Online Supplementary Information
Computation of inbreeding coefficient (F)
The inbreeding coefficient (F) of the sample was inferred relying on previously published
data, based on the frequency of consanguineous marriages in the Sardinian population in the
period 1965-1969.13 We considered this period of reference as appropriate since the years of
birth of patients showed a normal distribution with mean=1972 and SD=14.5 years (N=87, pvalue=.969).
In order to make F (and therefore q) estimation as precise as possible, we have taken into
consideration the area of provenance of the patients (up to the parental generation) when they
were born to apparently unrelated parents. This has been possible thanks to the availability of
detailed data on the frequency of consanguineous marriages (for any given degree of
relationship and for any altitudinal zone) reported in previous studies.13,14
Furthermore, the presence of one patient born to 2nd cousins parents (F=1/64= 0.015625) and
of two born to 3rd cousins (F=1/256=0.00390625) was considered in the calculations (table
S3).
F computation has been carried out in three steps:
1. we estimated α (F for the general population) for each of the four areas in which
Sardinia can be divided on the basis of altitude, relying on the frequency of
consanguineous marriages (1st and 2nd cousins) in every area (table S1);
2. we computed a general F estimate for the whole set of patients as a weighted mean
based on the relative frequency of individuals coming from the four different areas
(when they were born to apparently unrelated parents) and of individuals born to
parents with a certain degree of consanguinity (when they were born to related
parents, table S2);
3. since detailed data on the frequency of consanguineous marriages other than those
among 1st and 2nd cousins were not available and the F computed in table S2 would
have constituted a clear underestimate of the inbreeding coefficient in the Sardinian
population, we added to this estimate the contribution to general F given by other kind
of consanguineous marriages (uncle-niece/aunt-nephew, 1st cousins once removed,
and multiple consanguinity marriages, as reported by Moroni et al. 197213) for the
period 1965-1969 (table S3).
Area
Altitude
1st cousins
2nd cousins
α estimate
plains
less than 200 m
0.3
0.44
0.00025625
coastal hills
200-600 m
0.74
1.3
0.00066563
internal hills a
200-600 m
0.69
1.39
0.00064844
mountains
over 600 m
1.26
2.15
0.00112344
Table S1. Frequency (%) of 1st and 2nd cousins marriages in the four different altitudinal
areas which Sardinia can be divided into (original data from Moroni et al. 197213) and
relative α estimates, where α is the average inbreeding coefficient in the general population. α
calculation was based on the formula ∑ pi x Fi, where pi and Fi are the frequency and
characteristic inbreeding coefficient of consanguineous marriages of the ith degree in the
same population.14
a
Hill towns/cities located more than 10 km away from the sea.
Area of provenance/degree of
relative frequency
α/F
F contribution
in the samplec
relationship of the parents
plainsa
0.00025625
87/178
0.000125246
coastal hillsa
0.000665625
28/178
0.000104705
internal hillsa
0.000648438
45/178
0.000163931
mountainsa
0.001123438
15/178
0.0000946717
2nd cousinsb
0.015625
1/178
0.0000877809
3rd cousinsb
0.00390625
2/178
0.0000438904
Total
178/178
0.000620225
Table S2. General F estimate for the set of patients based on the contribution of every
altitudinal area (for patients born to unrelated parents, α coefficient) or, alternatively, of every
degree of relationship between parents (for patients born to consanguineous parents, F
coefficient).
a
Individuals born to unrelated parents, for whom the altitudinal area of provenance was kept
into account to compute the corresponding F contribution
b
Individuals born to related parents, for whom the degree of relationship of the parents was
kept into account to compute the corresponding F contribution
c
Detailed and unambiguous information on the geographical provenance of parents was
available only for 178 individuals
degree of consanguinity
F contribution
of the parents
1st and 2nd cousinsa
0.000620225
uncle-niece/aunt-nephewb
0.0000103764
1st cousins once removedb
0.0000981951
other (multiple consanguinity)b
0.0000485185
Total
0.000777315
Table S3. Final computation of the total inbreeding coefficient for the sample based on the
frequency of individuals born to related/unrelated parents in the sample.
a
F estimate for the sample reported in table S2.
b
original data from Moroni et al. 197213
Mutational spectrum
allele
count
relative frequency (%)
-441_427del
226
66.47
V1146M
29
8.53
2463delC
22
6.47
213-214delAT
7
2.06
A1018V
6
1.76
G1000R
5
1.47
1512-1513insT
5
1.47
H1069Q
3
0.88
R778W
7
2.06
2304-2305insC
5
1.47
2035delC
3
0.88
G1089V
2
0.59
T993M
2
0.59
V890M
2
0.59
G943S
2
0.59
S921N
2
0.59
G869R
2
0.59
R919W
2
0.59
N1270S
2
0.59
L1043P
1
0.29
S921Q
1
0.29
I748F
1
0.29
3852-3875del24
1
0.29
19-20delCA
1
0.29
2122-8T->G
1
0.29
total
340
100a
Table S4. Detailed mutational spectrum of the sample of Sardinian WD patients included in
the study (i.e. with detailed and unambiguous information on the geographical provenance of
parents, N=178). No significant discrepancies with the mutational spectrum of the whole
sample (N=192) was noticed (data not shown).
a
Slight discrepancies of the total sum of relative allelic frequencies from 100 % (due to
rounding of single frequency values) have been ignored