Mutations of the phenylalanine hydroxylase gene in patients with phenylketonuria in Shanxi, China.

The variation in mutations in exons 3, 6, 7, 11 and 12 of the phenylalanine hydroxylase (PAH) gene was investigated in 59 children with phenylketonuria (PKU) and 100 normal children. Three single nucleotide polymorphisms were detected by sequence analysis. The mutational frequencies of cDNA 696, cDNA 735 and cDNA 1155 in patients were 96.2%, 76.1% and 7.6%, respectively, whereas in healthy children the corresponding frequencies were 97.0%, 77.3% and 8.3%. In addition, 81 mutations accounted for 61.0% of the mutant alleles. R111X, H64 > TfsX9 and S70 del accounted for 5.1%, 0.8% and 0.8% mutation of alleles in exon 3, whereas EX6-96A > G accounted for 10.2% mutation of alleles in exon 6. R243Q had the highest incidence in exon 7 (12.7%), followed by Ivs7 + 2 T > A (5.1%) and T278I (2.5%). G247V, R252Q, L255S, R261Q and E280K accounted for 0.8% while Y356X and V399V accounted for 5.9% and 5.1%, respectively, in exon 11. R413P and A434D accounted for 5.9% and 2.5%, respectively, in exon 12. Seventy-two variant alleles accounted for the 16 mutations observed here. The mutation characteristics and distributions demonstrated that EX6-96A > G and R243Q were the hot regions for mutations in the PAH gene in Shanxi patients with PKU.

[Detection of exon 7 mutations of PAH gene in classical phenylketonuria by high-resolution melting analysis].

OBJECTIVE: To establish a simple, rapid, inexpensive and sensitive method for detecting hot region for mutations in exon 7 of PAH gene. METHODS: High-resolution melting (HRM) technology was used to detect a c.728G>A mutation in exon 7 in 88 patients with classical type phenylketonuria. Suspected mutations were validated by direct DNA sequencing. RESULTS: The results detected by HRM are in good agreement with the results obtained by direct sequencing. CONCLUSION: HRM analysis is a simple, rapid, inexpensive and sensitive method for detecting hot mutational region in exon 7 of PAH gene.

[Study on the mutations of phenylalanine hydroxylase gene in patients with phenylketonuria in Shanxi province].

OBJECTIVE: To study the mutations in exons 3, 6, 7, 11 and 12 of the phenylalanine hydroxylase gene (PAH) in Shanxi population. METHODS: The mutations in exons 3, 6, 7, 11 and 12 and flanking sequences of PAH gene were detected by PCR-DNA sequencing, in 59 patients with phynelketonuria(PKU) and 100 healthy children from Shanxi province. RESULTS: By sequence analysis, three single nucleotide polymorphism (SNP) Q232Q (CAA>CAG), V245V (GTG>GTA) and L385L (CTG>CTC) were detected in both the patients and healthy children, with the frequencies of nt 696, 735 and 1155 of the PAH cDNA up to 96.2%, 76.1% and 7.6% in patients respectively, and 97.0%, 77.3% and 8.3% respectively in the healthy controls. In addition, 72 different mutations accounting for 61.0% of mutant alleles were identified in the patients only. In exon 3, R111X, H64>TfsX9 and S70 del were found accounting for 5.1%, 0.8% and 0.8%; EX6-96A>G in exon 6 was found accounting for 10.2%. In exon 7, R243Q was the highest incidence accounting for 12.7%, followed by Ivs7+2 T>A(5.1%) and T278I(2.5%); the lowest incidences were G247V, R252Q, L255S, R261Q and E280K accounting for 0.8 %, respectively. In exon 11, Y356X (5.9%) and V399V (5.1%) were found; in exon 12, R413P and A434D were found accounting for 5.9% and 2.5%. In total, 9 missense mutations, 3 splice site mutations, 2 nonsense mutations and 2 deletions were included in 16 kinds of different mutations. CONCLUSION: The mutation characteristics and distribution in exons 3, 6, 7, 11 and 12 of the PAH gene have been identified, and it suggested that the EX6-96A>G and R243Q were the hot spots of PAH gene mutations in Shanxi PKU population.

Mitochondrial acetoacetyl-CoA thiolase (T2) deficiency: T2-deficient patients with "mild" mutation(s) were previously misinterpreted as normal by the coupled assay with tiglyl-CoA.

Mitochondrial acetoacetyl-CoA thiolase (T2) deficiency is an inborn error of metabolism that affects the catabolism of isoleucine and ketone bodies. This disorder is characterized by intermittent ketoacidotic episodes. Recently, we diagnosed T2 deficiency in two patients (GK45 and GK47) by the absence of potassium ion-activated acetoacetyl-CoA thiolase activity, whereas these patients were previously misinterpreted as normal by a coupled assay with tiglyl-CoA as a substrate. This method has been widely used for the enzymatic diagnosis of the T2 deficiency in the United States and Europe. We hypothesized that some residual T2 activity showed normal results in the assay. To prove this hypothesis, we analyzed these two patients together with three typical T2-deficient patients (GK46, GK49, and GK50) at the DNA level. Expression analysis of mutant cDNAs clearly showed that GK45 and GK47 had "mild" mutations (A132G, D339-V340insD) that retained some residual T2 activity, at least one of two mutant alleles, whereas the other three patients had null mutations (c.52-53insC, G152A, H397D, and IVS8+1g>t) in either allele. These results raise the possibility that T2-deficient patients with mild mutations have been misinterpreted as normal by the coupled assay with tiglyl-CoA.

Disruption of the BLM gene in ATM-null DT40 cells does not exacerbate either phenotype.

Bloom syndrome and ataxia-telangiectasia are autosomal recessive human disorders characterized by immunodeficiency, genome instability and predisposition to develop cancer. Recent data reveal that the products of these two genes, BLM and ATM, interact and function together in recognizing abnormal DNA structures. To investigate the function of these two molecules in DNA damage recognition, we generated double knockouts of ATM(-/-) BLM(-/-) in the DT40 chicken B-lymphocyte cell line. The double mutant cells were viable and exhibited a variety of characteristics of both ATM(-/-) and BLM(-/-) cells. There was no evidence for exacerbation of either phenotype; however, the more extreme radiosensitivity seen in ATM(-/-) and the elevated sister chromatid exchange seen in BLM(-/-) cells were retained in the double mutants. These results suggest that ATM and BLM have largely distinct roles in recognizing different forms of damage in DNA, but are also compatible with partially overlapping functions in recognizing breaks in radiation-damaged DNA.

Single base substitutions at the initiator codon in the mitochondrial acetoacetyl-CoA thiolase (ACAT1/T2) gene result in production of varying amounts of wild-type T2 polypeptide.

Initiator codon mutations are relatively uncommon and less well characterized compared to other types of mutations. We identified a novel initiator codon mutation (c.2T>C) heterozygously in a Japanese patient (Patient GK30) with mitochondrial acetoacetyl-CoA thiolase (T2) gene deficiency (ACAT1 deficiency); c.149delC was on the other allele. We examined translation efficiencies of nine mutant T2 cDNAs harboring one-base substitutions at the initiator methionine codon using in vivo transient expression analysis. We found that all the mutants produced wild-type T2 polypeptide, to various degrees (wild type (100%) > c.1A>C (66%) > c.2T>C, c.3G>C, c.3G>T (22%) > c3G>A, c.1A>G (11%) > c.2T>A, c.2T>G, c.1A>T (7.4%)). T2 mRNA expression levels in Patient GK08 (a homozygote of c.2T>A) and Patient GK30 fibroblasts, respectively, were almost the same as in control fibroblasts, when examined using semiquantitative PCR. This means that initiator codon mutations did not affect T2 mRNA levels. We propose that all one-base substitutions at the initiator methionine codon in the T2 gene could be mutations, which retain some residual T2 activity.