A Japanese patient homozygous for the H1085R mutation in the CFTR gene presents with a severe form of cystic fibrosis

To the Editor: Cystic fibrosis (CF), the most common autosomal recessive disorder in Caucasians, has long been believed to be extremely rare in Orientals (1, 2). In Japan, there have been approximately 130 cases of CF reported in the literature during the last 5 decades, with the estimated incidence of one in 350000 live births (3). Besides, very limited information is available about the spectrum of CF transmembrane conductance regulator (CFTR) gene mutations among Japanese CF patients, although more than 800 mutations of the CFTR gene, including the most common DF508, have been accumulated worldwide through the CF Genetic Analysis Consortium [(4), personal communication]. Here we describe a 15-year-old female Japanese patient who exhibited typical manifestations of CF and proved to be a homozygote for a very rare missense mutation H1085R. She was born to consanguineous parents at full term. From 1 year old, she repeatedly suffered from respiratory symptoms associated with Pseudomonas aeruginosa infection and experienced occasional steatorrhea. At 8 years old, she developed fecal ileus and underwent surgical operation. At 9 years old, she was diagnosed as CF based on the elevated sweat chloride level at 201 mmol/l. She also had chronic sinusitis, and abdominal ultrasonography revealed fibrotic changes of the pancreas. The patient has recently developed shortness of breath on exertion, and room-air arterial blood gas analysis showed moderate hypoxemia. For evaluation of the CFTR gene mutations, her DNA sample was evaluated for 32 major CFTR gene mutations responsible for more than 90% of CF chromosomes in the Caucasian population of North America (5). However, none of these mutations were detected in her CFTR alleles. Next, all 27 exons of the CFTR gene, including both the 5%and 3%-intron–exon junctions, were polymerase chain reaction (PCR) amplified and studied by single strand DNA conformation polymorphism (SSCP) analysis (6, 7). When the PCR products were electrophoresed and silver-stained, the DNA bands with different mobility from those of the control were only detected in exon 17b. Direct sequencing of the band clearly demonstrated an alteration of the nucleotide residue at 3386 from A to G in a homozygous fashion, resulting in His to Arg change at the amino acid 1085, a missense mutation H1085R. The CFTR genotype analysis of her family by PCR amplification of exon 17b and subsequent RsaI restriction digestion revealed that both parents and her three siblings were heterozygous for the mutation (Fig. 1). Further evaluation for three polymorphic loci proved that the H1085R mutation allele was associated with a haplotype of (GATT)6 in intron 6a (8), (TG)12T7 in the TG repeat and polythymidine tract at the splice acceptor site in intron 8 (9, 10), and M470 (1540A) in exon 10 (11, 12), respectively. The mutation H1085R, first described by Mercier et al. (13, 14), was detected on one of the CFTR alleles of a French CF patient who was pancreatic insufficient and a compound heterozygote with DF508 on the other chromosome [(13), personal communication]. However, no other CF patients with H1085R have been reported since then, implying that it is an extremely rare mutation (14). Consistent with the previous report that other mutations located in exon 17b, such as R1066L and M1101R, were usually associated with pancreatic insufficiency, the case presented here and the French case had pancreatic insufficiency, suggesting that the H1085R is also a severe allele [(13), personal communication]. Since the amino acid residue 1085 is located between the fourth and the fifth transmembrane segments of the second membrane-spanning domain and resides at the gate of the channel in the cytoplasm, it is conceivable that a His to Arg alteration would profoundly affect Cl conductance by either reduced Cl flow through a single open channel or by shortened duration for the channel opening (1, 15). One important point is that the H1085R alleles of these 2 patients are most likely to be recurrent