Altruism as an Explanation for Human Consanguinity

BACKGROUND

Human inbreeding is a sociobiological puzzle. Despite widespread knowledge of its potential for genetic disorders, human consanguinity remains surprisingly common. The current reasons explaining its continued persistence in today's modern world have major shortcomings.

SUMMARY

We propose that the Neolithic Agrarian revolution modified the structure of populations. It increased competition for the limited resources in which a larger group had better chances of survival. As a result, small, drifting, socially open bands of hunter-gatherers were transformed into bigger, less mobile, and more powerful kinship groups (tribes). In this transformation, a central role was played by human trust - an aspect of human altruism which is a universal sociobiological principle of behavior. Altruism (and trust) is an essential premise of social contracts such as economic cooperation, marriage arrangement, and creation of alliances between people. In kinship groups, human trust is limited to kin, so tribes remain small, economically poor, and consanguineous due to lack of nonkin mates. The expanding of trust from kin to that of nonbiological relatives increases the size of human groups, fosters economic wealth, and decreases the rate of consanguinity. Key Messages: The lack of nonkin altruism leads to: (a) poverty (due to poor economic cooperation with nonkin), (b) maintaining small group size, and (c) inbreeding.

Consensus Statement by an Expert Panel on the Diagnosis and Management of Iron Deficiency Anemia in the Gulf Cooperation Council Countries

BACKGROUND

Iron deficiency (ID) and ID anemia (IDA) are common in the member states of the Gulf Cooperation Council (GCC). The unique genetic and lifestyle factors of the patient population in the region have necessitated the development of recommendations to help educate health-care professionals on appropriate diagnosis and management of ID/IDA.

METHODS

A panel of regional experts, including gastroenterologists and hematologists with expertise in the treatment of IDA, was convened to develop regional practice recommendations for ID/IDA. After reviewing the regional and international literature, the expert panel developed consensus recommendations for screening, diagnosis, and treatment of patients with IDA in the GCC region.

RESULTS

The recommendations proposed were customized to the patient population keeping in view the increasingly recognized burden of coeliac disease, high fertility and obesity rates, high prevalence of alpha- and beta-thalassemia traits, and poor tolerance and low treatment compliance with oral iron therapy.

CONCLUSIONS

This consensus statement proposes recommendations for screening, diagnosis, and treatment of IDA in the GCC region.

Breast cancer protection by genomic imprinting in close kin families

Human inbreeding generally reduces breast cancer risk (BCR). When the parents are biologically related, their infants have a lower birth weight due to smaller body organs. The undersized breasts, because of fewer mammary stem cells, have a lower likelihood of malignant conversion. Fetal growth is regulated by genomically imprinted genes which are in conflict; they promote growth when derived from the father and suppress growth when derived from the mother. The kinship theory explicates that the intensity of conflict between these genes affects growth and therefore the size of the newborn. In descendants of closely related parents, this gene clash is less resulting in a smaller infant. In this review, we elucidate the different mechanisms by which human inbreeding affects BCR, and why this risk is dissimilar in different inbred populations.

Prevalence of neutropenia in children by nationality

Background

A high prevalence of neutropenia has been reported in several ethnic groups amongst whom many healthy individuals with low neutrophil counts undergo unnecessary investigations. This study aims to ascertain the prevalence of neutropenia (NP) in a large cohort of children from North African, Middle Eastern, and Asian countries residing in the United Arab Emirates.

Methods

Neutrophil counts of 26,542 children (one day to six years of age) from 86 countries were analyzed. The subjects were enrolled in the Well-Child-Care program of Ambulatory Health Services of Emirate of Abu Dhabi, United Arab Emirates. NP was defined as a neutrophil count <1.5 × 10⁹/L and severe NP <0.5 × 10⁹/L.

Results

The neutrophil counts reached a nadir in the fourth week of life and changed slightly from the age of six-months to six-years. The frequency of NP was (from West-to-East): North African Arabs 15.4 %, Green Crescent Arabs 9.8 %, Peninsular Arabs 10.9 %, Iranians 3.1 %, Afghanis 2.5 %, Pakistanis 5.6 %, Indians 10.2 %, and Filipinos 7.3 %. The frequency of severe NP in North African Arabs (Sudanese) was 2.8 %, Green Crescent and Peninsular Arabs ≤1 %, Indians 1.5 %, and Filipinos 1.8 %. In 12,703 Emirati children, the frequency of NP was 10.6 % similar to their adult counterparts.

Conclusion

The prevalence of childhood NP varied considerably by geoethnicity. Measures to prevent the inappropriate investigations of healthy children with benign neutropenia are proposed.

Electronic supplementary material

The online version of this article (doi:10.1186/s12878-016-0054-8) contains supplementary material, which is available to authorized users.

Red cell parameters in infant and children from the Arabian Peninsula

α+-Thalassemia trait and iron deficiency anemia are frequent causes of microcytosis and a common diagnostic challenge in Arabian children. In this study, their prevalences and effects on the red cell parameters were evaluated in 28,457 children aged one day to 6 years. α+-Thalassemia trait was considered to be present when mean cell volume (MCV) was <94 fL at birth and iron deficiency anemia when red cell distribution width (RDW) was >14.5%. The prevalence of α+-thalassemia trait was 15.7% (502/3,191), which was similar to previously reported values for adults (9-14%). Iron deficiency anemia peaked at 7 months (53%) and then declined at a rate of 8% per year. The nadirs of red blood cell count (RBC) and hemoglobin concentration (Hb) occurred at two months of age (physiological anemia). Subsequently, Hb increased at a rate similar to that of MCV, demonstrating the two processes are coupled. The third percentile MCV in children older than 3 months was ≤64 fL, which was significantly lower than that in European children. The third percentile Hb, on the other hand, was similar to that in European children. Thus, α+-thalassemia trait and iron deficiency anemia are exceptionally frequent in Arabian children and their red cell indices are considerably different from European-based norms. Careful interpretation of red cell parameters is required for the evaluation of microcytic anemia in Arabian children.

Half of the Emirati population has abnormal red cell parameters: challenges for standards and screening guidelines

In populations with high prevalences of iron deficiency and thalassemia trait, many apparently healthy individuals have abnormal erythroid parameters, which may cause diagnostic problems in clinical practice. We studied the prevalence and causes of red cell parameter values outside their reference ranges in 394 healthy individuals of Bedouin Arab origin, who had complete blood counts (CBCs), hemoglobin (Hb) analyses and serum ferritin tests done. Their mean age ± standard deviation (SD) was 24.8 ± 4.9 years and 51.8% were females. Overall, 53.0% (209/394) had low Hb, MCV or MCH or high RDW. Anemia was present in 27.0% (55/204) of the women and 3.0% (6/190) of the men. Overall prevalence of MCV < 80.0 fL was 45.0% (176/394) and MCH < 27.0 pg was 48.0% (190/394); RDW > 14.0% was found in 21.0% (43/204) of women and 7.0% (14/190) of men. Of the women, 16.0% had iron deficiency anemia (33/204) and 65.0% had ferritin values of < 30.0 μg/L (133/204). The estimated prevalence of α-thalassemia (α-thal) trait in men was 32.0% (60/190) and that of β-thalassemia (β-thal) trait in both sexes was 3.0% (12/394). In conclusion, half of the healthy Emirati population have abnormal CBC values. For clinical purposes, they require reference standards for red cells that are derived from their own population. Screening of women for iron deficiency is justified due to a high prevalence of iron deficiency.

β-Thalassemia in Abu Dhabi: consanguinity and tribal stratification are major factors explaining the high prevalence of the disease

Tribalism and consanguineous marriages are common in parts of the world with a high prevalence of the β-thalassemia (β-thal) mutations, and increase the risks of homozygosity for this and other recessive disorders. We explored the frequency of β-thal genes and β-thal carriers in 5672 subjects screened before marriage, of whom 2262 were couples. The mean coefficient of inbreeding (F) in the population was estimated from self-reported relationships to prospective spouses in 383 subjects. Overall frequency of β-thal mutations and β-thal carriers in the population were 1.16 and 2.3%, respectively. Among the 14 largest tribes, β-thal carrier frequencies varied from 0 to 13.6%. The estimated F in the population was 0.022. The expected number of couples needed to be screened to detect one couple who were both β-thal carriers in the non inbreeding (F = 0) and inbreeding (F = 0.022) population was 1858 and 646, respectively. However, among 2262 couples, 10 were both β-thal carriers, i.e., 1 in 226 couples, significantly (p = 0.02) more than expected by taking only inbreeding into account. Although β-thal mutations are relatively rare, the burden of β-thal disease is increased eight-fold by tribalism and consanguinity.

Erythrocyte reference values in Emirati people with and without α+ thalassemia

BACKGROUND

Interpreting the erythroid lineage in populations with high frequency of α+ thalassemia allele is challenging due to the high prevalence of α+ thalassemia homozygotes. For such populations, separate reference values for normal and α+ thalassemia homozygotes are needed.

METHODS

We studied the erythroid lineage in 1,079 citizens of United Arab Emirates (UAE). Subjects with abnormal hemoglobin (39), iron deficiency (136) or erroneous entries (8) were excluded. MCV distribution in the remaining individuals (896) was visibly bimodal. Statistical mixture analysis with Normix program was used to separate subpopulations with normal and small red cells. Hardy-Weinberg equation was used to estimate genotype frequencies.

RESULTS

MCV of 78.0 fl separated phenotype-derived normal homozygotes (715) from phenotype-derived α+ thalassemia homozygotes (181). The erythrocyte indices were significantly different between the two groups (p < 0.0001). The overall prevalence of phenotype-derived α+ thalassemia homozygotes (-α/-α) was 0.20 and markedly varied among tribes, 0 to 0.31 (Mean = 0.15). The frequency of phenotype-derived α+ thalassemia allele was 0.44; when accounting for tribal population structure and inbreeding, the calculated frequency was 0.34. These values were very similar to those found in the same population by genotyping and other phenotyping methods. The erythrocyte reference values for phenotype-derived normal homozygotes in Emiratis closely overlapped with those for Caucasians and normal homozygotes defined by genotyping. The reference values for phenotype-derived α+ thalassemia homozygotes in Emiratis also closely overlapped with those for α+ thalassemia homozygotes defined by genotyping.

CONCLUSION

In populations with frequent α+ thalassemia mutations, two sets of erythrocyte reference values could be determined without genotyping.

On some novel aspects of consanguineous marriages

Consanguineous marriages, often viewed as incestuous and objectionable, are more widespread than commonly perceived. They integrate multiple facets of human adaptation: economic, cultural and genetic. The widely touted explanation for the origin and persistence of consanguinity is that it provides many socioeconomic benefits; however, this view may be too simplistic. The bias against consanguinity may preclude an objective understanding of this sociobiological puzzle. Inbreeding increases the speed of selection of beneficial recessive and co-dominant alleles, e.g. those that protect against diseases. In populations endemic with malaria, the prevalence of consanguineous marriages and the frequency of alleles protective against malaria are both very high. Thus, consanguinity could theoretically increase the relative fitness of a population under specific ecological conditions; sometimes, the overall genetic benefits may exceed genetic costs of inbreeding. We discuss some recent evidence from studies on inbreeding along with the reasons responsible for the mating strategy found in some human populations. We contend that a better appreciation of our inherent biases and potential genetic benefits of inbreeding in specific ecological conditions would help us to appreciate the wider picture of consanguinity.

Choice of kin in consanguineous marriages: effects of altruism and ecological factors

BACKGROUND

Despite being associated with multiple genetic problems, consanguineous marriages continue to remain extremely prevalent worldwide. Studying the variation of kin preferences in diverse inbred societies may provide some answers to this paradox.

AIM

To find the reasons for specific kin choice in different geographical areas of the world.

METHOD

We used a set of sociobiological rules (kin altruism, sexuality and inbreeding avoidance) and ecological constraints (e.g. tribal warfare, food availability) that influence human behaviour. The cumulative help that the extended family can provide to a nuclear family was calculated using the coefficient of relatedness between kin in different types of consanguineous families.

RESULTS

The maximum potential support for kin markedly varied between different types of consanguineous marriages. Overall, members of consanguineous families received up to two-and-half times more support than members of non-consanguineous families. In various inbred cultures, preference for a specific type of kin was determined by prevailing ecological limitations and sociobiological factors interacting in a complex manner.

CONCLUSION

In different inbred populations, the ideal kin for a consanguineous marriage is the one who can provide the most altruistic support; however, this choice is influenced by biological rules of behaviour and ecological constraints.

Prevalence, phenotype and inheritance of benign neutropenia in Arabs

Background

Benign neutropenia, i.e., neutropenia not associated with an increased risk of infection, may result in serious medical consequences when a 'standard' definition of neutropenia (absolute neutrophil count (ANC) < 1.5 × 10⁹cells/L) is universally applied to all races. The aims of this study were to determine the prevalence of benign neutropenia among healthy Arabs and evaluate its mode of inheritance.

Methods

ANCs were studied prospectively amongst a healthy indigenous population (n = 1032) from the United Arab Emirates undergoing a nation-wide sickle-cell and thalassemia screening program. The mean neutrophil count and the prevalence of benign neutropenia were compared by age, sex and amongst various tribes.

Results

The mean neutrophil count (× 10⁹cells/L) was 3.3 (range 0.95–7.6). Benign neutropenia was present in 110 (10.7%) subjects of whom 24 (2.3%) individuals had moderate neutropenia (ANC 0.5 – 1.0 × 10⁹ cells/L). In the 22 tribe-family groups, the prevalence of benign neutropenia varied between 0% and 38%. Benign neutropenia showed no difference in the frequency amongst the sexes (p = 0.23) and it was independent of age (Spearman's rho = 0.05, p = 0.13). The age-related mean neutrophil count was the lowest in Arabs when compared with other ethnic groups (Blacks, Europeans and Mexicans). The inheritance of benign neutropenia was consistent with an autosomal dominant pattern; however, the diversity of observed phenotypes suggested the presence of more than one genetic variant for this trait.

Conclusion

Arabs have a high prevalence of benign neutropenia that may be inherited as an autosomal dominant trait.

Consanguineous marriages and endemic malaria: can inbreeding increase population fitness?

Background

The practice of consanguineous marriages is widespread in countries with endemic malaria. In these regions, consanguinity increases the prevalence of α⁺-thalassemia, which is protective against malaria. However, it also causes an excessive mortality amongst the offspring due to an increase in homozygosis of recessive lethal alleles. The aim of this study was to explore the overall effects of inbreeding on the fitness of a population infested with malaria.

Methods

In a stochastic computer model of population growth, the sizes of inbred and outbred populations were compared. The model has been previously validated producing results for inbred populations that have agreed with analytical predictions. Survival likelihoods for different α⁺-thalassemia genotypes were obtained from the odds of severe forms of disease from a field study. Survivals were further estimated for different values of mortality from malaria.

Results

Inbreeding increases the frequency of α⁺-thalassemia allele and the loss of life due to homozygosis of recessive lethal alleles; both are proportional to the coefficient of inbreeding and the frequency of alleles in population. Inbreeding-mediated decrease in mortality from malaria (produced via enhanced α⁺-thalassemia frequency) mitigates inbreeding-related increases in fatality (produced via increased homozygosity of recessive lethals). When the death rate due to malaria is high, the net effect of inbreeding is a reduction in the overall mortality of the population.

Conclusion

Consanguineous marriages may increase the overall fitness of populations with endemic malaria.

Consanguinity affects selection of alpha-thalassemia genotypes and the size of populations under selection pressure from malaria

BACKGROUND

In populations with alpha(+)-thalassemia gene deletion, the practice of consanguineous marriages is common.

AIM

The study explored the impact of consanguinity (inbreeding) on the selection of alpha(+)-thalassemia genotypes in a computer model.

METHOD

In a population under selection pressure from malaria, a single protective mutation (-alpha/alphaalpha genotype) was introduced among normal genotypes (alphaalpha/alphaalpha), and mating allowed to proceed. Heterozygote (-alpha/alphaalpha) and homozygote (-alpha/-alpha) children were 1.5 and 2.5 times more likely to survive malaria than those with normal genotypes. Using different coefficients of inbreeding (F, range 0-0.12), we examined the effect of population size, and the mean number of generations required for the homozygote frequency to reach 0.5.

RESULTS

On average, consanguineous populations were larger than randomly mating populations and the size was directly proportional to F. In more inbred populations,-alpha/-alpha homozygotes reached a frequency of 0.5 faster than in less inbred populations. As the frequency of the alpha(+)-thalassemia allele in a population increases, however, the positive effect of inbreeding on the population growth decreases.

CONCLUSION

Under selection pressure from malaria, consanguinity may increase the speed of selection of-alpha/-alpha homozygotes and provide an advantage regarding population growth over non-consanguineous populations.

Risk of cancer in an inbred population

BACKGROUND

In spite of a high prevalence of consanguineous marriages in Asia and Africa, there has been little epidemiological research on the effect of inbreeding on cancer risk.

METHODS

We conducted a case-control study of 391 native Arabs with cancer and 378 matched healthy controls. All cases had a histologic diagnosis of cancer. Participants were interviewed to collect information on the biological relatedness of their parents. Risk of cancer was determined in relation to the presence of parental consanguinity, coefficient of inbreeding (F), and whether subjects were more (F>or=0.0625) or less (F<0.0625) inbred, and was stratified by sex, age group, and cancer type.

RESULTS

Reduction of overall cancer risk was associated with increased F (P<0.001). In men, F was significantly higher in healthy controls than cancer patients overall (P=0.001) and in both younger (<or=30 years) and older age groups (P=0.003 and 0.013, respectively). In women, reduction of overall cancer risk by increased F was found only in the older age group (P=0.03). Overall, being more inbred was associated with a reduction in overall cancer risk by about 25% (odds ratio (OR), 0.74; 95% confidence interval (CI), 0.64-0.86). For seven of the eight most common cancer types, the risk of cancer was reduced with increased F but these did not reach conventional statistical significance (P>0.05).

CONCLUSIONS

Inbreeding was associated with reduced overall risk of cancer in studied population. Reduction of cancer risk is greater in men than women and, in women, is restricted to those older than 30 years.

Nutritional iron deficiency: an evolutionary perspective

Iron deficiency, with or without iron-deficiency anemia, is so ubiquitous that it affects all populations of the world irrespective of race, culture, or ethnic background. Despite all the latest advances in modern medicine, improved nutrition, and the ready availability of cheap oral iron, there is still no good explanation for the widespread persistence of iron deficiency. It is possible that the iron deficiency phenotype is very prevalent because of many factors other than the commonly cited causes such as a decreased availability or an increased utilization of iron. Several thousand years ago, human culture changed profoundly with the agrarian revolution, when humans turned to agriculture. Their diet became iron deficient and new epidemic infections emerged due to crowding and lifestyle changes. There is convincing evidence that iron deficiency protects against many infectious diseases such as malaria, plague, and tuberculosis as shown by diverse medical, historical, and anthropologic studies. Thus, this change of diet increased the frequency of iron deficiency, and epidemic infections exerted a selection pressure under which the iron deficiency phenotype survived better. Multiple evolutionary factors have contributed in making iron deficiency a successful phenotype. We analyze some of the recent findings of iron metabolism, the theories explaining excessive menstruation in human primates, the unexplained relative paucity of hemochromatosis genes, the former medical practice of "blood-letting," and other relevant historical data to fully understand the phenomenon of iron deficiency. We suggest that, due to a long evolutionary persistence of iron deficiency, efforts at its prevention will take a long time to be effective.

Genetic benefits of consanguinity through selection of genotypes protective against malaria

Consanguineous marriages are usually socially driven and can be genetically harmful. The detrimental effects of inbreeding are the consequence of homozygosity of harmful genes. On the other hand, beneficial effects of inbreeding, theoretically, could be expected in those who are homozygous for protective recessive and codominant genes. Here, we argue that the most common monogenetic conditions in humans, namely, alpha-thalassemia, glucose-6-phosphate dehydrogenase (G6PD) deficiency, hemoglobin C, and Duffy antigen negative red blood cells, which have evolved under pressure from malaria, had their survival and selection enhanced by consanguineous marriages in malaria-infested regions of the world. This hypothesis is supported by several observations. First, the presence of two mutations in homozygotes involving the listed conditions (except G6PD deficiency) imparts better protection against malaria than the presence of one or no mutation (heterozygous or normal genotypes, respectively); consanguinity increases the number of homozygotes, especially at low allele frequency. For G6PD deficiency, inbreeding could increase the allele frequency of the G6PD-deficient allele. Second, there is overlap between, on the one hand, the geographic distributions of malaria, thalassemias, and other red blood cell conditions that protect against malaria and, on the other hand, consanguineous marriages. Third, the distribution of different intensities of malaria infestation is matched with the frequency of human inbreeding. These observations, taken together, offer strong support to the hypothesis that the culture of consanguineous marriages and the genetics of protection against malaria have co-evolved by fostering survival against malaria through better retention of protective genes in the extended family.

Incestuous gene in consanguinophilia and incest: Toward a consilience theory of incest taboo

Westermarck's theory of incest taboo states that inhibition of sexual attraction between biologically close relatives is situational and develops during co-residence in early childhood. By contrast, the biological (genetic) basis of incest taboo is presumed from its universality in all human societies and animals and teleologically, from the need to prevent the detrimental effects of inbreeding. As incest taboo violation is infrequent, the frequency of the presumed gene in the population is believed to be near 100%. We present arguments which suggest that the incestuous gene may exist in all populations and could play an important role in evolution. When malaria emerged 10,000 years ago, human adaptation proceeded by the selection of protective genotypes. Among them, homozygotes for alpha-thalassemia, hemoglobin C, and Duffy antigen negative blood group, have better survival odds in malarious regions than heterozygotes and those with normal genotypes. Since consanguinity increases homozygosity, it increases the number of persons who are resistant to malaria. To pro-create, however, biologically close individuals must not feel sexual aversion that normally develops between those who spend their early childhood together (Westermarck effect). It is reasonable to assume, therefore, that mutation of the gene that discourages inbreeding may have appeared at an early time in evolution, and produced a weak Westermarck effect. This gene (we will call it anti-w) failed to inhibit mating between kins. Inbred offspring of anti-w carriers, would statistically, more likely carry both anti-w and homozygote genotypes which increase fitness in the presence of malaria. Today, alpha-thalassemia is the single most common monogenetic disorders in man with over 500 millions carriers concentrated in malarious regions of the world. The world's consanguineous population is some 500-800 millions and is also concentrated in malarious regions. Population migration has spread the gene outside areas of high malaria endemicity. However, endemicity of malaria provides a worldwide gradient of genotype frequencies which makes the incestuous gene hypothesis testable. We propose that the incestuous anti-w allele was co-selected with some of the genes protective against malaria because anti-w facilitates mating between genetically close individuals whose offspring better survive malaria.

Parental consanguinity and risk of breast cancer: a population-based case-control study

BACKGROUND

An estimated 600 million people in the world have consanguineous parents. The effect of consanguinity on the risk of breast cancer is uncertain. The objective of this case-control study was to examine whether parental consanguinity and different levels of inbreeding affect the risk and pathology characteristics of breast cancer.

MATERIAL/METHODS

Over a 36-month period, consecutive female breast cancer patients were recruited in the main cancer hospital in the United Arab Emirates. All were locally born Arabs with a tissue diagnosis of breast cancer. The controls were locally born Arabs without breast cancer matched to cases by sex, age, and residence. The coefficient of inbreeding (F) of both groups was determined from information they provided about their parents' kinship.

RESULTS

The mean age of the 72 patients and 187 controls was 48.6 years (range: 25-86) and 48.5 years (range: 25-82), respectively (P = 0.46). Consanguinity rates of the patients and controls were 29.2% and 28.9% (P = 0.96) and the coefficients of inbreeding were 0.0117 and 0.0167 (P = 0.21), respectively. More closely inbred women (F > or = 0.0625) were less frequent among patients than controls, but the difference was not statistically significant (P = 0.12). The rates of pathological stage of disease, tumor histologies, and tumor grades were similar between more and less inbred patients.

CONCLUSIONS

Parental consanguinity in Arabs, even when a marriage is between first cousins or double first cousins, was not associated with an altered risk of breast cancer.

Cancer by negative heterosis: breast and ovarian cancer excess in hybrids of inbred ethnic groups

Breast and ovarian cancer rates in Pakistan are significantly higher than in neighboring countries. The cancer rate discrepancies cannot be explained with discrepancies of their risk factors. We propose that observed cancer excess in Pakistan is due to cancer development by negative heterosis. Heterosis occurs when a hybrid has a phenotypic characteristic significantly different from that in either parent (hybrid vigor). At a molecular level, heterosis occurs in a heterozygote when one of the two alleles is inactivated. Gene inactivation occurs by methylation of cytosine in a promoter region of a gene. Initiation of allele inactivation is linked to the factors like stress, gender, diet, or another gene. In heterozygote, inactivation of one of the two tumor-suppressor alleles leads to monoallelic expression. This increases cancer risk in the same way the risk is increased in individual who inherit a single mutated tumor-suppressor gene (hereditary cancer syndrome). In both, cancer by heterosis and inherited cancer syndrome, cancer develops after inactivation of a second allele (second hit hypothesis). In a population, conditions that favor development of cancer by heterosis are those that favor mating of a large number of different homozygotes because they produce a large number of different heterozygotes. Among a large number of heterozygotes, there is an increased chance that some of hybrids will develop cancer by heterosis. In Pakistan, conditions were favorable for cancer development by heterosis because country has a high number of different ethnic groups and brotherhoods all of which have a higher rate of homozygosity due to a high frequency of consanguineous marriages, and marriages between members of different groups occurred because of intense population mixing. Result was birth of a large number of inter-ethnic/brotherhood hybrids (heterozygotes), some of which have developed cancer by heterosis.

Quality of age data in patients from developing countries

BACKGROUND

Age misreporting is common in demographic studies but the prevalence and magnitude of age misreporting in clinical cohorts is unknown. We analysed single-year age distribution and terminal digit preference in cancer patients from developing countries.

METHOD

Age distribution was analysed by plotting a single-year age of 3874 cancer patients from 72 different countries, mainly from the Indian subcontinent and the Middle East, who resided in the UAE at the time of cancer diagnosis. Preference for age ending with digits '0' and '5' was evaluated using Whipple's index (WI), which has value 100 in cohorts without preference. Preference for all 10 terminal digits was expressed as the difference between the found and expected frequencies using Myers blended method and was graphed.

RESULTS

Age data quality was low in cancer patients from the Indian subcontinent (WI = 177) and Middle Eastern countries (WI = 113-204). Females of all nationalities supplied better quality of age data (lower WI) than males. Preference for age ending with digits '0' and '5' was found in all populations except the UAE male citizens who did not show preference for terminal digit '0'.

CONCLUSION

Age data quality in this cohort of patients from developing countries was low. Preference for age ending with numbers '0' and '5' is common. In studies conducted in developing countries, age data quality should be analysed as it may bias results and weaken the power of the study.

Consanguinity as risk factor for cervical carcinoma

Cervical carcinoma is caused by human papillomavirus (HPV). Among the risk factors for HPV infection are having multiple sex partners and sex partners who themselves had multiple sex partners. Women married to relatives are more likely to become infected with HPV and develop cervical carcinoma. Consanguineous spouses have a mild sexual aversion to each other that leads to sex avoidance and increases likelihood of satisfying sexual desire outside the marriage. Sexual aversion develops as a result of spouses growing together in early childhood, which triggers biological imprinting of Westermarck. Westermarck's effect prevents incest in nuclear family. In consanguineous family, it extends to spouses, producing mild sexual antipathy. Because of high prevalence of consanguinity worldwide, it is important to test this hypothesis.

Breast cancer, consanguinity, and lethal tumor genes: simulation of BRCA1/2 prevalence over 40 generations

Marriage between biological relatives is a social custom with a long history in many parts of the world. Today, hundreds of millions of individuals live in consanguineous families. The offspring of consanguineous parents are more likely to have the same two alleles (homozygosity) by descent. In consanguineous family with BRCA1/2 gene mutations, an offspring is more likely to be BRCA1/2 homozygous. The consequences of BRCA1/2 mutation homozygosity in humans are unknown. In knockout mice, BRCA1 or BRCA2 homozygotes die as embryos. Because tumor suppressor genes are conserved and less species-specific than other genes, human BRCA1/2 homozygotes are likely to be biologically non-viable and are unknown to exist. Among the conceptuses of consanguineous couples, there are excess deaths (abortions, stillbirths, perinatal and early-childhood deaths) as well as a decreased risk of breast cancer, especially in younger females. It has been suggested that, in part, the excess deaths are due to BRCA1/2 and other still undiscovered tumor gene homozygotes. To examine the consequences of the long-term practice of consanguineous marriage on the prevalence of lethal cancer genes, we simulated, by computer, the mating of non-consanguineous and consanguineous populations over 40 generations. The program was developed in Basic for a Macintosh computer. The input comprised the rates of consanguineous marriage types and the output parameter was the rate of heterozygotes (carriers) in each generation. The combined prevalence of BRCA1/2 mutation of 1% was used as a starting reference point. Absence of spontaneous mutations and gene flow were assumed. In a randomly mating population, the BRCA1/2 carrier rate decreases on average 0.0035% every 25 years. In a highly consanguineous population, the carrier rate decreases on average 0.022% every 25 years, or six times faster than in a non-consanguineous population. There is a worldwide trend of decreasing breast cancer incidence with an increasing consanguinity rate. In conclusion, the BRCA1/2 and possibly other undiscovered tumor gene carrier rates are significantly lower in consanguineous than in non-consanguineous populations. Gene frequency in a population depends on the rate of inbreeding and length of consanguineous practices. A drift phenomenon may exert a major effect on the carrier rate. Consanguinity may explain part of the worldwide variation of breast cancer incidence.

Consanguinity decreases risk of breast cancer--cervical cancer unaffected

Marriages between third-degree and more distant relatives are common in many parts of the world. Offspring of consanguineous parents have increased morbidity and mortality related to recessive gene disorders. In a population with a high frequency of consanguinity, we examined the frequency of breast cancer (related in part to tumour genes) and cervical cancers (related to virus infection) among offspring of consanguineous and non-consanguineous parents. Study was done prospectively in the United Arab Emirates. Selected were married female citizens, ages 40-65, who attended 12 primary health care clinics for whatever reason. In a face-to-face interview, subjects were asked: (a) about consanguineous marriages in family; (b) if they have or have had breast or cervical cancer; (c) about family history of cancer, cancer screening and other parameters. Tumour diagnosis was confirmed by review of medical records. Of 1750 women invited into study, 1445 (79%) could be used in analysis. Among 579 (40%) women of consanguineous and 866 (60%) of non-consanguineous parents there were 24 and 54 with breast cancer, respectively (RR = 0.66, CI 0.42 - 1.06). In the 40 to 50 age group, breast cancer reported 13 of 446 women of consanguineous and 37 of 633 of non-consanguineous parents (RR = 0.50, Cl 0.27 - 0.93). Cervical cancer had 15 women in consanguineous and 32 in non-consanguineous group (RR = 0.70, Cl 0.38 - 1.28). Number of families with history of breast cancer in consanguineous and non-consanguineous group was 21 and 23, respectively (P = 0.29). The cancer screening rates and other variable values had fairly balanced distribution between the 2 groups. Having consanguineous parents decreases the risk of breast cancer especially in younger women, risk of cervical cancer being unaffected.

Consanguinity and family history of cancer in children with leukemia and lymphomas

BACKGROUND

In native population of the United Arab Emirates (UAE), the rate of consanguineous marriages is 50.5%. This study was designed to determine whether the rates of consanguinity and family history of cancer among the families of children with lymphoid malignancy are different from those in the general population.

METHODS

The study comprised 117 patients from the whole of the country with acute lymphocytic leukemia (ALL) and Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL), ranging in age from 2 to 14 years. The consanguinity rate in the study group was compared with the rate in the general population. To study family history of cancer, the authors matched patients with 117 controls. In a telephone interview, each mother was asked to provide data regarding the biologic relationship between her and her husband as well as that between both sets of grandparents; each was also asked whether any family relative had a cancer and, if so, of what type.

RESULTS

Among the 69 ALL cases, 80% of families were consanguineous and 20% were nonconsanguineous. Among the 26 NHL and 22 HL cases, each group included 3 consanguineous families, 12% and 14%, respectively. The consanguinity rates for ALL, NHL, and HL were all significantly different from the 50.5% consanguinity rate in the UAE population (all three P values < 0.0001). The family history of cancer was more often positive in ALL patients than in controls (odds ratio, 2.14; confidence interval, 1.01--4.53). Overall and for each lymphoid malignancy, there was no difference in family history of cancer between consanguineous and nonconsanguineous groups of cases.

CONCLUSIONS

The consanguinity rate in the families of patients with ALL is significantly higher and in those with NHL and HL significantly lower than that in the UAE population. The family history of cancer is more often positive among ALL cases than controls--consanguinity having no effect.

Knowledge, attitudes, and practices related to breast cancer screening: a survey of Arabic women

BACKGROUND

Incorporating breast cancer screening into day-to-day clinical care leads to early diagnosis and decreases mortality. Patients' participation in screening depends on their knowledge and attitudes, other barriers, and physician behavior.

METHODS

A cross-sectional questionnaire survey was conducted to evaluate knowledge, attitudes, barriers, and practices related to breast cancer screening among Arabic women. A convenience sample was selected from 1,750 women aged 40-65 years who, for any reason, attended primary health care (PHC) clinics in Al-Ain, United Arab Emirates (UAE).

RESULTS

Of the 1,750 invited women, 1,445 agreed to participate; 78 were excluded from analysis because of histories of breast cancer. Breast self-examination (BSE) was practiced by 12.7% of the study population, clinical breast examination (CBE) by 13.8%, and mammography by 10.3%. Knowledge about breast cancer screening was low in the study population. Women were infrequently instructed about or offered screening for breast cancer by health professionals. Being employed was an independent predictor for participation in the three screening examinations.

CONCLUSIONS

Health workers infrequently offered screening examinations and women lacked adequate knowledge about breast cancer screening. Acquired information about barriers to screening may help in the design of effective screening programs for Arabic women.

Longer breast-feeding and protection against childhood leukaemia and lymphomas

The role of breast-feeding in protecting against childhood acute leukaemia and lymphomas is uncertain. We investigated this issue in a case-control study comprising 117 patients, aged 2-14 years, with acute lymphocytic leukaemia (ALL), Hodgkin's (HL) and non-Hodgkin's lymphoma (NHL), as well as 117 controls matched for age, sex and ethnicity. Information was collected via a telephone interview of the mothers. The median duration of breast-feeding among patients was significantly shorter than among controls, 7 (range 0-23) and 10 (range 0-20) months, respectively (P<0.0001). Breast-feeding of 0-6 months' duration, when compared with feeding of longer than 6 months, was associated with increased odds ratios (OR) for ALL (OR=2.47, 95% confidence interval (CI) 1.17-5.25), HL (OR=3.75, 95% CI 0.80-18.69), NHL (OR=4.06, 95% CI 0.82-22.59), and overall (OR=2.79, 95% CI 1.54-5.05). In the patient group, there were a significantly higher number of children and people per family, and patients were of a higher birth order than controls. In multivariate analysis, breast-feeding duration continues to be an independent predictor of lymphoid malignancies (P=0.015). In conclusion, breast-feeding lasting longer than 6 months may protect against childhood acute leukaemia and lymphomas.

Preoperative treatment of advanced skin carcinoma with cisplatin and bleomycin

In advanced skin carcinomas of the head and neck region, the tumor may be unresectable or curative resection or radiation may either fail or produce poor functional and cosmetic results. The goal of this study was to test the ability of preoperative chemotherapy to decrease the extent of needed resection and tumor response. Five patients, three with squamous cell carcinoma and two with basal cell carcinoma, were treated before surgery with three cycles of cisplatin 20 mg/m2 daily for 4 days and bleomycin 20 mg/day for 4 days by continuous infusion every 3 weeks. All patients had advanced cancer in the head and neck region, one had unresectable tumor, two had xeroderma pigmentosum, and one was a 13-year-old child. The history of prior treatments was as follows: radiation therapy (n = 3), systemic chemotherapy (n = 1), surgery (n = 1), and no treatment (n = 1). One patient had complete clinical but not pathologic response, three had partial response, and one had progressive disease. The extent of resection after chemotherapy was dramatically reduced in the patient with a complete response and minimally changed in the patients with partials responses and progressive disease. All patients who underwent surgery became tumor free. Preventable toxicity was symptomatic hypomagnesemia in one patient, reversible elevation of creatinine in one patient, and mild nausea and vomiting in three patients. With this report, the total number of patients with nonmelanoma skin cancer who were treated with cisplatin is 68, and their overall response is 80%. Only 16 reported patients were treated with preoperative chemotherapy, and study of this treatment approach to advanced skin cancer should be pursued.

Frequency and management of germ-cell tumors in a third-world country

Since 1977, advances in the treatment of germ-cell tumors have resulted in a declining mortality from testicular cancer. Simultaneously, a rising incidence of disease was seen in many developed parts of world. However, the frequency of and mortality from testicular cancer have not been reported from any third-world country, where larger and younger populations at risk reside. The age-specific annual incidence of testicular cancer was calculated from information in the cancer registry of Iraq (1986-1988). The data on management of 29 patients with testicular (n=15) and non-testicular (n=14) germ-cell tumors were retrospectively analyzed (9% of all non-seminoma testicular cancers in the country for the 1984-1990 period). The annual incidence of testicular cancer is low in Iraq. Transscrotal biopsy and transscrotal orchiectomy were frequently performed but did not adversely affect patient outcome. A poor outcome was associated with the lack of surveillance after surgery; inappropriate sequencing of chemotherapy, surgery and radiation treatment; and chemotherapy of a low-dose intensity. Tumor marker studies were infrequently done. In conclusion, the annual incidence of testicular carcinoma in this developing country is low, but mortality appears high due to the incomplete penetration of the current medical knowledge into clinical practice.

Three-dimensional survival model of breast cancer patients

The established view point of survival in breast cancer patients is in terms of disease-free survival (DFS). This may be imprecise because a patient with early disease may have three different DFSs: First, from initial diagnosis until local recurrence; Second, from successful treatment of local recurrence until development of metastatic disease; Third, from complete remission of metastatic disease until recurrence of cancer. To include all three DFSs in a single model, we propose a three-dimensional survival surface for breast cancer patients. The survival surface is given as the function of tumor size and number of lymph nodes involved. The survival surface has the cusp geometry that is known to be the only stable structure for a system with two input parameters (tumor size and involved lymph nodes) and one output (DFS). The model casts new light on some views about breast cancer.

Observations supporting the existence of true local metastases of cancer

We propose the hypothesis that around a main invading tumor, there are local metastases in the surrounding tissue/organ. They occur as a result of cancer cell migration through the interstitial matrix and we call them true local metastases. They are composed of individual or nested cells but are difficult to identify because of their nonspecific appearance, close location to the irregular surface of the main tumor and observer's inability to deduce a three dimensional structure from a few two-dimensional histological pictures. The propensity of neoplasms to locally metastasize may vary greatly among different types and stages of tumors. Better knowledge of a tumor's three dimensional spread may influence treatment strategy.

Adult T-cell leukemia/lymphoma in Brooklyn

Fifteen patients with adult T-cell leukemia/lymphoma (ATLL) were identified in less than a two-year period in the Crown Heights-Bedford Stuyvesant section of Brooklyn, NY. All patients were black; nine patients originated from the Caribbean islands and six from the southern United States. Two of the patients were father and daughter, the first evidence of familial occurrence in the United States. Their clinical course was similar to that of previously described patients with this disorder. To our knowledge, these 15 patients represent the largest series of ATLL reported in the United States. We recommend that ATLL be seriously considered in the differential diagnosis of patients with non-Hodgkin's lymphoma, mycosis fungoides, lymphatic leukemia, or hypercalcemia.

The first report of familial adult T-cell leukemia lymphoma in the United States

Two patients, a daughter and her father, developed the acute type of adult T-cell leukemia/lymphoma (ATLL) within a 3-month period. Antibodies against HTLV-I have been found in both wives of the father. The second wife acquired the infection from her husband within 3 years of marriage. The patients described represent the first cases of familial ATLL in the United States. ATLL continues to be frequently misdiagnosed in the United States. A positive family history consistent with this disease in a patient with a lymphoid malignancy may be a helpful clue for earlier diagnosis.