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Hyperphenylalaninemia (HPA) is a group of diseases characterized by a persistent elevation of phenylalanine levels in tissues and biological fluids. The most frequent form is phenylalanine hydroxylase deficiency, causing phenylketonuria (PKU). Among 159 Israeli patients (Jews, Muslim and Christian Arabs and Druze) with HPA, in whom at least one of the mutations was characterized, a total of 43 different mutations were detected, including seven novel ones. PKU was very rare among Ashkenazi Jews and relatively frequent among Jews from Yemen, the Caucasian Mountains, Bukhara and Tunisia. The mutations responsible for the high frequency were: exon3del (Yemenite Jews), L48S (Tunisian Jews) and E178G, P281L and L48S (Jews from the Caucasian Mountains and Bukhara). Among the non-Jewish Israeli citizens, the disease was relatively frequent in the Negev and in the Nazareth vicinity, and in many localities a unique mutation was detected, often in a single family. While marked genetic heterogeneity was observed in the Arab and Jewish populations, only one mutation A300S, was frequent in all of the communities. Several of the other frequent mutations were shared by the non-Ashkenazi Jews and Arabs; none were mutual to Ashkenazi Jews and Arabs.
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- Materials and Methods
Hyperphenylalaninemia (HPA) is a group of diseases characterized by a persistent elevation of phenylalanine levels in tissues and biological fluids. The most frequent form is phenylalanine hydroxylase (PAH; E.C. 220.127.116.11) deficiency, causing phenylketonuria (PKU) or non-PKU HPA (McKusick MIM 261600), and corresponding to about 98% of all HPA cases. Almost 500 different mutations have been identified and listed in the PAH mutation database (PAHdb; http://www.mcgill.ca/pahdb). The number of different mutations in a given population is usually high, with a few prevalent mutations and a large number of private mutations. Moreover, there are substantial differences in the mutational spectra among populations.
There have been four publications on PAH mutations in Israel, three of which reported a novel mutation and the fourth, describing a series of 27 unrelated patients with non-PKU HPA (Avigad et al. 1990; Avigad et al. 1991; Kleiman et al. 1992; Weinstein et al. 1993). In this paper, we present a comprehensive molecular analysis concerning the majority of the patients diagnosed among Israeli citizens since the period that newborn screening began in Israel.
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In 4 of the 163 cases, no mutation was characterized (3 Jews, 1 Arab). In the 292 alleles of the other 159 patients, a mutation was characterized, and a total of 43 different mutations were found. Seven of these 43 mutations have not been previously reported (Table 1): H271Q, V230A, L369V and D17Xfs1 in Jewish patients and L197F, T117fsX78 and S436>Pfs in Arab patients. Each of these seven novel mutations was discovered in one or two alleles, with the exception of L197F, a founder mutation, which was characterized in three Bedouin patients (three alleles).
Table 1. PAH mutations found in Arab and Jewish patients (*novel mutation)
|Mutation||Ashkenazi Jews (18)||Non Ashkenazi Jews (78)||Arabs (45)|
|N (30)||%||N (149)||%||N (87)||%|
|L48S|| ||25||16.8||2|| |
|EX3del|| ||12||8.8|| |
|S349P|| ||8||5.4|| |
|P281L|| ||7||4.7||1|| |
|V230A*|| ||6||4.0|| |
|E178G|| ||4|| ||1|| |
|IVS4-5C>G|| ||3|| |
|R408W||2|| ||3|| ||5||5.7|
|H271Q*|| ||2|| |
|P225T|| ||2|| |
|R241H||6||20||2|| ||2|| |
|R243X||1|| ||2|| |
|T380M||1|| ||2|| ||1|| |
|A104D|| ||1|| |
|A259V|| ||1|| |
|D17fsX1*|| ||1|| |
|D415N|| ||1|| |
|F39>Sdel|| ||1|| |
|L369V*|| ||1|| |
|P211>Hfs||1|| ||1|| |
|R252W|| ||1|| |
|R261P|| ||1|| |
|R53H||1|| ||1|| |
|I174V|| ||1|| |
|Y198_E205>Sfs|| ||2|| |
|T117fsX78*|| ||2|| |
|R176X|| ||1|| |
|S436>Pfs *|| ||1|| |
The Jewish Population
Among the 115 Jewish patients, 34 mutations were characterized, and four of them, IVS10-11G>A, L48S, A403V and A300S, represented 47.1% of the alleles. Many of the patients were of mixed ancestry. In only 18 patients, both parents were Ashkenazi Jews, and among the 78 non-Ashkenazi families, 27 had parents originating from the same country. This latter group included Jewish families from the Caucasian Mountains (7), Tunisia (5), Yemen (4), Bukhara (4), Morocco (3) and Iraq (2).
Among the 18 families in which both parents were Ashkenazi Jews, there was a single patient with classical PKU. The most frequent mutations characterized were A403V (23.3%), R241H (20%) and A300S (10%). These three mutations were also present among non-Ashkenazis, but only A300S was also relatively frequent in this community.
In the 27 non-Ashkenazi families in which both parents originated from the same country, there were 17 patients with classical PKU and three with HPA. Between one and four different mutations were characterized in each of the communities. The Yemenite Jews were the only community in which a single mutation was found and the Jews originating from the Caucasian Mountains, the only group with four different mutations. Among the Jews that had originated from Tunisia, L48S was detected in eight out of the ten alleles. This mutation was also relatively frequent among Jews that had come from the Caucasian Mountains and from Bukhara. In these two Jewish communities, in addition to L48S, the mutations, E178G and P281L, were also frequently identified in 19 out of the 24 alleles. The mutations, E178G and P281L, were unique to Jews that had come from the Caucasian Mountains and Bukhara.
In each of the other communities several mutations were characterized; the definite origin of the mutations was not always clear, because of the mixed origin of the parents. Among Jews originating from Morocco, many mutations were discovered, the most frequent being IVS10-11G>A and S349P. Among Jews that had come from Iraq, the most frequent mutations were A300S and IVS10-11G>A. The parental origin of all the patients with the mutation exon3del supports the concept that this mutation has a unique Yemenite origin.
The Muslim Arab Population
Among the 41 patients, there were 29 patients with classical PKU. Four of the 18 mutations characterized among Muslim Arabs, IVS10-11G>A, IVS2+1G>A, IVS4 -5 G>T and F55LfsX6, represented 53.8% of the alleles. Most of the affected patients lived in three areas: the Negev, the Jerusalem vicinity and the area of Nazareth. In each of these three locations, a major mutation was detected, and several others were present at low frequencies. Among the Bedouin of the Negev, 18 alleles were found and five mutations characterized, with the most frequent mutation being IVS10-11G>A. The mutation, L197F, was novel, characterized in three affected individuals, and unique to one of the Bedouin towns. In the vicinity of Jerusalem, among the 22 alleles, five mutations were characterized, the most frequent being IVS4+5G>T. Among Arabs from Nazareth and from six of the 11 villages surrounding the town in a 10 km radius, there were 24 alleles, and seven mutations characterized. In four of these six villages, a single mutation was detected in homozygosity. The mutation, F55LfsX6, was found among Muslim Arabs in a total of 10 alleles in Nazareth and in three of the nearby villages.
The Christian Arab Population
There were three patients with five characterized mutations. Two of the patients were afflicted with classical PKU, one was a homozygote for IVS2+1G>A, and the other was a compound heterozygote for IVS10-11G>A and R261Q. The third patient was affected with HPA and was a compound heterozygote for L48S and T380M.
The Druze Population
A single mutation R241H was observed in homozygosity in one mild PKU patient.
Comparison between the Jewish and Arab Populations
While marked genetic heterogeneity was observed in the Arab (19 mutations) and Jewish populations (34 mutations), there were a few mutations that were frequent in both communities. Among the mutations identified in 3% or more of the alleles of each of the populations, A300S was the only one that was frequent in the three groups, comprising 9.6% of the Ashkenazi alleles, 8.9% of the non-Ashkenazi alleles and 8% of the Arab alleles. While several of the frequent mutations were shared by the non-Ashkenazi Jews and Arabs, none were mutual to Ashkenazi Jews and Arabs. The mutation, IVS10-11G>A, was found in 18.6% of the non-Ashkenazi alleles and in 16.1% of the Arab alleles, and R261Q was found in 4.1% and 5.7% of the alleles in these respective communities. Most of the mutations were either frequent among non-Ashkenazi Jews or among Arabs, with the most frequent among Jews being L48S (17.2%) and EX3del (8.3%) and among Arabs, IVS2+1G>A (10.3%) and F55fsX6 (11.5%).
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A striking difference in the frequency of classical PKU between Ashkenazi and non-Ashkenazi Jews was observed in the present series of observations. This finding substantiates the observation made after the creation of the state of Israel, that PKU is rare among Ashkenazi Jews (Cohen et al. 1978). In this study, it was confirmed that the high frequency of PKU among the Yemenite Jews (1:5,000 live births) is due to a founder mutation, exon3 deletion, and that it is limited to this community (Avigad et al. 1990).
From the data presented here, several conclusions were drawn with respect to the size of the different Jewish communities and the number of patients. With the exception of the Ashkenazi and Yemenite Jews, in most of the Jewish communities, the frequency of PKU was in direct proportion to the population size. Many of the patients diagnosed were from large Jewish communities from Morocco and Iraq. However, in the relatively small Jewish communities from Tunisia, the Caucasian Mountains and Bukhara, living in Israel, a relatively high number of PKU patients were diagnosed.
Among Tunisian Jews in Israel, the reason for the high PKU incidence was the high frequency of L48S, since the other mutations were rare. The mutation, L48S, has been reported in several countries and is particularly frequent in Italy. Without haplotype data, it is not possible to determine whether it is a single mutation present in different populations, a novel recurrent mutation, or if it represents an ancient Jewish mutation that became frequent among Jews from Tunisia because of genetic drift with a founder effect. The high frequency of the L48S mutation among the Jews from the Caucasian Mountains and those from Bukhara may support such a possibility. This situation resembles the observations made in other disorders, relatively frequent among Jews. For instance, one of the mutations responsible for factor XI deficiency was found among both Ashkenazi Jews and Jews from Iraq. Haplotype analysis demonstrated that it represents an ancient mutation present among Jews before their dispersion and that the present distribution among the different Jewish communities is secondary to a genetic drift (Peretz et al. 1997).
PKU appears to be frequent also among the Jews from the Caucasian Mountains and Bukhara. As opposed to its basis in the Yemenite or Tunisian Jews, in the Caucasian Mountains and Bukhara Jews, the reason is the presence of three relatively frequent mutations, L48S, P281L and E178G. Neither P281L, nor E178G, have been found in any other Jewish communities. While P281L has been reported to be relatively frequent in Greece (almost 19% of the alleles), the mutation, E178G, appears to be rare in non-Jewish populations around the world (Lüleyap et al. 2006).
As already mentioned, PKU is rare among Ashkenazis, a community that represents approximately 50% of the Jews in Israel. Almost all of the cases diagnosed in Ashkenazi Jews were either HPA or mild PKU, and the most frequent mutations were A403V and R241H that have been related to these disorders. In the only Ashkenazi case with classical PKU, both parents were Jews from Russia. The patient was a compound heterozygote for an unknown mutation and E280K. This was the only allele with the mutation, E280K, in the present Jewish sample, a mutation that has been associated with classical PKU in European populations. We may infer, therefore, that this allele of non-Ashkenazi origin represents either a recurrent mutation, or that it was introduced by a mixed marriage. While PKU is rare, many monogenic diseases are relatively frequent among Ashkenazi Jews, such as Tay Sachs, Gaucher disease or familial dysautonomia (Zlotogora et al. 2007). Similarly, PKU is rare among Finns, another population in which many rare monogenic diseases have been reported to be frequent, representing the “Finnish disease heritage” (de la Chapelle, 1993). In both populations, the rarity of PKU, a disease that is frequent in many world populations, suggests in each case the existence of genetic drift.
Among the Arab Israeli citizens, many of the patients were from the Jerusalem vicinity that represents the largest Muslim population in Israel. In the other parts of the country, there were several regions where the disease was relatively rare, while it was frequent in the Negev or in the Nazareth area. Among the Arabs, there were many examples of localities in which a unique mutation was found, often in a single family. The mutation may either be a novel mutation that occurred within the community or a mutation that was introduced in the locality. For instance, among the Druze, a close sect with a very high degree of inbreeding, the disease is rare and was found in only one patient that was homozygous for a novel mutation. On the other hand, F55LfsX6 is an example of a mutation that spread in several nearby localities in the area of Nazareth. A similar pattern of distribution was observed for thalassemia and other genetic diseases in the Arab population of Israel, due to the preference for consanguineous marriage and the relative isolation of the population.
It is interesting to note that mutations, which are particularly frequent in both non-Ashkenazi Jews and Arabs, have been reported in the Mediterranean region. The mutation IVS10-11G>A is considered to be a Mediterranean mutation, and R261Q is particularly frequent, in France (17% of the alleles), Turkey (7%) and Italy (9%) (Lüleyap et al. 2006).
A lot of questions concerning the origin and proliferation of mutations described in this article have not necessarily been fully answered. Haplotype analysis and comparison with other populations will probably provide additional data.