Heteroplasmy levels of mtDNA1555A>G mutation is positively associated with diverse phenotypes and mutation transmission in a Chinese family.

The mtDNA 1555A>G mutation was considered to be one of the most common causes of aminoglycoside-induced and non-syndromic hearing loss. However, this mutation was always found in homoplasmy with high phenotypic heterogeneity. Recently this mutation in heteroplasmy has been reported in several studies. In the present study, we have collected a large Chinese family harboring heteroplasmic mtDNA 1555A>G mutation with diverse clinical phenotypes. To investigate the relationship between the mutation load and the severity of hearing loss under Eastern Asian background, we performed clinical, molecular, genetic and phylogenic analysis. This pedigree was characterized by coexistence of eight subjects with homoplasmic mutation and ten subjects with various degrees of heteroplasmy, and the results suggested that there was a strong correlation between the mutation load and the severity/age-onset of hearing loss (r=0.758, p<0.001). We noticed that the mutation level of offspring was associated with their mothers' in this pedigree, which indicated that maybe exist a regular pattern during the process of the heteroplasmic transmission. In addition, analysis of the complete mtDNA genome of this family revealed that it belonged to Eastern Asian haplogroup B4C1. In addition, a rare homoplasmic mtDNA 9128T>C variant was identified, it located at a strictly conserved site of mtDNA ATP6 gene.

[GJB2 gene mutation in deaf patients].

OBJECTIVE: To detect the GJB2 gene mutation in patients with autosomal-recessive deafness, and analyze the relationship between clinical phenotype and gene mutation. METHODS: Forty-two patients were examined clinically by pure tone audiometry, acoustic impedance and auditory brainstem response. The complete coding region of the GJB2 gene was amplified by polymerase chain reaction (PCR) and the PCR products were subjected to automatic DNA sequencing. RESULTS: Two cases had homozygous mutation of 235delC. One of them had sensorineural hearing loss while the other had mixed hearing loss. Heterozygous mutation of 176del16bp was detected in a pair of twins who had mixed hearing loss. The 109G to A, 79G to A and 341A to G mutations were observed in both the patients and the controls. CONCLUSION: Homozygous 235delC mutation is one of the pathogeni c mutations which could occur in patients with mixed hearing loss. The heterozygous 176del16bp mutation combined with environmental factor may cause hearing loss. The 109G to A, 79G to A and 341A to G variants were considered to be polymorphisms of the GJB2 gene.

A complex heterozygous mutation of His373Leu and Asp487-Ser488-Phe489 deletion in human cytochrome P450c17 causes 17alpha-hydroxylase/17,20-lyase deficiency in three Chinese sisters.

Cytochrome P450c17 deficiency is one of the rare forms of enzyme disorders in steroid biosynthesis, resulting from defects in 17alpha-hydroxylase and 17,20-lyase activities. The disease is caused by the mutations in CYP17 gene, inherited in an autosomal recessive pattern. We reported a Chinese family with three sisters suffering from P450c17 deficiency based on their clinical features and molecular genetics. The patients were found to be compound heterozygotes with two different mutations. Screened by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP), a heterozygous point mutation His373Leu was detected in the exon 6 of CYP17 gene which was proved to be derived from paternal allele. The other allele contained nine-base pair deletion, located in exon 8, eliminating codons 487-489 (Asp-Ser-Phe) near the carboxy-terminus of P450c17. The mother and the brother have been demonstrated to be carriers of deletion mutation through restriction enzyme analysis. Both mutations have been reported previously in Asia. This is the first report of the molecular genetic study of 17alpha-hydroxylase/17,20-lyase deficiency in mainland China with a novel compound heterozygous mutation.

Amino acid substitutions in the pore affect the anomalous mole fraction effect of CaV1.2 channels.

The anomalous mole fraction effect (AMFE) is an important indicator of ion-ion interactions in the pore of voltage-gated Ca2+ channels (VGCCs). The residues at position 1144 that differ in several classes of VGCCs are important to the permeation of the pore. Phe-1144 (F, CaV1) was substituted with glycine (G, CaV2) and lysine (K, CaV3) and the effects of mutation on the voltage and concentration dependency of AMFE were observed. Whole-cell currents were recorded in external solutions with Ca2+ and Ba2+ at the indicated ratios with a total divalent cation concentration of 2, 10 or 20 mM, at holding potentials from -80 to -20 mV. Results showed the ratio of Ba2+ to Ca2+ currents determined at 2 mM to be different from that determined under higher concentrations for wild-type channels but this ratio was not different when tail currents were evoked at different potentials. AMFE was greatest at relatively positive potentials (-20 mV) and when the total divalent cation concentrations were kept low (2 mM). AMFE was attenuated for F/G while it was accentuated for F/K compared with wild-type, respectively. The results demonstrated that glycine and lysine substitutions of Phe-1144 affect AMFE through different mechanisms. Additionally, residues at position 1144 were shown to be major determinates of channel permeation of several classes of VGCCs.

Mitochondrial DNA polymorphisms in Gelao ethnic group residing in Southwest China.

Gelao ethnic group, an aboriginal population residing in southwest China, has undergone a long and complex evolutionary process. To investigate the genetic structure of this ancient ethnic group, mitochondrial DNA (mtDNA) polymorphisms of 102 Gelao individuals were collected and analyzed in this study. With the aid of the information extracted from control-region hypervariable segments (HVSs) I and II as well as some necessary coding-region segments, phylogenetic status of all mtDNAs under study were determined by means of classifying into various defined haplogroups. The southern-prevalent haplogroups B, R9, and M7 account for 45.1% of the gene pool, whereas northern-prevalent haplogroups A, D, G, N9, and M8 consist of 39.2%. Haplogroup distribution indicates that the Gelao bears signatures of southern populations and possesses some regional characters. In the PC map, Gelao clusters together with populations with Bai-Yue tribe origin as well as the local Han and the Miao. The results demonstrate the complexity of Gelao population and the data can well supplement the China mtDNA database.

Analysis of mitochondrial DNA polymorphisms in Guangdong Han Chinese.

Previous investigations on Chinese mitochondrial DNA (mtDNA) variation revealed that the matrilineal gene pool of southern Han Chinese is rather complex, with much higher genetic diversity and more basal/ancient lineages than the northern Hans. The extreme case is Guangdong Han populations, among which pronounced (matrilineal) differentiation has been observed, indicative of complex demography of the region. To get more insights into the maternal makeup of southern Han Chinese, mtDNA variation of a total of 106 individuals sampled from Dongguan, Guangdong Province, China, was analyzed in this study. With the aid of the information from control-region hypervariable segments I and II (HVS-I and -II) as well as some necessary coding-region segments, the phylogenetic status of all mtDNAs under examination were determined according to the reconstructed East Asian mtDNA tree. In this way, the mtDNAs have been classified into various haplogroups or sub-haplogroups. The southern-prevalent haplogroups, such as R9 (20.8%), B (17.9%), M7b (14.2%), show relatively high distribution frequencies in Dongguan Hans; whereas the frequencies of Northern-prevalent haplogroups (with the exception of D) are quite low: C (1.9%), G2 (1.9%) and Z (1.9%), indicating the southern-origin of Dongguan Hans.