Acta Med Scand 1988; 224: 385-90

Prevalence of Hemochromatosis in Finland

MARKUS KARLSSON, EERO IKKALA, ANTTI REUNANEN, HEIKKI TAKKUNEN, ERKKI VUORI and JUDIT MAKINEN From the Second Department of Medicine, University of Helsinki, the Finnish Red Cross, Blood Transfusion Service, the Research Institution for Social Security, Social Insurance Institution, and the Department of Forensic Medicine and Institution of Pathology, University of Helsinki, Helsinki, Finland

ABSTRACT. Karlsson M, Ikkala E, Reunanen A, Takkunen H, Vuori E, Mtikinen J (Second Department of Medicine, University of Helsinki, Finnish Red Cross, Blood Transfusion Service, Research Institution for Social Security, Social Insurance Institution, and Department of Forensic Medicine and Institution of Pathology, University of Helsinki, Helsinki, Finland). Prevalence of hemochromatosis in Finland. Acta Med Scand 1988;

'Ifansfenin saturation was determined in 11 431 men and 10639 women aged 15 or more drawn from different areas in southern and central Finland and attending a multiphasic health screening examination in 1%7-1972. All the 163 men and 66 women with transfemn saturation 270% at the initial examination and still alive at the end of 1983 were invited to a re-examination. Of the invited persons, 76 % attended the re-examination. Ransfenin saturation and serum fenitin were the initial screening methods in the re-examination. All persons with suspected hemochromatosis were clinically examined and a laparoscopy was performed. Four men and four women were found with unequivocal hemochromatosis. Only one of these cases was diagnosed beforehand. According to these data the prevalence of hemochromatosis in Finland is about 501100000. Key words: hemochromatosis, preva- lence, transferrin saturation, ferritin.

224: 385-90.

Hereditary hemochromatosis is an autosomal recessive disease characterized by progres- sive parenchymal iron overload leading eventually to tissue damage. The putative hemo- chromatosis gene is closely linked to the HLA locus on chromosome 6 (1, 2). Recent reports based on pedigree studies (M), autopsy material (7) or screening of population, outpatients or blood donors (8, 9) suggest hemochromatosis to be essentially more common than was previously supposed on the basis of clinical expression (10). In these reports the frequency of the hemochromatosis gene has been estimated to be 5-9 % and the prevalence of homozygotes 0.2-0.5 % in the population. One recent study, however, suggests a lower prevalence (1 1).

Some hereditary disorders are shown to be extraordinarily prevalent in Finland (12). No data, however, are available about the prevalence of hemochromatosis in our country. Transferrin saturation was included in a large Finnish health screening examination and the study population could thus be used for a further study of the prevalence of hemochro- matosis in the country.

POPULATION AND STUDY DESIGN The Social Insurance Institution's Mobile Clinic Unit camed out multiphasic health screening examinations in various parts of Finland. Total populations, or samples of populations, aged 15 or over, were invited to the study in rural, semi-urban and industrial communities in different parts of the country. Altogether 11 431 men and 10639 women, who would be aged 26-69 years at the end of 1983 (83% of those invited) participated between 1967 and 1972 in southern, south-western, western.

Abbreviation: TIBC = total iron-binding capacity.

25-888714

Acta Med Scand 1988; 224 386 M. Karlsson et al.

central and eastern Finland. Large cities were not included. The majority of participants (75%) from industrial communities were men. Serum iron and total iron-binding capacity (TIBC) were included as laboratory parameters in the multiphasic screening. A detailed description of the population, methods used, and the prevalence of anemia and iron deficiency has been presented in an earlier study (13). The prevalence study of hemochromatosis was started in 1983, over 10 years after the primary health screening examination. The basic study population comprised all those alive at the end of 1983, aged 26-69 years, and with serum iron and TIBC analyzed at the screening examination over 10 years earlier (Table I). By these criteria the study population comprised 10544 men and 10367 women. All those with a transfenin saturation of 70% or over at the primary health screening were invited to give a blood sample for determination of serum iron, TIBC and serum femtin. If at this re-examination transfenin saturation proved to be 370%, or serum femtin exceeded 299 pg , the person was invited to give another blood sample. If transfemn saturation or serum femtin repeatedly appeared to be in the abnormal range, the person was invited into the hospital ward for further investigations, which included laparoscopy, always preceded by the informed consent of the person. Liver biopsies for histology and quantitative iron determination were taken during the laparoscopy .

LABORATORY METHODS Serum iron and TIBC were analyzed according to modifications of standard techniques (14) and serum fenitin by a radioimmunometric assay (15). Liver biopsy sections were stained with hematoxy- lin and eosin, trichrome stain or Giemsa and Perl's Prussian blue stain for iron. Stainable iron in hepatocytes was graded 0 4 (16). Sections were assessed for fibrosis, inflammation and fatty change.

For measurements of hepatic iron concentration, liver samples were put into 3 ml volumetric flasks, dried at 100°C for 5 hours to constant weight (13.1-19.5 mg), and wet-ashed with 0.5 ml concentrated nitric acid (Suprapup) on a hot plate for 5 hours. After that 50-100 pl of 30% hydrogen peroxide was added, if needed to complete digestion. The sample was diluted to the volume of 3 ml with deionized water and the iron concentration w a s measured by a Perkin-Elmer Model 300 atomic absorption spectrophotometer against standards acidified with HN03. Duplicate samples of bovine liver (5.k23.3 mg of NBS Bovine Liver, Standard Reference Material No. 1577) were used as controls. The mean iron concentration ( f 2 SD) for bovine liver between series was 270f41.7 pg/g dry weight (certified value 270f20 pglg for 250 mg aliquots). Average hepatic iron concentration among 86 accidentally died Finnish controls was 638 pg/g dry weight (range 110-1 960) (E. Vuori, unpublished data).

CRITERIA FOR HEMOCHROMATOSIS Hepatic iron concentration of 2500 pg/g dry weight or more with transfenin saturation 370% or serum femtin 2300 pgA was considered diagnostic for iron overload and hemochromatosis in the absence of iron-loading anemia, multiple transfusions or prolonged use of iron medication.

Table I. The number of men and women comprising rhe study population and those participating at different phases of screening

Males Females

Participants at the initial examination Alive at December 31, 1983 Transfemn saturation 370 % at the initial examination

A first repeat blood sample Transfemn saturation 370 % or fenitin 3300 pgll

A second blood sample Screening criteria confirmed Laparoscopy Hemoc hromatosis

1 1 431 10 544

163 1 I8

34 26

8 7 4

10 639 10 367

66 57

Acta Med Scand 1988; 224 Prevalence of hemochromatosis 387

RESULTS

At the initial Mobile Clinic screening 1.5% of the men and 0.6% of the women had a transfemn saturation 270% (Table I). There were no essential geographical differences in the distribution of high transfenin saturation. Of those invited to give a repeat blood sample, 118 of the 163 men (72%) and 57 of the 66 women (86%) participated (Table I). In 34 men (29%) and eight women (14%) transfenin saturation was 70% or over or serum femtin exceeded 299 pgh. Of these, eight men with a median serum femtin of 425 pg/l (range 330-900) did not give another blood sample. Three of them had transfenin satura- tion 270%. The median serum fenitin was 500 pg/l (range 744800) in the 26 men who gave a second blood sample, and 11 of them had a transfemn saturation 270 %. The eight women who all gave a second blood sample had a median serum fenitin of 473 pgh (range 11 1-2 1501, and the transferrin saturation was 70% or over in five of them.

The second blood sample showed that only eight of the 26 men and four of the eight women still had abnormal values according to the criteria used (Table I). They were all invited into the hospital ward. Laparoscopy could be performed on all of them except one man (with serum femtin of 880 pg/l and transferrin saturation of 24%), who refused. Of these subjects, four men and four women satisfied the criteria of hemochromatosis. Table I1 shows their clinical and laboratory details. Hepatic iron concentration of the remaining three laparoscopied men varied between 1500 and I953 pglg dry weight. They had no clinical signs of hemochromatosis but they did show evidence of liver disease (caused by alcohol or probably solvent exposure or advanced fatty infiltration), which could explain their hyperfemnemia.

Arthropathy (arthralgia and arthrosis or arthritis) was the most common complaint among the eight hemochromatosis subjects. Two were diabetics of adult type, two had arrhythmia and four had hyperpigmentation, which was slight in all but subject 3, who was the only one with hepatomegaly and clinically overt disease. Two of the subjects had taken small amounts of oral iron medication, no one had used alcohol in excess. Four persons were on medication for hypertonia. Subject 5 had undefined collagen disease with arthritis

Table 11. Clinical and laboratory details of hemochromatosis probands

l'tansfemn Serum Liver biopsy Liver iron Subject Age" Clinical saturation ferritin dry weight MBId no. Sex (yr) signs* (%) (~g i l ) Iron grade Histology'' (pdg) (P)

F 41 P, A 60 M 47 A 39 M 67 H, P, D, A, G 84 F 52 P, A, D 78 M 57 C, A 80 M 35 A 45 F 58 45 F 46 P, C, A 76

Normal range

300 3 878 3

2800 4 1487 3

392 2 414 3 385 3

1551 4

M 15-230,O-I F 10-150

Fi Fa N Fa N N Fi Fi

3 200 3.2 2 980 5.0

21 950 2.9' 9 380 6.4 3 403 - 4 760 2.0 7 200 1.8

21 200 10.6

(110-1 960)

" Age at time of diagnosis.

hypogonadism. ' N = normal, Fi = fibrosis, Ci = cirrhosis, Fa = fatty infiltration.

' Patient died of pneumonia 7 months after diagnosis when still hyperferrinemic.

H = hepatomegaly, P = pigmentation, D = diabetes mellitus, C = cardiomyopathy, A = arthropathy, G =

Mobilized body iron (MBI) stores estimated by quantitative phlebotomy.

388 M. Karlsson et al. Acta Med Scand 1988; 224

and small vessel arteritis. Hemochromatosis probands were not related with each other and dispersed evenly in the districts screened. All except subject 5 were treated with venesections until hypoferrinemic and the mobilized body iron stores were estimated (Table 11).

DISCUSSION

The study population was not strictly representative of the whole population of the same age in the country, but the distribution of age, occupation and social classes was remark- ably similar to that of the whole country. The study population was drawn from altogether 17 cohorts from different areas of central and southern Finland. Based on these facts it can be assumed that the representativeness approached a reasonable level.

The prevalence study was started a rather long time after the initial health screening. A selective mortality could thus be an important confounding factor. The mortality of the population initially attending the health screening examinations, however, has been con- tinuously followed. In the follow-up of the population initially screened and comprising the basic population of this study, not a single case could be found with hemochromatosis as a primary or contributory cause of death. Moreover, the mortality rate of persons with and without high transferrin saturation appeared to be very similar during the follow-up and there were no appreciable differences in the causes of death in these groups.

Since the beginning of the 1970s a national hospital discharge register has been linked with our study register. One case of hemochromatosis belonging to our study population could be identified with a discharge diagnosis of hemochromatosis. This case, however, w a s also identified by the repeat blood sample screening of our study. These additional data indicate that a selective mortality or non-participation of manifest cases of hemochro- matosis does not affect the results. In the group of non-participants there may certainly be some cases with unknown hemochromatosis. There is no reason, however, to assume that the prevalence would be higher than in those who participated in our study and gave a repeat blood sample. Taking these assumptions into account, the number of prevalence cases would increase by two in men and by one in women, if all those with high transfemn saturation had given a new blood sample. The prevalence of hemochromatosis would thus be 50/100000 in our country.

The primary screening phase in our study depended on high transfemn saturation only. According to experience from other studies (17-19) the use of a similar method has shown to be a reasonably good screening instrument. The most frequent problem has been the relatively large number of false positive cases. In our study, however, they could be sorted out fairly accurately. More problematic is the number of false negatives, which could not be controlled in our study. According to our re-examination some of the hemochromatosis cases once or twice showed a lower transfenin saturation than 70%, while the serum femtin exceeded the screening limit. It can, however, be assumed that the number of these false negative cases most likely was small at the initial examination, considering the results of screening among family members of hemochromatosis probands reported by others (19).

Serum femtin was used in combination with transfemn saturation in the re-examination phase of our study. The combination of these two methods is very efficient in identifying the hemochromatosis cases (18, 19). However, as in other studies (9, 11, 20) these tests in combination also give a fairly large number of false positives, although the number of false negatives is extremely small. Most of the false positive men in our study consumed considerable amounts of alcohol (40-60 g/day) or showed some findings related to heavy alcohol consumption. One of the four false positive women had severe heart failure. These

Acta Med Scand 1988; 224 Prevalence of hemochromatosis 389

cases illustrate that different causes of liver injury may raise the transferrin saturation or serum ferritin.

Serum fenitin correlates well with hepatic iron concentration among hemochromatosis patients (21). The serum femtin level usually exceeds 700 pgA in cases of clinical disease (10, 19). The screening limit for serum ferritin used in our study is rather high for women but even higher values are recommended for men (18). In a recent study serum fenitin of homozygotes of hemochromatosis, with a few exceptions, exceeded the level used in our study (9).

Raised hepatic iron concentration has shown to be the most precise method for detect- ing iron overload (21). The liver iron concentration used by us and some others (22) as the criteria of moderate iron overload (2500 pg/g dry weight) is somewhat lower than the lowest values reported in adult homozygotes of hemochromatosis (about 3 500 pg/g dry weight) (2, 16, 21). Adult patients with clinically manifest hemochromatosis, including those with precirrhotic liver injury, usually have hepatic iron concentration in excess of loo00 pg/g (i.e. 1 %) of dry liver weight (20). According to recent studies, approximately 25% of heterozygotes of hemochromatosis (2) and 10% of patients with alcoholic liver disease (20) have hepatic iron concentrations over 2 500 pg/g dry weight.

As to our results the minimum prevalence estimate of hemochromatosis in the Finnish adult population is 50/100000 and the corresponding gene frequency 2.2 %. Although most of the cases are undiagnosed, as in our study, the disease is still quite rare. This suggestion is supported by the finding that in the whole country only nine deceased persons were reported to have hemochromatosis as the main cause of death between 1969 and 1985 (data from the Central Statistical Ofice of Finland). The prevalence rate estimate in our study is not very far from the rate (100/100000) obtained from southern Sweden (11). The much higher prevalence rates (240-500/100000) also reported (8, 9) could have resulted from selection of study populations or clustering of the disease and use of more liberal criteria for hemochromatosis, and cannot be considered applicable to the Finnish population.

Considering the costs and benefits of this study, further population screening for hemochromatosis seems unrewarding. All available methods, however, should be used to diagnose hemochromatosis in subjects with suspicious symptoms or laboratory findings and in the relatives of hemochromatosis patients.

ACKNOWLEDGEMENT This study was supported by a grant from Oy Hoechst Fennica Ab.

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Received December 28, 1987. Accepted April 6, 1988.

Correspondence: Markus Karlsson, MD, Second Department of Medicine, University of Helsinki, SF-00290 Helsinki, Finland.