408

Table 2. Age at diagnosis for AF508 homozygotes and other CF patients

AF508 homozygotes Others a

< 1month 8 2 1- 2months 2 0 2-12months 4 4 1- 5 years 9 2 6-10 years 0 4

11-15 years 0 2 16-20 years 0 3

Total 23 17

a Fourteen patients had one AF508 allele, three had two unknown mutations

In agreement with the report by Kerem et al. (1989b), AF508 was found almost exclusively against the back- ground of the [XV2c] 1, [KM19] 2 haplotype. The same haplotype was also present on about half of the phase- known chromosomes carrying mutations other than AF508 (14/30, Table 1). A 1 2 haplotype frequency of 87% was calculated for the present sample of Dutch CF chromo- somes (data not shown).

A parameter that may serve as an indicator for the overall clinical severity is the age at diagnosis. So far, we have been able to obtain reliable information on the age at diagnosis of 40 patients. All but 3 of these patients were diagnosed in one clinical center, the Sophia Chil- dren's Hospital, Rotterdam. Twenty three patients were homozygous for the AF508 mutation. Fourteen cases had been diagnosed as CF patients during the first year of life and 10 of these diagnoses were made within 2 months after birth but not through neonatal screening (Table 2). No patient from this group had been diag- nosed after the age of 4. The other category consisted of 14 compound heterozygotes with one AF508 allele and 3 patients with two unknown alleles. More than 50% of the patients from the latter category had been identified after 6 years of age (Table 2). We examined whether there is a significant difference in the distributions of the ages at diagnosis between the AF508 homozygotes and the other patients using Wilcoxon's rank sum test. This showed a significant difference (T = 3.03, P < 0.001). We are currently supplementing the data on the age of diagnosis with specific clinical and physiological features.

Mutat ion analysis at the cystic fibrosis locus in the British popula t ion

Ann Harris, Frances Beards, and Christopher Mathew

Paediatric Research Unit, Division of Medical and Molecular Genetics, United Medical and Dental Schools of Guy's and St. Thomas's Hospitals, 8th Floor Guy's Hospital Tower, London Bridge, London SE1 9RT, UK

Summary. The cystic fibrosis (CF) population of South East England seems to reflect a similar distribution in frequency of the AF508 mutation and its haplotype as- sociation as has been observed in the North American population.

Introduction and methods

The British Caucasian population resident in South East England has undergone extensive genetic analysis at the cystic fibrosis (CF) locus (Harris et al. 1988; Harris 1990). Following the isolation of the CF gene and defini- tion of the major disease-causing mutation (Rommens et al. 1989; Riordan et al. 1989; Kerem et al. 1989b), this population in South East England has been analysed fur- ther.

The methods used for D N A analysis are described in the Summary Table at the end of the study.

Results and discussion

Information on the presence or absence of the AF508 mutation in each CF gene has been correlated with the haplotypes for the closely linked D N A markers XV2c and KM19 on the same chromosome. It has been known for some time that these two markers are in strong linkage disequilibrium with the CF locus (Estivill et al. 1987a, b). In our population, 86% of CF chromosomes carry the B haplotype that has allele 1 for XV2c in combination with allele 2 for KM19 (Table 1). Of these B haplotype chromosomes, 82% (102/124) carry the AF508 deletion

Acknowledgements. We thank the patients and their relatives who made their DNA available for analysis. We gratefully acknowledge the help and support of Professor H. Neijens, Dr. M. Sinaasappel (Sophia Children's Hospital), Dr. B.A. Oostra (Department of Cell Biology and Genetics), Dr. F. J. Los and Professor H. Galjaard (Department of Clinical Genetics). This work was supported in part by the Dutch Liver Gut Foundation (H.J.V.).

Table 1. Haplotypes for XV2c and KM19 in CF carriers

Haplotype XV2c/KM19 CF Non-CF Total (%) (%)

A 1 1 5 55 60 (3.4) (37.9)

B 1 2 126 24 150 (86.3) (16.6)

C 2 1 9 49 58 (6.2) (33.8)

D 2 2 6 17 23 (4.1) (11.7)

146 145 291

Table 2. Haplotype correlations with AF508 status on CF chromo- somes

Haplotype XV2c/KM19 AF508 status

+ AF508 - AF508

Total

A 11 0 5 5 B 1 2 102 22 124 C 21 0 9 9 D 2 2 1 5 6

Total 103 41 144 (71.5%) (28.5%)

and 18% (22/124) do not (Table 2). The method used to test for AF508 will not distinguish between this mutation and other possible 3 base pair deletions within a 50 base pair region flanking the AF508 site. However , the latter are likely to be rare in comparison with AF508.

In our population 71.5% of CF chromosomes carry the AF508 mutation. Of the 28.5% of CF chromosomes that do not, 54% (22/41) carry the high risk haplotype B for XV2c and KM19. Of the remaining CF chromo- somes without AF508, 12% (5/41) each have haplotypes A and D, and 22% have haplotype C (see Table 2). Only one out of 103 CF genes with the AF508 mutation occurs on a chromosome with a haplotype other than B (in this case haplotype D).

Among the CF patient sample of 75 individuals (in- cluding 2 sets of first cousins), 23 CF patients are hetero- zygous for the AF508 mutation and 9 carry a different mutation in both their CF genes. This patient group in- cludes members of several different ethnic minorities who may carry the CF mutation on a different haplotype and/or have a predominant CF mutation that is different from AF508.

Acknowledgements. The authors thank Professor Martin Bobrow for support, Professor R.W. Williamson for the XV2c and KM19 probes and Carolyn Quinlan for excellent technical assistance. Part of this work was funded by grants from the Cystic Fibrosis Re- search Trust, the Halley Stewart Trust and the Spastics Society.

409

Frequency of the F508 deletion in the CFTR gene in Turkish cystic fibrosis patients

Joachim Hundrieser 1, Silvia Bremer 2, Frank Peinemann 3, Manfred Stuhrmann 4, Nicola Hoffknecht 1, Brigitte Wulf 2, Jiirg Schmidtke 4, Jochen Reiss 3, Giinter Maafi 2, and Burkhard Tiimmler 2

1Abteilung Humangenetik and 2Abteilung Biophysikalische Chemie, Medizinische Hochsehule, Konstanty-Gutschow-Strasse 8, D-3000 Hannover 61, Federal Republic of Germany 3Institut far Humangenetik der Universit~t, Gosslerstrasse 12d, D-3400 G6ttingen, Federal Republic of Germany 4Institut ftir Humangenetik, Freie Universit~t, Heubnerweg 6, D-1000 Berlin 19, Germany

Summary. The F508 deletion in the cystic fibrosis trans- membrane conductance regulator (CFTR) gene was found in 8 out of 30 Turkish cystic fibrosis (CF) chromosomes (27%). Five Turkish AF508 CF chromosomes were asso- ciated with the risk haplotype B in KM19 (2 allele)/XV2c (1 allele). In the Turkish population, cystic fibrosis is predominantly caused by mutations other than the F508 deletion.

Introduction and methods

We report the frequency of the AF508 mutation and of the haplotypes of linked D N A markers in cystic fibrosis (CF) patients from Turkey where CF is less common than in Europe, but more frequent than in non-Caucasian populations (Cutting et al. 1989).

Blood was collected from thirteen two-generation Turkish CF families and two further unrelated Turkish CF patients after informed consent had been obtained. The methods used for D N A analysis are reported in the Summary Table at the end of the study.

Results and discussion

The frequencies of CF-linked marker alleles on normal (N) and CF Turkish chromosomes are given in Table 1. The AF508 deletion in the cystic fibrosis t ransmembrane conductance regulator (CFTR) gene was observed less frequently in CF patients of Turkish ancestry than in the German (Reis et al., this issue) and Canadian CF popu- lations (Kerem et al. 1989b). Whereas the frequency of the mutation was determined to be 68% in 128 Canadian and 77% in 400 German CF chromosomes, the AF508 deletion was only detected in 8 out of 30 Turkish CF chromosomes (27%). Three Turkish CF patients were homozygous for the deletion, and 2 patients were het- erozygous. The AF508 mutation was not detected in 10 Turkish CF patients. Tables 2 and 3 provide information