Two novel null mutations in a Taiwanese cystic fibrosis patient and a survey of East Asian CFTR mutations

Cystic fibrosis (CF; OMIM number 219700) is one of the most common and life-shortening autosomal recessive disorders in Caucasians, with an incidence of 1 in 2,500 newborns [Welsh et al., 2001]. Its incidence is significantly reduced in Asian populations (1 in 90,000) [Wright and Morton, 1968]. Little is known about the spectrum of CFTR mutations in Asians. Data from the small number of reports indicated that a potentially large pool of Asian CF mutations are novel. The commercially available mutation panels are not suitable for screening Asian CF mutations. A more comprehensive mutation detectionmethod is necessary to search for the unknown mutations. Using recently developed temporal temperature gradient gel electrophoresis (TTGE) method [Wong et al., 2001; Alper et al., in press (to be published elsewhere)], a CF patient from Taiwan was found to be compound heterozygote for E7X and 989992insA novel null mutations. The patient was a 11⁄2-year-old boy who was born at 41 weeks of gestation with normal weight and unremarkablemedical history until 7months of agewhen he was admitted to hospital in Taiwan with severe vomiting and abdominal distension. He was diagnosed with acute gastroenteritis. At 1 year of age, he had severe cough, poor appetite, and sputum colonization with Pseudomonas aeruginosa. The diagnosis of CF was made when the patient was 2 years old, based on the recurrent respiratory tract infection with pneumonia, sputum colonization with Pseudomonas and Staphylococcus epidermis, mucosal pluggings, bronchiectasis, echogenic bowl, developmental delay, steatorrhea, and elevated sweat chloride (89mmol/L). Molecular analysis by Genzyme Genetics pan-ethnic 87 mutation panel did not reveal anyCFTRmutations. Since autopsy revealed evidence of CF in his deceased older sister, a comprehensive mutational analysis of the CFTR gene was felt necessary. CFTR exons and their flanking intron regions were amplified using 27 primer pairs followed by TTGE analysis [Wong et al., 2001]. Exons 1 and 6b that revealed abnormal TTGE banding patterns were sequenced (data not shown). Twomutationswere identified;G151T in exon 1 changes a glutamate at amino acid residue 7 to a stop codon, and 989-992 insertion A causes frameshift and a truncated CFTR protein of 306 amino acids. The intron 8 polythymidine and GT tract variants were found to be homozygous 7T and heterozygous 11/12 GT, both were unremarkable. Although the parents were unavailable for carrier testing, the finding of two deleterious mutations and the positive family history substantiates the diagnosis of CF in this patient. Unfortunately, the patient died before the mutations were identified. He was pancreatic insufficient. Since CF cases were rarely seen in Taiwan, the patient was not properly treated with enzyme supplement. The two mutations found in our patient have never been reported. The patient’s father is from Taiwan and the mother from Vietnam. A literature search found more than 80 documented cases of CF patients in East Asia [Macek et al., 1992; Wang et al., 1993; Crawford et al., 1995; Zielenski et al., 1995a; Hojo et al., 1997; Macek et al., 1997; Suwanjutha et al., 1998; Seki et al., 1999; Wagner et al., 1999; Yoshimura et al., 1999; Morokawa et al., 2000; Wu et al., 2000]. Approximately 50 caseswere reported in Japan and about 10 cases have been reported in patients from Taiwan and Mainland China [Seki et al., 1999]. Most of the patients have not been analyzed at themolecular level. Only 15 (including this study) had identified CFTR mutations (Table I). It is remarkable that the East Asian CF patients do not share any mutations with patients of other ethnic backgrounds. Even within the East Asians, the CFTR mutation spectrum of Chinese patients is distinct from that of Japanese patients (Table I) [Hojo et al., 1997; Macek et al., 1997; Seki et al., 1999; Yoshimura et al., 1999; Morokawa et al., 2000]. Most of the mutations are frameshift, splice sitemutations, or nonsensemutations that predict a CFTR protein with null activity. All patients presented classical CFphenotype (Table I)with elevated sweat chloride and pancreatic insufficiency. *Correspondence to: Dr. Lee-Jun C. Wong, Ph.D., Associate Professor, Institute for Molecular and Human Genetics, P.O. Box 571477, Georgetown University Medical Center, 3800 Reservoir Rd, NW M4000, Washington, DC 20057. E-mail: wonglj@georgetown.edu