Ismail K Jalili

FRCS, DO, FRCOphth

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16

Marriage Patterns and Consanguinity

    I K Jalili

16.1  Cohort size

16.2  Marriage patterns

    16.3  Consanguinity in the aetiological groups  
    16.4  Temporal pattern of consanguinity  
    16.5  Subtypes of consanguineous marriages  
    16.6  Consanguinity in the various clinical entities  
    16.7  Analysis of marriage patterns and consanguinity  
    16.8  Consanguinity discussion  
References
       
16.1

Cohort Size 

It was possible to ascertain the pattern of parental marriage in 201 sibships. (Table 16.1)
Symbols used in denoting marriage patterns and the subtypes of cousin marriages are found in the endnote.

       
Table 16.1  Cohort of families with documented marriage pattern

 

Patients

Sibships

Pedigrees

West Bank

289

201

175

Gaza Strip

259

142

105

Others

9

8

8

Total

557

351

288

     
16.2

Marriage Patterns and Consanguinity

In the West Bank (WB), consanguineous marriage was found in 80% of the total marriages and included 66% traceable cousin marriage and a much lower figure of 13.4% of untraceable extended family marriages. In the Gaza Strip (Gaza Strip), the corresponding data were 89.5% for the total consanguineous marriages (traceable, 80.4%; and untraceable 9%. (Table 16.2, Figure 16.1)

Table 16.2  Percentages of consanguinity by aetiology and region

 

  West Bank

Gaza Strip

Cousins

Family

Total

Cousins

Family

Total

Hereditary

<16

74

7.9

82

83.6

11.4

95

16+

61

21

82

85.7

4.1

90

Subtotal

68.6

13.5

82

84.5

8.2

92.7

Non-Hereditary

16

47

21

68

66.6

11

77.7

16+

65

9.5

74.5

57

14.2

71.4

Subtotal

56

15

71

60.8

13

74.8

Cons: Consanguinity

 

     
16.3

Consanguinity by Aetiological Cohort

There are differences in the proportion of consanguinity between the hereditary and acquired cases. In the West Bank, the figures are 82% versus 72% and in the Gaza Strip 92% versus 74% respectively. (
       
16.4

Temporal Increase of Consanguinity

The rate of consanguineous marriage over the 60 years leading to the study and ending in 1997, by region, are presented in 3 age cohorts; namely the sibships of children <15, the sibships of young adults between 15-30 years and sibships of patients over 35 years of age. This reveals an increase in the rate of cousin marriage with a corresponding decrease in the rate of marrying from the same locality/village and unrelated marriages. (Table 16.3, Figures 16.1, 16.2)

Table 16.3  Consanguinity in successive generations

Age

Cousins

Family

Total

Same Village

No Relation

Total

West Bank      <15

106

65

19

12

125

77

9

5.6

28

17

162

100

          15-30

68

64

20

19

88

83

9

8.4

10

9.3

107

100

             >30

10

56

3

17

13

72

3

17

2

11

18

100

Gaza Strip        <15

115

85

8

6

123

91

6

4.4

6

4.4

135

100

          15-30

75

80

5

5

80

85

10

11

4

4.3

94

100

             >30

15

68

4

18

19

86

2

9.1

1

4.5

22

100

Both                <15

221

74

27

9

248

84

15

5.1

34

11

297

100

          15-30

143

71

25

12

168

84

19

9.5

14

7

201

100

             >30

25

68

7

19

32

86

3

8.1

2

5.4

37

100

     
Figure 16.1  Temporal trends of consanguinity by region by age cohort
     
Figure 16.2 Temporal trend in consanguinity in acquired condition

 

     
16.5 Subtypes of consanguineous marriage (Social Concepts)
The frequency of the types of first cousin marriages among the Palestinians in the study showed that type A formed 35.4% (n=83 sibships) of all cousin marriages in both regions. This was followed in frequency by type B at 13% (27 sibships) in the West Bank. In the Gaza Strip, type C was the second most common marriage at 10.5% of the total (11 sibships). (Table 16.4, Figure 16.3) Marriages from the paternal side were 42% (99 sibships) and from the mater≠nal side was 20% (47 sibships). (Table 16.4, Figure 16.3)
Table 16.4  Subtypes of cousin marriages to reflect social customs
 

Cousin Marriages

West Bank

Gaza Strip

OPT

 First Cousin (type A)

46

35.4

37

35.2

83

35.2

 Double first cousin

1

0.8

0

0

1

0.4

 First Cousin (type B)

17

13.1

9

8.6

27

11.4

 First Cousin (type C)

5

3.8

11

10.5

12

5.1

 First Cousin (type D)

9

6.9

6

5.7

16

6.8

 First Cousin (either A or C)

3

2.3

1

1.0

4

1.7

 First Cousin (either B or D)

4

3.1

0

0

4

1.7

 First Cousin (type unknown)

9

6.9

8

7.6

18

7.6

 Subtotal first cousin *

94

72.3

72

68.6

165

70

 First Cousin once removed

9

6.9

6

5.7

15

6.4

 Second Cousin

20

15.4

16

15.2

37

15.7

 Second Cousin once removed

3

2.3

4

3.8

8

3.4

 Third Cousin

2

1.5

5

4.8

7

3.0

 Cousin details unknown

2

1.5

2

1.9

4

1.7

 Subtotal

36

27.7

33

31.4

71

30

TOTAL

130

100

105

100

236

100

 Paternal Side Marriages

54

41.5

49

46.7

99

41.9

 Maternal Side Marriages

30

23.1

15

14.3

47

19.9

* Includes 3 and 4 sibships with double first cousins from the West Bank and Gaza Strip.

 

     
Figure 16.3  Graphics presentation of the degree (types) of consanguineous marriages

16.6 Consanguinity in various clinical entities

The highest consanguinity is found in retinal dystrophies, microphthalmos and albinism, making 80% of cases followed by CG (72%). The least are in anterior segment disorders (18.2%) followed by idiopathic nystagmus (28%). (table 16.5)

Table 16.5  Consanguinity in the common clinical conditions

 

Cousins

Total Cons.

Same Location

Not Related

Total

Retina

Cone Degeneration

6

100

6

100

0

0

0

0

6

100

Rod-Monochromatism

16

89

16

89

0

0

2

11

18

100

Cone-rod

21

78

23

85

2

7

2

7

27

100

Leber's Amaurosis

32

68

39

83

6

13

2

4

47

100

Rod-Cones

42

68

52

84

6

10

4

6

62

100

CACR

4

67

4

67

2

33

0

0

6

100

Macular Degeneration

8

89

8

89

1

11

0

0

9

100

Vitreo-retinopathies

5

71

6

86

0

0

1

14

7

100

Albinism

7

88

7

88

1

13

0

0

8

100

Myopia

10

83

10

83

1

8

1

8

12

100

Anterior Segment / Whole Globe

 

Cong. Glaucoma

27

75

32

89

3

8

1

3

36

100

Cong. Cataract

30

65

35

76

4

9

7

15

46

100

Microphthalmos

13

62

17

81

3

14

1

5

21

100

Colobomas

3

60

5

100

0

0

0

0

5

100

Syndromatic

12

55

13

59

3

14

6

27

22

100

Ant. Segment Disorders

3

50

3

50

1

17

2

33

6

100

Idiopathic Nystagmus

1

33

2

67

0

0

1

33

3

100

Non-Hereditary 

Acquired Conditions

18

56

22

69

5

16

5

16

32

100

Optic Nerve conditions

10

59

12

71

1

6

4

24

17

100

Percentages in bold Italic. Cons.: consanguinity.

     
16.7 Analysis of Marriage Patterns and Consanguinity

This study has also highlighted the high prevalence of consanguinity, and in particular first cousin marriage in this community and the higher consanguinity rate among the families of the blind in comparison with the rest of the population, this is in line with findings in other countries and in particular other Arab countries including neighbouring Jordan.(1), (2) This difference is noticeable between sibships of the hereditary and acquired conditions, a disparity wider in the <16 cohort being 74% and 47% respectively. (Table 16.2) This is in line with the evidence that higher consanguinity causes an increase in genetic disorders.(3), (4), (5), (6), (7), (8), (9)  In addition, the higher prenatal and postnatal mortality rates in the genetic series than in the acquired cases (Appendix ref) reflects other reports that show the increase in pre-reproductive mortality with inbreeding and the higher under 5 mortality in first cousin marriage.(10), (11), (12)

This high consanguinity rate is reflected in the high prevalence of recessive conditions seen in the study which parallels the rate of inbreeding in the community. This is found both in communities where cousin marriage is not the custom as well as in those who practise cousin marriages. (13), (14), (15), (16)

Like the rest of the Arab and Muslim world, first cousin marriages are the commonest type of consanguinity in both regions, although it is higher in the Gaza Strip, with Type A (son and daughter of two brothers) being the commonest followed by Type B (son and daughter of two sister). Such information is important in any educational campaign especially in view of the common misconception that maternal cousinsí marriage is not a relative marriage and does not influence the outcome. Regional variations exist in the pattern of cousin marriage between the West Bank and Gaza Strip with a higher percentage of marriages from the paternal side in the Gaza Strip (46.7%) than the West Bank (41.5%). Conversely, marriage from the motherís side of the family was more common in the West Bank (23%) than the Gaza Strip (14.3%).

The study has also shown a temporal increase in consanguinity in the preceding 35 years in both Palestinian regions (Figure 16.2). In the non-hereditary cohorts, however, there is a decline in the consanguinity rate, perhaps in line with a decline in the consanguinity in general population although the sample size is too small to ascertain this.

The possibility that the rate of consanguinity, and consequently the prevalence of recessive conditions, is different between the refugees and original town and village settlers could not be confirmed or otherwise in this survey as there was a lack of clarity in the definition of the status of refugees in the collected data.

It was also noted by the author that the presence of blindness in sibships can stigmatise these families, especially when several members are affected, and lead to their isolation, as was the case with the pedigree with CRDAI. (Figure 16.4) In this pedigree, individuals descended from the mutant person (who has been identified by the members of the pedigree) are avoided by the remaining extended family. These siblings find no alternative other than taking the risk of marrying from within the family instead of marrying from the extended family or the rest of the village. This can be described as double inbreeding or consanguinity fait accompli.(19)

     
Figure 16. 4  Extended pedigree with cone-rod dystrophy and amelogenesis imperfecta (Jalili syndrome) (19)

     
16.8 Discussion

Consanguinity, particularly between close relatives, is known to increase the risk of recessively inherited disease and multifactorial disorders; but the effects of inbreeding on the prevalence and type of AR disease in a community are complex and difficult to quantify.(11) Many different factors are involved, ie the degree of relationship of the parents; the number of generations over which inbreeding has been practised; whether the genetic abnormality alters biological fitness and the mutation rate of the genetic abnormality.(17)

In this study two figures have been highlighted; those of the hereditary conditions and those of the non-genetic conditions. The former reveals a high rate of consanguinity among the sibships in the hereditary conditions category, reaching 80% of marriages in the West Bank and 89.5% in the Gaza Strip. These compare with those of the genetic conditions in the Jordanian study (Tables 16.6), which is 79%. This agrees with the common finding of increased morbidity in association with consanguinity. (refer to Chapter 9) The trend of consanguineous marriage in the hereditary series has shown an increase over the decades climbing from 67.6% in sibships of patients over 30 years, to 74.4% in the under 16 cohort; a trend which is more noticeable in the Gaza Strip rising from 68.2% to 85.2% in the corresponding cohorts. This is attributed to increasing social isolation as a consequence of the ongoing unrest, together with an increase in the isolation of the remaining affected sibships, caused by local knowledge of an existing condition compounding the problem further.

The figures for consanguinity drop in the non-genetic cohorts to 72% in the West Bank and 74% in the Gaza Strip; but this decrease widens in the <16 cohort to 47% in the West Bank, and 66.6% in the Gaza Strip. This suggests a decline in consanguinity in the general population, mainly in the West Bank, whose figures in general resemble those of Jordan ranging between 49.3% and 58%. 

First cousin marriages are well documented as the commonest type of marriages in this highly inbred population and this is reflected in the study where the rate of recessive disorders is the highest recorded among the studies. (Table 16.7) The author believes the degree of accuracy attained in this study is due to the detailed histories taken and pedigree charts drawn up as part of the study, reducing the rate of undetermined cases and enabling more accurate results. In addition there is a predominance of conditions known to be inherited in an AR manner. These potentially large pedigrees provided the opportunity for gene tracking, gene mapping, and the investigation of phenotype variability.

In the Middle East the high proportion of genetic disease due to AR conditions (50-65%) has also been caused by the high levels of consanguineous marriage practised which range from 16-55% of all marriages.(18)

In other countries that are known to practise consanguineous marriage (Sri Lanka and India), the proportion of children with visual loss from AR disease was also high (52%). In Kenya and Uganda, 44% of children with genetic disease had AR disorders, which is partly explained by the relatively high proportion of children with oculocutaneous albinism (15%). In Ecuador, a largely Catholic country, 54% of children with genetic disease had recessively inherited disorders (Chapter 9).  Many of the children in the study came from very large families with several affected siblings there was a history of parental consanguinity, usually between first cousins. (Table 16.6)

     
Tables 16.6  Comparison of marriage patterns in the West Bank and Gaza Strip with other Arab and Muslim communities worldwide.

 

Cousins

Total Family Marriages

Same Locality

Not

Related

Genetic Cases

West Bank

74.2

82.0

6.7

11.2

Gaza Strip

83.6

95.1

4.9

0.0

OPT Total

77.8

87.6

5.9

6.5

Jordan 33

79

79

-

-

Uzbekistan 43

33

33

-

-

Bradford 94

62

62

-

-

Non-Genetic Cases

West Bank

47.4

68.4

10.3

10.5

Gaza Strip

66.7

77.8

11.1

11.1

OPT Total

54.8

71.0

19.4

9.7

Jordan 33

33

33

-

-

Uzbekistan 43

-

-

-

-

     
References

 

(1)

Khoury SA, Massad D. Consanguineous marriage in Jordan. Am J Med Genet 1992; 43: 769-75.

(2)

al-Salem M, Rawashdeh N. Pattern of childhood blindness and partial sight among Jordanians in two generations. J Pediatr Ophthalmol Strabismus 1992; 28: 361-5.

(3) McKuzick VA. In: McKuzick VA (ed.) Human Genetics, Prentice Hall Inc. New York, 1964 pp 36-7.
(4)

Stoll C, Alembik Y, Dott B, Feingold J. Parental consanguinity as a cause of increased incidence of birth defects in a study of 131,760 consecutive birth. Am J Med Genet 1994; 49: 114-7.

(5) Chaleby K, Tuma TA. Cousin marriage and schizophrenia in Saudi Arabia. Br J Psychiatry 1987; 150: 547-9.
(6)

Becker SM, Al Halees Z, Molina C, Paterson RM. Consanguinity and congenital heart disease in Saudi Arabia. Am J Med Genet 2001; 99: 8-13.

(7)

Al-Gazali LI, Sztriha L, Dawodu A, Bakir M, Varghese M, Varady M, Scorer J, Abdulraaq YM, Bener A, Padmanabhan R. Pattern of central nervous system anomalies in a population with a high rate of consanguineous marriages. Clin Genet 1999; 55: 95-102.

(8)

Teebi AS. Autosomal recessive disorders among Arabs: an overview from Kuwait. J Med Genet 1994; 31: 224-33

(9)

Zakzouk S. Consanguinity and hearing impairment in developing countries: a custom to be discouraged. J Laryngol Otol 2002; 116: 811-6.

(10) Pedersen J. The influence of consanguineous marriage on infant and child mortality among Palestinians in the West Bank and Gaza, Jordan, Lebanon and Syria. Community Genet 2002; 5: 178-81.
(11)

Khlat M, Koury M. Inbreeding and disease: demographic, genetic and epidemiologic perspectives. Epidemiol Rev 1991; 13: 28-41. 

(12)

Bener A, Rizk DE, Ezimokhai M, Hassan M, Micallef R, Sawaya M. Consanguinity and the age of menopause in the United Aarab Emirates. Int J Gynaecol Obstet 1998; 60: 155-60. 

(13) Stern C. consanguinity.In: Stern (ed.) Principles of Human Genetics. WH Freeman & Co. San Francisco, USA. 1973, pp 368-501.
(14)

Bear JC, Nemec TF, Kennedy JC, Marshall WH, Power AA, Kolonel VM, Burke GB. Persistent genetic isolation in outport Newfoundland. Am J Med Genet 1987; 27(4): 807-30.

(15) Green JS, Johnson GJ. Hereditary diseases as causes of blindness in Newfoundland: preliminary report. Can J Ophthalmol 1983; 18: 281-4.
(16)

Merin S, Lapithis AG, Horovitz, Michaelson IC. Childhood blindness in Cyprus. Am J Ophthalmol 1972; 74: 538-42.

(17)

Gelehrter TD, Collins FS. In: Gardner JD (ed.) Principals of Medical Genetics. Williams and Wilkins, London 1990.

(18)

Hamamy H, Alwan A. Hereditary disorders in the Eastern Mediterranean region. Bull World Health Organ 1994; 72: 145-54. 

(19)

Jalili IK, Smith NJ. A progressive cone-rod dystrophy and amelogenesis imperfecta: a new syndrome. 1988, J Med Genet 1988; 25:738-740.

 

Ismail K Jalili 2000-2016