J Community Genet (2012) 3:185–192
DOI 10.1007/s12687-011-0072-y
REVIEW
Consanguineous marriages
Preconception consultation in primary health care settings
Hanan Hamamy
Received: 26 July 2011 / Accepted: 9 November 2011 / Published online: 22 November 2011
# Springer-Verlag 2011
Abstract Consanguinity is a deeply rooted social trend
among one-fifth of the world population mostly residing in
the Middle East, West Asia and North Africa, as well as
among emigrants from these communities now residing in
North America, Europe and Australia. The mounting public
awareness on prevention of congenital and genetic disorders in offspring is driving an increasing number of couples
contemplating marriage and reproduction in highly consanguineous communities to seek counseling on consanguinity.
Primary health care providers are faced with consanguineous couples demanding answers to their questions on the
anticipated health risks to their offspring. Preconception
and premarital counseling on consanguinity should be part
of the training of health care providers particularly in highly
consanguineous populations.
Keywords Consanguinity . Consanguineous marriages .
Preconception counseling . Preconception consultation .
Premarital counseling . Primary health care
Introduction
It is estimated that one billion of the current global
population live in communities with a preference for
consanguineous marriage (Bittles and Black 2010a; Modell
and Darr 2002). Consanguineous marriage is traditional and
respected in most communities of North Africa, Middle
Special Issue: Genetic aspects of preconception consultation in
primary care.
H. Hamamy (*)
Department of Genetic Medicine and Development,
Geneva University Hospital,
Geneva, Switzerland
e-mail:
[email protected]
East and West Asia, where intra-familial unions collectively
account for 20–50+% of all marriages (Bittles 2011;
Hamamy et al. 2011; Tadmouri et al. 2009) [Fig. 1].
Primary health care providers in communities with high
consanguinity rates may be confronted by situations where
they are asked to provide preconception counseling to
consanguineous couples. In such countries and communities
where cousin marriages are customary, many young couples
nowadays present to health care providers seeking a scientifically sound answer to their questions including: “Will our
children be physically or mentally abnormal?” “How can we
minimize the risks for having affected children?”
Reports have indicated that there may be inconsistencies in
counseling for consanguinity among health care providers
(Bennett et al. 1999). It is important that primary health care
providers, specifically in highly consanguineous communities, have clear evidence-based guidelines in counseling a
consanguineous couple to minimize their risks for having
affected offspring. This review aims to portray the definition
and current global trends of consanguinity, and propose
simple guidelines for preconception counseling related to
consanguinity based on published studies of health burden
and social benefits of consanguinity. Such data could guide
health care providers and help consanguineous couples take
informed decisions regarding their reproductive choices.
Definition of consanguinity
In clinical genetics, a consanguineous marriage is defined
as a union between two individuals who are related as
second cousins or closer, with the inbreeding coefficient (F)
equal or higher than 0.0156 (Bittles 2001), where (F)
represents a measure of the proportion of loci at which the
offspring of a consanguineous union is expected to inherit
identical gene copies from both parents. This includes
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J Community Genet (2012) 3:185–192
Fig. 1 Global consanguinity rates
unions termed first cousins, first cousins once removed and
second cousins. In some communities, the highest inbreeding coefficients are reached with unions between double
first cousins practiced among Arabs and uncle–niece
marriages practiced in South India where (F) reaches
0.125 (Hamamy et al. 2011) [Fig. 2].
Fig. 2 Categories of
consanguineous marriages
In highly consanguineous populations, pedigrees with
complex consanguinity loops arising from cousin marriages
in successive generations are encountered leading to higher
inbreeding coefficients. Reports on consanguinity rates may
sometimes include marriages between third cousins or more
distantly related individuals. Although this discrepancy
J Community Genet (2012) 3:185–192
187
affects the total consanguinity rate, the lower coefficients of
inbreeding in more remote unions limit a marked alteration
of the mean inbreeding coefficient (α). To report and
compare consanguinity rates among different populations,
the two parameters best used are the mean inbreeding
coefficient and the rates of marriages between first cousins.
negotiations regarding financial matters of marriage are more
easily conducted and sometimes less costly. Wife’s parents
prefer to have their daughter living near them and to enjoy
the presence of their grandchildren. Moreover, wealthy
landlords may prefer to keep their property within the family
(Bittles 2001; Hamamy and Bittles 2008).
Global consanguinity trends
Consanguinity and health parameters
In populations of North Africa, West Asia and South India,
consanguineous marriages are culturally and socially
favoured and constitute 20–50% of all marriages [Fig. 1],
with first cousins unions accounting for almost one-third of
all marriages (Bittles 2011; Tadmouri et al. 2009). The
prevalence of consanguinity and rates of first cousin marriage
vary widely within and between populations and communities, depending on ethnicity, religion, culture and geography.
Consanguineous marriages are also practised among emigrant
communities from highly consanguineous countries and
regions, such as Pakistan, Turkey, North Africa and Lebanon,
now resident in Europe, North America and Australia
(Hamamy et al. 2011; Schulpen et al. 2006).
The high consanguinity rates, coupled by the large family
size in some communities, could induce the expression of
autosomal recessive diseases, including very rare or new
syndromes which increase the public awareness of the risks
associated with consanguineous marriages. Currently, many
young consanguineous couples planning to have children seek
preconception genetic counseling for fear of the consequences
of consanguinity on their offspring.
Health care providers and genetics specialists could consider
both the negative impact of consanguineous marriage in terms
of increased genetic risks to the offspring, as opposed to the
potential social and economic benefits (Hamamy et al. 2011).
The reproductive health criteria related to consanguinity
show that in first cousin marriages as opposed to nonconsanguineous marriages, fertility rate is slightly higher,
abortion rate is not different, stillbirths and infant mortality
rates are slightly higher and birth defects frequency is
estimated to be around 2–3% points more than the
background rate among newborns in the general population
(around 2–3%). Furthermore, consanguineous unions lead
to increased expression of autosomal recessive disorders
(Bittles et al. 1991; Bittles and Black 2010b; Hamamy et al.
2011; Tadmouri et al. 2009). The offspring of consanguineous unions may be at increased risk for recessive disorders
because of the expression of autosomal recessive gene
mutations inherited from a common ancestor. The closer the
biological relationship between parents, the greater is the
probability that their offspring will inherit identical copies
of one or more detrimental recessive genes. For example,
first cousins are predicted to share 12.5% (1/8) of their
genes. Thus, on average, their progeny will be homozygous
at 6.25% (1/16) of gene loci (Bennett et al. 2002).
In general, consanguinity does not increase the risk for
autosomal dominant conditions in offspring when one of
the parents is affected, nor for X-linked recessive conditions if neither parent is affected (Hamamy et al. 2007b).
Most of the literature studying the association of Down
syndrome with parental consanguinity concluded that no
such association existed. The association of consanguineous
marriages with late onset complex diseases such as diabetes,
cardiovascular disorders, schizophrenia and cancer requires
further studies to precise any existing risks because currently
unambiguous evidence-based conclusions are difficult to
establish (Hamamy et al. 2011).
Why are consanguineous marriages culturally
favoured?
The actual reasons given for the preference of consanguineous marriages are primarily social. In communities with
high consanguinity rates, sociological studies indicate that
consanguineous marriage could enforce the couples’ stability due to higher compatibility between husband and wife
who share the same social relationships after marriage as
before marriage, as well as the compatibility between the
couple and other family members.
Consanguineous marriage may be more favourable for the
women’s status, including the wife’s better relationship with
her in-laws who could support her in time of need. There is a
general belief that marrying within the family reduces the
possibilities of hidden uncertainties in health and financial
issues. It is believed that consanguinity strengthens family ties
and enforces family solidarity, with cousin marriage providing
excellent opportunities for the transmission of cultural values
and cultural continuity (Sandridge et al. 2010). Premarital
Preconception and premarital counseling
for consanguinity
Preconception genetic counseling for consanguinity is
considered one of the important pillars amongst the
188
community genetic services in highly consanguineous
populations. Premarital counseling is another increasingly
demanded service in some countries and communities
where consanguinity rates are still high and selective
abortion of affected fetus is not feasible and/or not
acceptable. Marriage in many such countries is regarded
as a family decision and not just the couple’s decision,
although the frequency of “arranged marriages” may be
declining in recent years due to the increasing number of
females reaching university level education which gives
them a broader choice of marriage partner. Many marriages,
whether both interfamilial and intrafamilial (consanguineous), are however still considered arranged marriages in
some communities. The term “arranged marriage” does not
mean that the marriage is planned against the will or
acceptance of either partner, but it basically implies that a
certain suitable couple is given the option of getting
married under the family supervision. Among marriages
contracted from 1969 to 1979 in Jordan, 73.3% of 1983
marriages were arranged through parents’ agreement first
and then couples’ consent, while in 18.6%, the marriage
was through the couples’ agreement first then the parents’
consent (Khoury and Massad 1992).
In populations with high consanguinity rates and
common inherited blood disorders, community programs
for premarital screening to detect carriers of hemoglobinopathies such as thalassemia and sickle cell anemia are in
progress as for example in Jordan (Hamamy et al. 2007a),
Saudi Arabia (Memish and Saeedi 2011), Iran (Fallah et al.
2009), Iraq (Al-Allawi and Al-Dousky 2010), Bahrain
(Al-Arrayed 2005) and Turkey (Mendilcioglu et al. 2011).
Carrier detection and genetic counseling programs have
been very successful in reducing the birth prevalence of
inherited disorders in some populations, such as in Iran
(Khorasani et al. 2008; Samavat and Modell 2004). These
programs are most successful when they are sensitive to the
cultural backgrounds of populations in which they are
applied. In Saudi society, although premarital screening to
identify carrier status and the provision of appropriate
counseling has tremendous potential to prevent inherited
disease (Meyer 2005), results from a screening program for
sickle cell disease and β-thalassemia indicated that about
90% of couples in Saudi Arabia at risk of having affected
children still decided to marry because of fear of social
stigmatisation and/or because wedding plans could not be
cancelled, which emphasizes the need to conduct premarital
screening well in advance of the wedding. One option to be
explored is the introduction of screening during secondary
school (Alswaidi et al. 2011).
In addition to their primary goals, premarital screening
programs in some communities have helped in raising the
public’s awareness of genetic diseases in general, their
prevention possibilities and the fear that consanguinity is a
J Community Genet (2012) 3:185–192
risk factor for expression of recessive disorders, which has
led to an increase in numbers of couples seeking premarital
and preconception counseling for consanguinity.
In countries such as Tunisia, premarital genetic counseling is obligatory for all couples with a history of genetic
complications and in cases of consanguinity (ChaabouniBouhamed 2008). Premarital counseling is also frequent in
some countries offering population-based genetic counseling. For example, in Shiraz, southern Iran, among 2,686
couples presenting for genetic counseling during a 4-year
period, data files revealed that 85% had consanguineous
relationships (74% were first cousins). Most prevalent
reasons for referral were premarital counseling (80%), with
89% consanguinity. Premarital genetic counseling poses
unique challenges and opportunities in such countries
where the tradition of consanguinity is likely to persist
(Fathzadeh et al. 2008).
Preconception carrier screening for hemoglobinopathies
is debated in the Netherlands, a country with immigrants
from populations known to have high rates of hemoglobinopathies and high consanguinity rates. A study assessing
the intentions to participate in preconception carrier
screening for hemoglobinopathies among Turkish female
immigrants reported that of the 109 women enrolled in the
study, 83.5% would participate in preconception carrier
screening, if it was offered. Although the acceptability of
preconception carrier screening was high, the degree of
acceptability of prenatal testing and termination of affected
pregnancies was relatively low (van Elderen et al. 2010).
Proposed steps in preconception counseling
for a consanguineous couple
In offering preconception counseling for consanguinity, it is
crucial to distinguish between families with a known
genetic or inherited disorder and those with no known such
disorder by taking a detailed family history and constructing a four-generation pedigree (including offspring, siblings, parents, grandparents, aunts, uncles, nieces, nephews
and first cousins of the consultand or proband) (Fig. 3)
(Bennett et al. 2002). Reports have shown that in certain
clinical settings, practice guidelines regarding collecting
information on consanguinity as part of family history are
not available, despite the relevance of such history in
identifying at-risk pregnancies (Bishop et al. 2008).
Specific questions addressed to the couple could help in
eliciting the presence of a genetic or hereditary disorder in
the extended family. These could include inquiry about the
presence of any of the following in blood relatives:
&
&
&
Birth defects or congenital anomalies
Early hearing impairment
Early vision impairment
J Community Genet (2012) 3:185–192
189
Fig. 3 Steps in preconception counseling for a consanguineous couple
&
&
&
&
&
&
Mental retardation or learning disability
Developmental delay or failure to thrive
Inherited blood disorder
Unexplained neonatal or infant death in offspring
Epilepsy
Undiagnosed severe condition
In families with hearing, vision or mental disabilities,
informative family history coupled by clinical data and
investigations could differentiate cases that are associated
with consanguinity from cases caused by other factors.
If there is no known genetic disorder in the family, first
cousin marriages are generally given a risk for birth defects
in the offspring that is double the population risk (Stoltenberg
et al. 1997) (for example, instead of 2.5%, it becomes 5%),
or the risk may be given as 1.7–2.8% higher than the
population background risk, mostly attributable to autosomal
recessive diseases (Bennett et al. 1999, 2002; Tadmouri et al.
2009; Zlotogora and Shalev 2010). Closer consanguineous
relationship such as a double first cousins couple may be
given a higher risk for their offspring which may be
estimated at triple the rate of birth defects in the general
population (Christianson et al. 2006). Couples who are more
distantly related could have a similar risk of birth defects
in their offspring as first cousin couples in highly inbred
populations. This may be due to the fact that in such
inbred populations the actual relationship coefficient
among two individuals is much higher than the one
calculated based on information given by the couple
(Zlotogora 2002). On the other hand, among non-inbred
general population, the risk to offspring of a couple related
more distantly than first cousins could be close to that of a
non-related couple (Stoltenberg et al. 1997). It also appears
that the offspring of first cousin marriages are not at an
increased risk for birth defects in their children if they are
married to a non-relative (Zlotogora 2005).
The higher risk for infant mortality could be mentioned
to the couple, although practically speaking, it is very
difficult for the counselor to give the accurate percentage
because the risk depends on the general population
parameters which are not always known. Multinational
studies among first cousin progeny indicated that there is a
mean of 1.1% excess infant deaths over that of the nonconsanguineous progeny (Bittles and Black 2010b), with an
equivalent excess of 3.5% in pre-reproductive mortality
(Bittles and Black 2010a). Individual studies can give
different risk figures dictated by various factors, including
factors inherent to the studied populations. For example, in
Norway, the risk of stillbirth and infant deaths among first
cousin couples was 1.7 times that for unrelated parents
(Stoltenberg et al. 1999).
If family history points to the presence of a genetic
disorder, then primary health care providers could refer the
couple to a specialized genetic counseling clinic. This helps
in estimating the precise risks to the offspring and in
diagnosing their carrier status for autosomal recessive
disorders known to be present in the family whenever such
tests are feasible and applicable.
190
When a consanguineous couple presents to the genetic
counseling clinic because they know that they have a
genetic disorder in their family, a stepwise procedure is
attempted starting with construction of a pedigree and
taking a detailed family history. Several reports have
emphasized the importance of constructing an extended
family tree (usually three generations) as a tool to discover
genetic diseases in the family (World Health Organization
2010), and in some cases to elicit the modes of inheritance.
If the condition follows an autosomal recessive mode of
inheritance, accurate clinical and molecular diagnosis in the
affected is attempted whenever feasible. If the molecular
diagnosis is reached, the couple can be tested for carrier
status of the condition. Difficulties arise at this step when
the affected cannot be reached, refuses testing or is
deceased, with the consequence of inability to reach an
accurate diagnosis to test the couple for carrier status. In
this case, the couple is given estimates for their risks of
having an affected child based on the pedigree. This
scenario may not suffice the couple who request a direct
advice from the counselor on how to minimise their risks
for having an affected child. According to the principles of
genetic counseling, it is expected that the counselor remains
neutral, a position that may not satisfy the couple. Genetic
counselors, although frequently asked what they themselves
would do if placed in the consultand's position, should
avoid being drawn into expressing an opinion.
If the disorder in the family indicates that it is
following an autosomal dominant mode of inheritance,
the risks to offspring of non-affected parents are very low,
estimated according to the frequency of non-penetrance of
the disorder. When the father is not affected by an Xlinked recessive disorder propagating in the family,
consanguinity does not increase the risk for having a
child with such disorder. If the father is affected by a
condition such as G6PD deficiency which is a common
X-linked disorder in the Middle East, consanguinity
among the couple with probability that the wife is also a
carrier of the same gene increases the risk for having
affected daughters.
Complex disorders such as hypertension, coronary artery
disease, diabetes, schizophrenia, autism and cancer are
aetiologically heterogeneous, with multifactorial inheritance
suspected in most families and cases. High susceptibility
genes could play a significant role in the expression of a
complex disease, and if such genes are rare and transmitted
in an autosomal recessive manner then consanguinity could
be a determinant factor. Among highly consanguineous
populations, little has been published on the effects of
consanguinity on the complex late-onset disorders that
account for most of the public health burden (Bittles and
Black 2010a). However, in some families with multiple
affected members and multiple consanguineous marriages,
J Community Genet (2012) 3:185–192
the condition could be associated with consanguinity if
there is a high susceptibility gene present in the family.
Precise risks are usually difficult to estimate in individual
cases.
In communities where arranged marriages are still
practiced, some families with propagating autosomal
recessive conditions that are not amenable to carrier
detection request counseling on further intermarriages.
The decision on limiting such marriages still faces many
problems, and it usually involves members in the family
who do not welcome admitting that the family has a
“hereditary disorder” for fear of stigmatisation within the
family and within a society with low genetic literacy.
Problems can also arise if the disorder in question shows
genetic heterogeneity, such as hearing impairment and nonspecific mental retardation. In these situations empiric risks
can be used which are sometimes not satisfactory to the
family. New technologies including next generation sequencing could eventually help in diagnosing patients
affected by conditions known to be genetically heterogeneous. Moreover, such technologies could diagnose if both
couple carry the same autosomal recessive gene that causes
a severe disorder (Bell et al. 2011). It is envisaged that such
technology could in the future become feasible and
affordable to screen for carrier status and would markedly
reduce the risks for consanguineous couples to have
offspring affected by serious autosomal recessive disorders.
In populations that are highly endogamous, genetic
counseling and screening could be offered with consideration of the genetic disorders that occur with higher
frequency in that specific population (Bennett et al. 2002).
Genetic screening and counseling programs at different
levels of health care have been initiated in some high-risk
communities. For example, in an isolated Druze village in
Israel, where consanguinity rate is high, couples were
screened for four rare inherited diseases that showed a high
carrier frequencies among residents with identification of
ten at risk couples (Falik-Zaccai et al. 2008). Among the
Persian Jewish community of greater Los Angeles, four
relatively frequent autosomal recessive conditions were
screened for, with identification of ten at risk couples
(Kaback et al. 2010). Similar screening projects can be
programmed whenever an inbred community proves to
have high frequency of specific recessive disorders.
Social and educational barriers in counseling
for consanguinity
In some communities, organizational and social barriers
prevent collecting information about consanguinity in
primary health care settings and in midwifery practice,
restricting identification of at-risk pregnancies (Bishop
et al. 2008).
J Community Genet (2012) 3:185–192
The belief that inherited disorders can only arise through
cousin marriages on the paternal side of the family is also
quite common, and in the minds of many people consanguinity may refer only to paternal blood relationships.
Thus, during counseling, if a couple indicate that they are
not related, it is imperative to specifically inquire about any
shared biological relationships on their mothers' sides of the
families. In similar vein, families may opt to avoid cousin
marriages when the disease is inherited as autosomal
dominant and are bewildered and confused by the subsequent birth of an affected baby (Bittles and Hamamy 2010).
Among British Pakistanis, some patients had assimilated
genetic information in ways that conflict with genetic
theory with potentially serious clinical consequences.
Patients referred to genetics clinics may not easily surrender
their lay or personal theories about the causes of their own
or their child's condition and their understandings of genetic
risk (Shaw and Hurst 2008) including the risks of cousin
marriages.
Education of the public in general and of primary health
personnel in particular is an important pillar in clarifying
the health and social effects of consanguineous marriages.
The balance between the possible biological risks of
consanguinity and the social benefits including the nonstigmatisation of the female partner in a society with
minimal genetic literacy could vary among different
couples and different settings. In rural communities, the
social benefits of consanguineous marriages could outweigh their impact on health and vice versa in urban
communities (Bittles and Black 2010a). A point that draws
much debate is whether clear guidelines can be adopted in
certain situations where counselors are allowed to advice
rather than just give risk estimates.
Conclusion
Consanguinity is a deeply rooted social trend with one
billion people currently living in countries where consanguineous marriages are customary, and among them, one in
every three marriages is between cousins. The rising public
awareness on possible preventive measures for congenital
disorders has led to an augmentation in the number of
couples seeking preconception and premarital counseling
on consanguinity.
Consanguineous marriages are associated with an increased risk for congenital malformations and autosomal
recessive diseases, with some resultant increased postnatal
mortality in the offspring of first cousin couples, but
demographic and socioeconomic confounders need to be
well controlled. No major adverse associations with
reproductive parameters such as miscarriages and fertility
have been documented. Associations with quantitative traits
191
and complex adult-onset diseases are vague and inconsistent, suggesting the importance of implementing future
research in this area.
To standardize genetic services, guidelines for screening
consanguineous couples and their offspring are needed.
Consideration could be given to screening based on
common autosomal recessive conditions in the populations
and communities.
In both high and low income countries, there is a
capacity to provide health education for consanguinity at
individual, family and community levels delivered by
primary health care personnel with preconception and
premarital genetic counseling, and diagnosis. Rather than
discouraging consanguineous marriages in populations with
long-held such tradition, ensuring access to preconception
and premarital counseling services is the logical way to
proceed and more likely both to receive community
acceptance and be successful in maintaining and improving
health (Alwan and Modell 1997; Bittles 2009). Increasing
public literacy on consanguinity could be achieved by
providing proper education and training to primary health
care workers on all health and social issues related to
consanguinity.
Conflict of interest The author declares that she has no conflict of
interest.
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