Deficitul de alfa-1 antitripsină – discuţie pe marginea unui caz cu genotip Pi*SZ

Alpha-1 antitrypsin deficiency is a hereditary di­s­­or­der, characterized by a low serum level or alpha-1 anti­tryp­sin function. The disease affects the lungs, liver, kid­neys (membranoproliferative glo­me­ru­lo­­nephritis) and, rarely, the skin (necrotizing pan­ni­cu­litis) or de­ter­mines recurrent vasculitis or aneurysms⁽¹⁾.

We present the case of a 2-year-old male patient, with­out family or personal medical history, referred to our clinic to investigate a hepatocytolysis syndrome.

The patient had been evaluated in another medical unit, six months before, for decreased appetite. The values of the liver enzymes were high: aspartate aminotransferase (AST)=121 U/l, alanine aminotransferase (ALT) =150 U/l. After four months, the liver enzymes’ values were still high (AST=121 U/l, ALT=148 U/l).

On admittance in our clinic, the patient had a good general condition, the weight and height were normal for his age (weight=13 kg, p55, Z score=0.13 SD; height=87 cm, p47, Z score=-0.07 SD; BMI=17.2 kg/m², p69, Z score=0.49 SD), with no changes in the physical exam of the respiratory and cardiovascular systems, without hepatomegaly or splenomegaly.

The laboratory investigations aimed to identify the etiology of the hepatocytolysis syndrome and to assess the liver function. Two months after the last evaluation of the transaminases, these were still elevated (ALT=134 U/l, AST=110 U/l). We found increased values of the gamma-glutamyl transpeptidase (GGT) [82 U/l (normal ranges=6-19 U/l)] and normal values of the direct and total bilirubin and alkaline phosphatase. The parameters of the liver (coagulation, blood glucose, serum albumin) and renal functions were within normal ranges. The patient also had no changes in the complete blood count and the parameters of the inflammatory syndrome (CRP=0.28 mg/dl).

We excluded some infectious causes of the hepa­to­cyto­lysis syndrome (infection with hepatitis B or C viruses, cytomegalovirus, Ebstein-Barr virus, toxoplasmosis), autoimmune hepatitis (ANA, LKM1 and SLA antibodies were negative), celiac disease (anti-transglutaminase antibodies were negative), hyperlipide­mia (cholesterol and triglycerides were within normal ranges), and Wilson disease (ceruloplasmin=0.211 g/l; normal values=0.200-0.600 g/l). We found low values of the serum alpha-1 antitrypsin (initially 26 mg/dl, then 28 mg/dl; normal values=78-200 mg/dl).

The abdominal ultrasound showed no changes in the structure or echogenicity of the liver or other pathological findings. 

The genetic test for the S and Z alleles was performed. The method used was DNA extraction and PCR-RFLP (polymerase chain reaction – restriction frag­­ment length polymorphism). In this case, the result was positive for both alleles, being a compound hete­ro­zygous genotype (Pi*SZ).

Three months after establishing the diagnosis, the liver enzymes’ level decreased (ALT=93 U/l, AST=83 U/l), but the GGT value was slightly increased (95 U/l). The patient is monitored every six months.

Alpha-1 antitrypsin is a glycoprotein formed by 394 amino acids, which is part of a large family of serum in­hi­bi­tors of the proteases, with a unique structure, called “serpines”⁽¹⁾. Alpha-1 antitrypsin inhibits the ac­tion of pro­teases (Pi-protease inhibitor): elastase, trypsin, chy­mo­trypsin and thrombin^(1,2).

Alpha-1 antitrypsin is produced by the hepatocytes, in a proportion of 80%, and in smaller quantities by ma­cro­phages, monocytes, the bronchoalveolar epi­the­lium, colonocytes, and pancreatic endocrine cells⁽²⁾. The neu­tro­phils release an enzyme called neutrophil elastase, which has a role in the “digestion” of the old or destroyed cells, and of the bacteria, stimulating the forming of the new, healthy cells⁽²⁾. It is released in the circulation, representing 80% of the a1 globulins, and diffuses in the tissues, protecting them from the action of the enzymes produced by the inflammatory cells (for example, the neutrophils)^(1,2). Alpha-1 antitrypsin inhibits the neutrophil elastase, preventing the destruction of the healthy tissues^(1,2).

The gene that encodes alpha-1 antitrypsin is called SERPINA 1 (MIM+107400) and is localized on the long arm of chromosome 14 (14q32)⁽¹⁾. Alpha-1 antitrypsin deficiency has a genetic autosomal co-dominant trans­mis­sion, the affected individuals inheriting a gene of the alpha-1 antitrypsin from each parent⁽¹⁾.

It is estimated that alpha-1 antitrypsin deficiency affects 3 million people worldwide⁽³⁾. The Caucasian population is more frequently affected (97% of the diagnosed children)^(3,4), and of these, 35% are boys⁽⁴⁾.

More than 150 alleles of the alpha-1 antitrypsin (SERPINA 1) were identified. The most frequent muta­tion of the gene SERPINA 1 is Z mutation Glu342Lys (re­pre­senting the lysine substitution with glu­ta­mic acid in position 342 of the alpha-1 antitrypsin molecule). Pi*ZZ names the homozygous Z allele^(1,2), and it is considered the classic genotype⁽⁵⁾. A recent systematic review, conducted by Townsend et al., estimated that 75% of the cases diagnosed in children have this genotype, and 4.5% have Pi*SZ genotype⁽⁴⁾.

As in our patient, there are compound heterozygous individulas with two different mutations of the same gene. The patient has an S mutation (characterized by one substitution of an amino acid – valine instead of glutamic acid, in position 264 in the Pi gene of chro­mo­some 14^(1,2)), and a Z mutation on the other chromosome 14 (Pi*SZ).

Recent studies of genetic prevalence suggest that the number of patients with genotype Pi*SZ could be 10 times higher than that of genotype Pi*ZZ⁽⁶⁾. Almost half of the 1.5 million people with genotype Pi*SZ live in Europe^(6,7).

The underestimation of the number of patients with genotype Pi*SZ could be due to the fact that not all of them develop clinical manifestations, and these cases are rarely reported⁽⁵⁾. The data gathered from 97 countries (including Romania), divided into 10 geo­gra­phic regions, by Serres et al. in 2012, showed that 0.7% of all the patients with a genotype characteristic for alpha-1 antitrypsin deficiency have Pi*SZ genotype⁽⁶⁾.

Liver disease is the result of the accumulation in the hepatocyte of a variant of alpha-1 antitrypsin that is not secreted⁽¹⁾. Only the genotypes associated with the pathological polymerization of alpha-1 antitrypsin within the hepatocytes’ endoplasmatic reticulum (for example, alpha-1 antitrypsin deficiency type Pi*ZZ, Pi*SZ) lead to liver damage^(1,2). The large proteic polymers that are formed overwhelm the endoplasmatic reticulum, cause mitochondrial  dysfunction, and activate many intracellular pathways, including caspase and autophagy. All these changes determine liver cells injury⁽⁸⁾. The fact that not all patients with PI*ZZ genotype develop liver disease led to the assumption that a second defect is necessary, and it is possible that this is found in the pathways that cause the cells’ destruction⁽²⁾.

From the histopathological point of view, the ac­cu­mu­lated alpha-1 antitrypsin looks like inclusions in the he­pa­to­cyte that are periodic acid-Schiff reagent positive (PAS-positive)⁽²⁾.

The pulmonary disease (emphysema, bronchiectasis, chro­nic obstructive pulmonary disease) in alpha-1 anti­tryp­sin deficiency is the result of the imbalance between the neutrophil elastase in the lungs, that des­troys the elastin, and the elastase inhibitor, the alpha-1 antitrypsin, that protects against the proteolytic de­gra­da­tion of the elastin⁽¹⁾.

Alpha-1 antitrypsin deficiency is the most frequent ge­ne­tic liver disease and the second most frequent liver trans­plant indication after biliary atresia⁽⁹⁾. Still, it re­mains frequently undiagnosed in childhood⁽¹⁰⁾.

Children can manifest the disease at any age⁽²⁾. Just like in patients with Pi*ZZ genotype, the severity of the symptoms is variable.

Neither the level of alpha-1 antitrypsin, nor the disease’s phenotype are enough to identify which of these patients have a Pi*SZ genotype or will develop pulmonary and/or liver disease⁽⁵⁾. The disease’s evolution and severity depend on numerous factors, independent of the genetic ones⁽⁵⁾.

Heterozygous individuals with alpha-1 antitrypsin deficiency are, most of them, apparently healthy, without symptoms⁽⁹⁾.

Alpha-1 antitrypsin deficiency is frequently mani­fes­ted in infancy with jaundice⁽¹¹⁾. Cholestasis can lead to malabsorption and failure to thrive, abdominal dis­ten­sion, pruritus, hepatomegaly, splenomegaly, hyper­cho­les­te­rolemia, bleeding (superficial ombilical hemor­rhages, or even intracranial bleeding) and ecchymosis⁽⁹⁾.

The patient can also present with neonatal hepatitis, he­patomegaly, splenomegaly or gastrointestinal hemor­rhage, without jaundice⁽⁹⁾. The evolution after the initial symp­toms is variable and fluctuating. Only a small number of children (less than 1%) develop liver failure in infancy⁽⁴⁾.

Although data regarding liver disease in these pa­tients are limited, studies show a high risk for chronic he­pa­to­pathy and even cirrhosis⁽⁹⁾. In adults, mild or moderate liver fibrosis is noticed both in Pi*ZZ and Pi*SZ patients, but severe fibrosis is rarely found in Pi*SZ patients⁽⁵⁾.

Hadzic et al. retrospectively reviewed the data of 162 children with alpha-1 antitrypsin deficiency, diagnosed over 14 years, 10 of them having Pi*SZ genotype (6%; 8 boys)⁽¹²⁾. In most of the cases found with Pi*SS and Pi*SZ genotype, the diagnosis at presentation was different, which made them conclude that patients with this genotype are rarely referred to pediatric he­pa­to­logy cen­ters. Also, the role played by alpha-1 anti­tryp­sin defi­ciency as comorbidity is not clear⁽¹²⁾. The pre­do­mi­nance of these genotypes in males is also to be taken into consideration. The authors raise the question whether the genetic factors related to the male sex are involved in the clinical manifestations of alpha-1 antitrypsin deficiency⁽¹²⁾.

The results of the studies assessing prognostic factors are contradictory⁽⁴⁾. The persistence of elevated ALT, AST and bilirubin levels, hepatomegaly, early development of splenomegaly, progressive prolongation of the prothrombin time and reduced inhibition of the tripsyne were correlated with a poor prognosis⁽⁹⁾. In some of the published results, the elevated levels of ALT and GGT at presentation were considered risk factors for later liver transplant⁽⁸⁾. The results were not convincing in other studies⁽⁸⁾. Jaundice – either at presentation⁽¹³⁾, or prolonged (more than six months) – in patients with neonatal hepatitis⁽⁸⁾ was considered in some studies as a risk factor. Still, in other studies, infants with prolonged jaundice had a good prognosis⁽⁴⁾.

Some authors suggested the changes found by liver biop­sy as potential prognostic factors in developing the he­pa­to­pathy⁽⁴⁾. Portal fibrosis and paucity of the bilia­ry ducts are frequently described in infants who pro­gress towards cirrhosis⁽¹⁴⁾ and need or will need a liver trans­plant⁽¹³⁾.

There are no reports of hepatocellular carcinoma in children, suggesting that it is very rare in this age group. In adults, the 1.3% incidence is similar to other di­seases, like cirrhosis caused by alcohol or primary bi­li­ary cholangitis⁽⁴⁾.

In patients with alpha-1 antitrypsin deficiency, liver enzymes, total and direct bilirubin, alkaline phos­pha­ta­se and GGT can be elevated⁽¹⁴⁾. Low levels of the liposoluble vitamins (A, D, E, K) and albumin, or coagu­lation disorders can be found⁽¹²⁾.

Deficiency alleles are associated with a lower than 35% of the normal medium level of the serum alpha-1 antitrypsin⁽¹⁾. The S mutation has a smaller impact on the circulating alpha-1 antitrypsin than Z mutation. The S alleles are associated with secretion of up to 60% compared to the normal M variant⁽⁵⁾. By comparison, the Z alleles lead to secreted levels that are 15% of the normal value. This difference is attributed to the lower poly­merization of the S protein than the Z protein; still, the S variant also forms heteropolymers with the Z one⁽⁵⁾. Therefore, most of the Pi*SZ genotype patients have low alpha-1 antitrypsin levels, but higher than those recorded in individuals with the Pi*ZZ genotype⁽⁵⁾.

In patients with Pi*SZ genotype, the alpha-1 anti­tryp­sin level is 25-40% of the normal, depending on per­son to person, as revealed by studies⁽⁵⁾. The patient we pre­sent had at diagnosis a value of approximately 33% of the normal serum level. It is important to remember that alpha-1 antitrypsin is an acute phase reactant. Like CRP, alpha-1 antitrypsin level can be transiently increased in trauma, inflammation or hormonal changes^(1,5). High levels of CRP are thus related to high alpha-1 an­ti­­tryp­sin levels in patients with Pi*SZ^(2,5). It is useful to simultaneously determine the CRP and the alpha-1 anti­trypsin levels in patients with Pi*SZ genotype^(2,5).

The signs of pulmonary diseases develop later in life in patients with Pi*SZ genotype, unlike patients with more severe alpha-1 antitrypsin deficiency (Pi*ZZ, Pi*Znul or Pi*nulnul genotypes). Most likely, as a result of a higher medium level of alpha-1 antitrypsin, they have a slower evolution of lung disease⁽¹⁾. Pulmonary emphyzema is frequently present in cases with Pi*SZ genotype, especially in smokers^(1,2). Compared with the general population, patients with Pi*SZ genotype also have a reduced percentage of the predicted forced expi­ra­tory volume in the first second^(1,5). The main cause of death is lung disease (pneumonia, pulmonary emphy­sema or fibrosis)⁽⁵⁾.

There is no specific treatment for the hepatopathy in alpha-1 antitrypsin deficiency in children. The­r­a­py with ursodeoxycholic acid was reported to reduce trans­­ami­nases and GGT without changing the outcome⁽¹⁴⁾. The chronic liver disease complications must be solved and monitored by specialists in pediatric he­pa­tology (failure to thrive, deficiencies of the liposoluble vitamins, ascites, pruritus and gastrointestinal hemorrhages)⁽¹⁵⁾.

The substitution therapy with alpha-1 antitrypsin is not recommended in liver disease because it is not due to the lack of antiprotease activity, but to the mutant protein⁽¹⁵⁾. In children with severe chronic hepatopathy complications, a liver transplant might be indicated, and the survival rates are 90% after one year and 80% after five years⁽¹⁵⁾.

It is important to consider alpha-1 antitrypsin de­fi­cien­cy in the circumstances that we mentioned before, since the patients might be asymptomatic or have un­spe­cific symptoms, such as the case of the patient we presented.