copy of the Z allele and another copy of the Mmalton allele. Previous descriptions of AAT deficiency due to PiMmaltonZ have shown that this phenotype is © American Society for Clinical Pathology
associated with a high risk of developing emphysema with clinical features presenting as early as age 37 years.18-20 Despite her long history of COPD, AAT deficiency appears to have not been considered until the seventh decade of life. This case reflects the fact that AAT deficiency is often underdiagnosed.3,4,23 The benefit of diagnosing AAT deficiency earlier in life is that treatment with AAT replacement therapy and lifestyle modification can prevent rapid decline in lung function.17,24-27 The misclassification of this patient as having a single deleterious AAT variant (PiM2Z) could lead to a delay in the diagnosis and clinical management of this individual, since the undetectable AAT protein concentration is inconsistent with the reported phenotype (PiM2Z), necessitating further investigation to rule out possible laboratory error. It is therefore important to correctly classify deleterious AAT variants, allowing for the timely initiation of treatment. The Mmalton protein variant is the result of a deletion of the amino acid residue phenylalanine at position 52 (c.227_229delTCT; p.Phe76del, also known as F52del in the processed protein).14,28 This mutation leads to the production of grossly reduced amounts of AAT, giving a possible explanation for the faint M bands visualized by IEF electrophoresis (Figure 2).20,28 A close examination of the IEF electrophoresis gel shows that the migration pattern of the MmaltonZ phenotype differs slightly compared with the M2Z phenotype (Figure 2). It is therefore possible that the presence of the Mmalton variant can be missed by IEF electrophoresis.
Conclusions Although the diagnosis of AAT deficiency by a proposed algorithm of quantification, genotyping, and phenotyping9-11 is effective in identifying common AAT variants, it is important that laboratorians using this process be aware of its limitations. As demonstrated by the cases presented here, measuring AAT concentrations followed by genotypic and phenotypic assays may fail to identify rare and/or novel AAT phenotypes. It is worth noting that in such rare cases, SERPINA1 gene sequencing may be useful in correctly identifying the AAT genotype. Address reprint requests to Dr Grenache: Dept of Pathology, University of Utah School of Medicine, ARUP Laboratories, 500 Chipeta Way, Salt Lake City, UT 84108; david.grenache@path. utah.edu. ââ Acknowledgments: We thank M. C. Elliott-Jeff, Theresa Kunzler, and Carlos Vance for their technical assistance.
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