Pentanucleotide Repeat Insertions in RAI1 Cause Benign Adult Familial Myoclonic Epilepsy Type 8.

BACKGROUND: Benign adult familial myoclonic epilepsy (BAFME) is an autosomal dominant disorder characterized by cortical tremors and seizures. Six types of BAFME, all caused by pentanucleotide repeat expansions in different genes, have been reported. However, several other BAFME cases remain with no molecular diagnosis. OBJECTIVES: We aim to characterize clinical features and identify the mutation causing BAFME in a large Malian family with 10 affected members. METHODS: Long-read whole genome sequencing, repeat-primed polymerase chain reaction and RNA studies were performed. RESULTS: We identified TTTTA repeat expansions and TTTCA repeat insertions in intron 4 of the RAI1 gene that co-segregated with disease status in this family. TTTCA repeats were absent in 200 Malian controls. In the affected individuals, we found a read with only nine TTTCA repeat units and somatic instability. The RAI1 repeat expansions cause the only BAFME type in which the disease-causing repeats are in a gene associated with a monogenic disorder in the haploinsufficiency state (ie, Smith-Magenis syndrome [SMS]). Nevertheless, none of the Malian patients exhibited symptoms related to SMS. Moreover, leukocyte RNA levels of RAI1 in six Malian BAFME patients were no different from controls. CONCLUSIONS: These findings establish a new type of BAFME, BAFME8, in an African family and suggest that haploinsufficiency is unlikely to be the main pathomechanism of BAFME. © 2023 International Parkinson and Movement Disorder Society. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

A novel de novo COL1A1 mutation in a Thai boy with osteogenesis imperfecta born to consanguineous parents.

Osteogenesis imperfecta (OI) is genetically heterogeneous. Mutations in COL1A1 and COL1A2 are responsible for at least 90% of the cases, which are transmitted in an autosomal dominant manner or are de novo events. We identified a Thai boy with OI whose parents were first cousins. Because the proband was the product of a consanguineous marriage, we hypothesized that he might be homozygous for a mutation in a known gene causing a recessive form of OI. Using whole exome sequencing (WES), we did not find any pathogenic mutations in any known gene responsible for an autosomal recessive form of OI. Instead, we identified a COL1A1 frameshift mutation, c.1290delG (p.Gly431Valfs*110) in heterozygosis. By Sanger sequencing, the mutation was confirmed in the proband, and not detected in his parents, indicating that it was a de novo mutation. These findings had implication for genetic counseling. In conclusion, we expanded the mutational spectrum of COL1A1 and provided another example of a de novo pathogenic mutation in heterozygosis in a patient born to consanguineous parents.

Absent expression of the osteoblast-specific maternally imprinted genes, DLX5 and DLX6, causes split hand/split foot malformation type I.

BACKGROUND: Split hand/split foot malformation (SHFM) type 1 is characterised by missing central digital rays with clefts of the hands and/or feet, which was linked to chromosome 7q21.3. While double knockout of Dlx5 and Dlx6 resulted in limb defects in mice, the majority of patients with SHFM1 had only heterozygous chromosomal abnormalities. OBJECTIVE: To investigate the clinical and molecular features of a large family with SHFM1. METHODS: Blood samples of family members were investigated by linkage analysis, array comparative genomic hybridisation, exome sequencing and PCR-Sanger sequencing. Cultures from bone specimens obtained from the proband and an unrelated unaffected individual were established and subjected to quantitative real-time PCR, reverse-transcribed PCR, Western blot and imprinting analysis. RESULTS: We report a large pedigree of SHFM1 with 10 members having a heterozygous 103 kb deletion, the smallest one ever reported to be associated with SHFM1. Of these 10, two had no limb anomalies, making a penetrance of 80%. The deletion encompassed exons 15 and 17 of DYNC1I1, which are known enhancers of two downstream genes, DLX5 and DLX6. Surprisingly, DLX5 and DLX6 RNA and proteins in our proband's cultured osteoblasts, instead of 50% decrease, were absent. Allelic expression studies in cultured osteoblasts of the unaffected individual showed that DSS1, DLX6 and DLX5 expressed only paternal alleles. These lines of evidence indicate that DSS1, DLX6 and DLX5 were maternally imprinted in osteoblasts. CONCLUSIONS: SHFM1 in our family is caused by a heterozygous paternal deletion of enhancers of the osteoblast-specific maternally imprinted DLX6 and DLX5 genes, leading to the absence of their proteins.

Disorders with similar clinical phenotypes reveal underlying genetic interaction: SATB2 acts as an activator of the UPF3B gene.

Two syndromic cognitive impairment disorders have very similar craniofacial dysmorphisms. One is caused by mutations of SATB2, a transcription regulator and the other by heterozygous mutations leading to premature stop codons in UPF3B, encoding a member of the nonsense-mediated mRNA decay complex. Here we demonstrate that the products of these two causative genes function in the same pathway. We show that the SATB2 nonsense mutation in our patient leads to a truncated protein that localizes to the nucleus, forms a dimer with wild-type SATB2 and interferes with its normal activity. This suggests that the SATB2 nonsense mutation has a dominant negative effect. The patient's leukocytes had significantly decreased UPF3B mRNA compared to controls. This effect was replicated both in vitro, where siRNA knockdown of SATB2 in HEK293 cells resulted in decreased UPF3B expression, and in vivo, where embryonic tissue of Satb2 knockout mice showed significantly decreased Upf3b expression. Furthermore, chromatin immunoprecipitation demonstrates that SATB2 binds to the UPF3B promoter, and a luciferase reporter assay confirmed that SATB2 expression significantly activates gene transcription using the UPF3B promoter. These findings indicate that SATB2 activates UPF3B expression through binding to its promoter. This study emphasizes the value of recognizing disorders with similar clinical phenotypes to explore underlying mechanisms of genetic interaction.

A common and two novel GBA mutations in Thai patients with Gaucher disease.

Gaucher disease (GD) is an autosomal recessive disorder caused by mutations in the glucocerebrosidase (GBA) gene, leading to a deficiency of lysosomal ß-glucosidase and accumulation of glycosphingolipids in macrophages. We studied five Thai families with GD (four with GD type 1 and one with GD type 2). Using long-template PCR, PCR using specific primers for the functional gene, direct sequencing of all coding regions of GBA and restriction enzyme digestions, all 10 mutant alleles were successfully identified. The common c.1448T>C (p.L483P or L444P) mutation was identified in 60% of mutant alleles. Of the two patients homozygous for the p.L483P (L444P) mutation, one died from hepatic failure at age 16 years and the other died from sepsis at age 12 years. This p.L483P (L444P) mutation was found in four different haplotypes, suggesting that it was a recurrent mutation, not caused by a founder effect. Two novel mutations, a missense (c.1204T>C, p.Y402H), and a termination codon mutation (c.1609T>C, p.X537A) were found. Studies to determine the molecular pathomechanism of the p.X537A mutation, the first of its kind in this gene, showed that it decreased the amount of protein being expressed and the enzymatic activity, while it was still correctly localized.

Novel CTSK mutation resulting in an entire exon 2 skipping in a Thai girl with pycnodysostosis.

Pycnodysostosis is a rare autosomal recessive skeletal dysplasia characterized by osteosclerosis, short stature, acro-osteolysis of the distal phalanges, bone fragility and skull deformities. Mutations in the cathepsin K (CTSK) gene, which encodes a lysosomal cysteine protease highly expressed in osteoclasts, have been found to be responsible for the disease. We identified a Thai girl with pycnodysostosis. Her parents were first cousins. Polymerase chain reaction sequencing of the entire coding regions of CTSK of the proband's complementary DNA revealed that the whole exon 2 was skipped. We subsequently amplified exon 2 using genomic DNA, which showed that the patient was homozygous for a c.120G>A mutation. The mutation was located at the last nucleotide of exon 2. Its presence was confirmed by restriction enzyme analysis using BanI. The skipping of exon 2 eliminates the normal start codon. The mutation has never been previously reported, thus the current report expands the CTSK mutational spectrum.

FGFR1 and FGFR2 mutations in Pfeiffer syndrome.

Pfeiffer syndrome (PS) (MIM 101600) is one of the most common syndromic forms of craniosynostosis. It is characterized by craniosysnostosis, midface hypoplasia, broad and medially deviated thumbs, and great toes with partial syndactyly of the digits. Here, we described clinical and genetic features of 12 unrelated Thai individuals with PS. All 12 patients were sporadic, and advanced paternal age was found in 50% of the cases. Polymerase chain reaction sequencing of FGFR1 exon 5 and FGFR2 exons 8, 10, 15, 16, and 17 was performed in all PS patients and revealed 9 recurrent mutations in all patients. Most of the mutations clustered in exons 8 and 10 (9/12) accounting for 75% of PS cases. The most frequently detected mutation, p.S351C, was associated with the severe form of PS in the Thai population. Less frequent mutations in exons 16 (p.K641R) and 17 (p.G663E) were also identified. In addition, the p.P252R mutation in FGFR1 was detected in 1 PS patient with unilateral coronal craniosynostosis expanding the phenotypic spectrum of PS with this particular mutation. Knowing the mutation spectrum of the responsible genes could lead to the most effective strategy in identifying mutations causing Pfeiffer syndrome in the Thai population.

Nine patients with KCNQ2-related neonatal seizures and functional studies of two missense variants.

Mutations in KCNQ2 encoding for voltage-gated K channel subunits underlying the neuronal M-current have been associated with infantile-onset epileptic disorders. The clinical spectrum ranges from self-limited neonatal seizures to epileptic encephalopathy and delayed development. Mutations in KCNQ2 could be either gain- or loss-of-function which require different therapeutic approaches. To better understand genotype-phenotype correlation, more reports of patients and their mutations with elucidated molecular mechanism are needed. We studied 104 patients with infantile-onset pharmacoresistant epilepsy who underwent exome or genome sequencing. Nine patients with neonatal-onset seizures from unrelated families were found to harbor pathogenic or likely pathogenic variants in the KCNQ2 gene. The p.(N258K) was recently reported, and p. (G279D) has never been previously reported. Functional effect of p.(N258K) and p.(G279D) has never been previously studied. The cellular localization study demonstrated that the surface membrane expression of Kv7.2 carrying either variant was decreased. Whole-cell patch-clamp analyses revealed that both variants significantly impaired Kv7.2 M-current amplitude and density, conductance depolarizing shift in voltage dependence of activation, membrane resistance, and membrane time constant (Tau), indicating a loss-of-function in both the homotetrameric and heterotetrameric with Kv7.3 channels. In addition, both variants exerted dominant-negative effects in heterotetrameric with Kv7.3 channels. This study expands the mutational spectrum of KCNQ2- related epilepsy and their functional consequences provide insights into their pathomechanism.

Primary hyperoxaluria type 1 and brachydactyly mental retardation syndrome caused by a novel mutation in AGXT and a terminal deletion of chromosome 2.

Primary hyperoxaluria type 1 (PH1) is an autosomal recessive disorder caused by mutations in the alanine:glyoxylate aminotransferase (AGXT) gene, located on chromosome 2q37. Mutant AGXT leads to excess production and excretion of oxalate, resulting in accumulation of calcium oxalate in the kidney, and progressive loss of renal function. Brachydactyly mental retardation syndrome (BDMR) is an autosomal dominant disorder, caused by haploinsufficiency of histone deacetylase 4 (HDAC4), also on chromosome 2q37. It is characterized by skeletal abnormalities and developmental delay. Here, we report on a girl who had phenotypes of both PH1 and BDMR. PCR-sequencing of the coding regions of AGXT showed a novel missense mutation, c.32C>G (p.Pro11Arg) inherited from her mother. Functional analyses demonstrated that it reduced the enzymatic activity to 31% of the wild-type and redirected some percentage of the enzyme away from the peroxisome. Microsatellite and array-CGH analyses indicated that the proband had a paternal de novo telomeric deletion of chromosome 2q, which included HDAC4. To our knowledge, this is the first report of PH1 and BDMR, with a novel AGXT mutation and a de novo telomeric deletion of chromosome 2q.

Long-read Amplicon Sequencing of the CYP21A2 in 48 Thai Patients With Steroid 21-Hydroxylase Deficiency.

CONTEXT: Congenital adrenal hyperplasia is most commonly caused by 21-hydroxylase deficiency (21-OHD), an autosomal recessive disorder resulting from biallelic pathogenic variants (PVs) in CYP21A2. With a highly homologous pseudogene and various types of single nucleotide and complex structural variants, identification of PVs in CYP21A2 has been challenging. OBJECTIVE: To leverage long-read next-generation sequencing combined with locus-specific polymerase chain reaction (PCR) to detect PVs in CYP21A2 and to determine its diagnostic yield in patients with 21-OHD. METHODS: Forty-eight Thai patients with 21-OHD comprising 38 sporadic cases and 5 pairs of siblings were enrolled. Two previously described locus-specific PCR methods were performed. Amplicons were subject to long-read sequencing. RESULTS: Ninety-six PVs in CYP21A2 in the 48 patients were successfully identified. The combined techniques were able to detect 26 structural chimeric variants (27%; 26/96) in 22 patients with 18 having monoallelic and 4 having biallelic chimeras. The remaining PVs were pseudogene-derived mutations (63%; 60/96), entire gene deletions (2%; 2/96), missense variants (3%; 3/96), a splice-site variant (2%; 2/96), frameshift variants (2%; 2/96), and a nonsense variant (1%; 1/96). Notably, a splice-site variant, IVS7 + 1G > T, which was identified in a pair of siblings, has not previously been reported. CONCLUSIONS: Our approach exploiting locus-specific PCR and long-read DNA sequencing has a 100% diagnostic yield for our cohort of 48 patients with 21-OHD.

A LILRB1 variant with a decreased ability to phosphorylate SHP-1 leads to autoimmune diseases.

Inborn errors of immunity are known to cause not only immunodeficiencies and allergies but also autoimmunity. Leukocyte immunoglobulin-like receptor B1 (LILRB1) is a receptor on leukocytes playing a role in regulating immune responses. No phenotypes have been reported to be caused by germline mutations in LILRB1. We aimed to identify the causative variant in a three-generation family with nine members suffering from one of the three autoimmune diseases-Graves' disease, Hashimoto's thyroiditis, or systemic lupus erythematosus. Whole-genome linkage study revealed a locus on chromosome 19q13.4 with the maximum LOD score of 2.71. Whole-exome sequencing identified a heterozygous missense variant, c.479G > A (p. G160E) in LILRB1, located within the chromosomal-linked region, in all nine affected members. The variant has never been previously reported. Jurkat cells transfected with the mutant LILRB1, compared with those with the wild-type LILRB1, showed decreased phosphorylation of both LILRB1 and its downstream protein, SHP-1. Flow cytometry was used to study immunophenotype and revealed that LILRB1 was significantly lower on the surface of activated regulatory T lymphocytes (Treg) cells of patients. Single-cell RNA sequencing showed substantially increased M1-like monocytes in peripheral blood mononuclear cells of affected individuals. This study, for the first time, implicates LILRB1 as a new disease gene for autoimmunity.

Novel Variants and Phenotypes in NEUROG3-Associated Syndrome.

CONTEXT: Biallelic pathogenic variants in the NEUROG3 gene cause malabsorptive diarrhea, insulin-dependent diabetes mellitus (IDDM), and rarely hypogonadotropic hypogonadism. With only 17 reported cases, the clinical and mutational spectra of this disease are far from complete. OBJECTIVE: To identify the underlying genetic etiology in 3 unrelated Thai patients who presented with early-onset malabsorptive diarrhea, endocrine abnormalities, and renal defects and to determine the pathogenicity of the newly identified pathogenic variants using luciferase reporter assays and western blot. METHODS: Three unrelated patients with congenital diarrhea were recruited. Detailed clinical and endocrinological features were obtained. Exome sequencing was performed to identify mutations and in vitro functional experiments including luciferase reporter assay were studied to validate their pathogenicity. RESULTS: In addition to malabsorptive diarrhea due to enteric anendocrinosis, IDDM, short stature, and delayed puberty, our patients also exhibited pituitary gland hypoplasia with multiple pituitary hormone deficiencies (Patient 1, 2, 3) and proximal renal tubulopathy (Patient 2, 3) that have not previously reported. Exome sequencing revealed that Patient 1 was homozygous for c.371C > G (p.Thr124Arg) while the other 2 patients were homozygous for c.284G > C (p.Arg95Pro) in NEUROG3. Both variants have never been previously reported. Luciferase reporter assay demonstrated that these 2 variants impaired transcriptional activity of NEUROG3. CONCLUSIONS: This study reported pituitary gland hypoplasia with multiple pituitary hormone deficiencies and proximal renal tubulopathy and 2 newly identified NEUROG3 loss-of-function variants in the patients with NEUROG3-associated syndrome.

PTPRF is disrupted in a patient with syndromic amastia.

BACKGROUND: The presence of mammary glands distinguishes mammals from other organisms. Despite significant advances in defining the signaling pathways responsible for mammary gland development in mice, our understanding of human mammary gland development remains rudimentary. Here, we identified a woman with bilateral amastia, ectodermal dysplasia and unilateral renal agenesis. She was found to have a chromosomal balanced translocation, 46,XX,t(1;20)(p34.1;q13.13). In addition to characterization of her clinical and cytogenetic features, we successfully identified the interrupted gene and studied its consequences. METHODS: Characterization of the breakpoints was performed by molecular cytogenetic techniques. The interrupted gene was further analyzed using quantitative real-time PCR and western blotting. Mutation analysis and high-density SNP array were carried out in order to find a pathogenic mutation. Allele segregations were obtained by haplotype analysis. RESULTS: We enabled to identify its breakpoint on chromosome 1 interrupting the protein tyrosine receptor type F gene (PTPRF). While the patient's mother and sisters also harbored the translocated chromosome, their non-translocated chromosomes 1 were different from that of the patient. Although a definite pathogenic mutation on the paternal allele could not be identified, PTPRF's RNA and protein of the patient were significantly less than those of her unaffected family members. CONCLUSIONS: Although ptprf has been shown to involve in murine mammary gland development, no evidence has incorporated PTPRF in human organ development. We, for the first time, demonstrated the possible association of PTPRF with syndromic amastia, making it a prime candidate to investigate for its spatial and temporal roles in human breast development.

Dosage Optimization of Efavirenz Based on a Population Pharmacokinetic-Pharmacogenetic Model of HIV-infected Patients in Thailand.

PURPOSE: Efavirenz exhibits high interindividual variability in plasma concentrations, leading to unpredictable efficacy and toxicity. Polymorphism of CYP2B6 516G > T has been found to predominantly contribute to efavirenz variability. However, dosage recommendations incorporating CYP2B6 516G > T polymorphism have not been investigated in the Thai population. This study aimed to develop a population model of the pharmacokinetic properties of efavirenz, and to investigate the impact of patients' characteristics and CYP2B6 516G > T polymorphism on the pharmacokinetic properties of efavirenz. Model-based simulations were performed to provide genotype-based dosage optimization in a Thai population. METHODS: Plasma efavirenz concentrations measured at 12 h post-dose in 360 Thai HIV-infected patients with and without tuberculosis were analyzed by the nonlinear mixed-effects modeling approach. A 1-compartment model with first-order absorption and elimination was used for describing the pharmacokinetic properties of efavirenz. FINDINGS: The allele frequency of CYP2B6 516G > T was 34.17%. The efavirenz oral clearance were 11.9, 8.0, and 2.8 L/h in patients weighing 57 kg and having the CYP2B6 516 GG, 516 GT, and 516 TT genotypes, respectively. The use of rifampicin increased efavirenz oral clearance by 28%. The results from the simulations suggest that efavirenz dosages of 400, 300, and 100 mg once daily in Thai HIV mono-infected patients, and 800, 600, and 200 mg once daily in HIV/tuberculosis co-infected patients carrying CYP2B6 516 GG, 516 GT, and 516 TT, respectively. IMPLICATION: The results from this study provide a rationale for efavirenz dose adjustment based on CYP2B6 516G > T polymorphism in Thai HIV-infected patients, which could help to improve treatment outcomes in this population. ClinicalTrials.gov identifier: NCT01138267.

A patient with combined pituitary hormone deficiency and osteogenesis imperfecta associated with mutations in LHX4 and COL1A2.

Genetic disorders have been shown to co-occur in individual patient. A Thai boy with features of osteogenesis imperfecta (OI) and combined pituitary hormone deficiency (CPHD) was identified. The causative mutations were investigated by whole exome and Sanger sequencing. Pathogenicity and pathomechanism of the variants were studied by luciferase assay. The proband was found to harbor a novel de novo heterozygous missense mutation, c.1531G > T (p.G511C), in COL1A2 leading to OI and a heterozygous missense variant, c.364C > T (p.R122W), in LHX4. The LHX4 p.R122W has never been reported to cause CPHD. The variant was predicted to be deleterious and found in the highly conserved LIM2 domain of LHX4. The luciferase assays revealed that the p.R122W was unable to activate POU1F1, GH1, and TSHB promoters, validating its pathogenic effect in CPHD. Moreover, the variant did not alter the function of wild-type LHX4, indicating its hypomorphic pathomechanism. In conclusion, the novel de novo heterozygous p.G511C mutation in COL1A2 and the heterozygous pathogenic p.R122W mutation in LHX4 were demonstrated in a patient with OI and CPHD. This study proposes that the mutations in two different genes should be sought in the patients with clinical features unable to be explained by a mutation in one gene.

Generation of two human iPSC lines (MDCUi001-A and MDCUi001-B) from dermal fibroblasts of a Thai patient with X-linked osteogenesis imperfecta using integration-free Sendai virus.

Two clones of human induced pluripotent stem cells (iPSCs) were generated from dermal fibroblasts isolated from a one-year-old Thai patient with X-linked osteogenesis imperfecta. The patient harbored a mutation, p.N459S, in the MBTPS2 gene. The cells were reprogrammed using an integration-free Sendai virus containing KLF4, c-MYC, OCT4 and SOX2. Both of the established iPSC lines (MDCUi001-A and MDCUi001-B) maintained normal karyotype, expressed pluripotent markers and differentiated into all three germ layers.

Carbamazepine and phenytoin induced Stevens-Johnson syndrome is associated with HLA-B*1502 allele in Thai population.

PURPOSE: Previous studies found a strong association between HLA-B*1502 and carbamazepine (CBZ)-induced Stevens-Johnson syndrome (SJS) in Han Chinese, but not in Caucasian populations. Even in Han Chinese, the HLA-B*1502 was not associated with CBZ-induced maculopapular eruptions (MPE). This study seeks to identify whether HLA-B*1502 is associated with CBZ- or phenytoin (PHT)-induced SJS or MPE in a Thai population. METHODS: Eighty-one Thai epileptic patients between 1994 and 2007 from the Chulalongkorn Comprehensive Epilepsy Program were recruited. Thirty-one subjects had antiepileptic drug (AED)-induced SJS or MPE (6 CBZ-SJS, 4 PHT-SJS, 9 CBZ-MPE, 12 PHT-MPE), and 50 were AED-tolerant controls. RESULTS: For the first time, a strong association between HLA-B*1502 and PHT-induced SJS was found (p = 0.005). A strong association was also found between the HLA-B*1502 and CBZ-induced SJS (p = 0.0005), making Thai the first non-Chinese population demonstrating such an association. Some patients, who were HLA-B*1502 and suffered from CBZ-induced SJS, could be tolerant to PHT and vice versa. This suggests that HLA-B*1502 may be a common attribute required for a Thai patient to develop SJS from these two AEDs; other different elements, however, are also needed for each AED. In addition, no association between HLA-B alleles and CBZ- or PHT-induced MPE was found. CONCLUSIONS: CBZ- and PHT-induced SJS, but not MPE, is associated with HLA-B*1502 allele in Thai population.

Two novel EBP mutations in Conradi-Hünermann-Happle syndrome.

Conradi-Hünermann-Happle syndrome, also known as chondrodysplasia punctata type 2 (CDPX2), is an X-linked dominant disorder characterized by skin defects, skeletal and ocular abnormalities. CDPX2 was shown to be caused by mutations in the gene encoding emopamil binding protein (EBP). At least 58 different mutations have been described. Here we present clinical and molecular findings in two unrelated Thai girls with CDPX2. Mutation analysis by PCR-sequencing the entire coding region of EBP successfully revealed two potentially pathogenic, novel mutations, c.616G-->T and c.382delC. This study has expanded the spectrum of the EBP gene mutations causing CDPX2.

Nonsense mutations of the CYBB gene in two Thai families with X-linked chronic granulomatous disease.

X-linked chronic granulomatous disease (X-CGD) is an immunodeficiency disorder characterized by defective intracellular killing of microorganisms due to the neutrophils' inability to generate superoxide ions. Although it is always caused by mutations in the CYBB gene, clinical and molecular characteristics vary in different ethnic backgrounds. Two unrelated Thai boys presented with severe persistent pulmonary infections at the age of two months. Their abnormal dihydrorhodamine (DHR) flow cytometry assays supported the diagnosis of X-CGD. Mutation analysis was performed by polymerase chain reaction (PCR) amplification and sequencing of the entire coding regions of CYBB. Mutations identified were confirmed by restriction enzyme analyses. PCR-sequencing of the entire coding regions of CYBB identified nonsense mutations, 271C>T (R91X) in exon 4 and 456T>A (Y152X) in exon 5, in probands of each family. Both of the patients' mothers were found to be carriers. This observation supports that CYBB is the gene responsible for X-CGD across different populations and nonsense mutations are associated with severe phenotypes.