Maternal ABCA1 genotype is associated with severity of Smith–Lemli–Opitz syndrome and with viability of patients homozygous for null mutations

The Smith–Lemli–Opitz syndrome (SLOS [MIM 270400]) is an autosomal recessive malformation syndrome that shows a great variability with regard to severity. SLOS is caused by mutations in the Δ7sterol-reductase gene (DHCR7), which disrupt cholesterol biosynthesis. Phenotypic variability of the disease is already known to be associated with maternal apolipoprotein E (ApoE) genotype. The aim of this study was to detect additional modifiers of the SLOS phenotype. We examined the association of SLOS severity with variants in the genes for ApoC-III, lecithin-cholesterol acyltransferase, cholesteryl-ester transfer protein, ATP-binding cassette transporter A1 (ABCA1), and methylene tetrahydrofolate reductase. Our study group included 59 SLOS patients, their mothers, and 49 of their fathers. In addition, we investigated whether ApoE and ABCA1 genotypes are associated with the viability of severe SLOS cases (n=21) caused by two null mutations in the DHCR7 gene. Maternal ABCA1 genotypes show a highly significant correlation with clinical severity in SLOS patients (P=0.007). The rare maternal p.1587Lys allele in the ABCA1 gene was associated with milder phenotypes. ANOVA analysis demonstrated an association of maternal ABCA1 genotypes with severity scores (logarithmised) of SLOS patients of P=0.004. Maternal ABCA1 explains 15.4% (R²) of severity of SLOS patients. There was no association between maternal ApoE genotype and survival of the SLOS fetus carrying two null mutations. Regarding ABCA1 p.Arg1587Lys in mothers of latter SLOS cases, a significant deviation from Hardy–Weinberg equilibrium (HWE) was observed (P=0.005). ABCA1 is an additional genetic modifier in SLOS. Modifying placental cholesterol transfer pathways may be an approach for prenatal therapy of SLOS.     

DHCR7 mutation carrier rates and prevalence of the RSH/Smith-Lemli-Opitz syndrome: where are the patients?

RSH/Smith-Lemli-Opitz (SLOS) is an inborn error of metabolism with protean manifestations. Its exact incidence and prevalence are not known; however, the carrier rate for the most frequently occurring mutation, the null mutation IVS8-1G > C, is approximately 1 in 100 for the Caucasian population in North America (1%) and possibly as high as 1 in 50 to 1 in 30 in Central European populations (2-3.3%). Based on the allele frequencies and the proportion of this mutation observed in various patient populations, the expected incidence of RSH/SLOS in those populations was calculated and reported to be between 1 in 1,590 and 1 in 17,000. However, around the world the observed prevalence and incidence are much lower than those calculated from the individual mutation carrier rates observed in any given population. The discrepancy between the expected incidence and prevalence can be explained only in part by the neonatal and infancy deaths of the most severely affected children with RSH/SLOS and the under ascertainment of mild and atypical cases at the mild end of the spectrum. RSH/SLOS may be responsible for a high number of miscarriages. Recent observations estimate the prevalence of SLOS at 16 weeks of gestation as similar to that observed at birth (approximately 1 in 60,000) suggesting that either reduced fertility of carrier couples or losses of affected embryos or fetuses in the first trimester play a significant role in reducing the second trimester prevalence of RSH/SLOS. It is possible that the estimates of carrier rates based on population screening for the most commonly occurring mutations may not reflect the true carrier rates in the population. In order to reconcile the above-mentioned paradoxes, we propose a model based on a higher than observed carrier frequency of the most common mutation and on very high fetal loss of homozygotes for that mutation.     

Identification of a novel 2026G→C mutation of the MRP2 gene in a Japanese patient with Dubin-Johnson syndrome

Dubin-Johnson syndrome is a recessive inherited disorder with conjugated hyperbilirubinemia caused by a dysfunction of multidrug resistance protein 2 (MRP2) on the canalicular membrane of hepatocytes. A mutational analysis of the MRP2 gene was carried out in three Japanese patients and their family members. In two patients, the homozygous mutations c.1901del67 and c,2272del168 were found. In the third patient, a –24CT polymorphism and the two mutations c.1901del67 and 2026GC were detected. The 2026GC mutation was a novel mutation in exon 16 affecting the conversion of Gly⁶⁷⁶ to Arg⁶⁷⁶ (G676R) in the MRP2 protein, and was not detected in fifty healthy volunteers. The G676R mutation was located in the Walker A motif of the first nucleotide binding domain in the MRP2 protein, and it was suggested that the mutation induced the dysfunction of the MRP2 protein. It was concluded that the compound heterozygosity of the two mutations of the MRP2 gene in the third patient contributed to the induction of hyperbilirubinemia in this case.     

The E148Q mutation in the MEFV gene: is it a disease-causing mutation or a sequence variant?

Familial Mediterranean fever (FMF) is an autosomal recessive disease characterized by recurrent attacks of serositis. To date more then 18 mutations responsible for the disease were identified in the MEFV gene, one such a mutation is E148Q in exon 2 of the gene. While screening FMF patients for mutations in the MEFV gene, we have identified 2 individuals parents of 2 unrelated FMF patients, who were homozygous for E148Q mutation. Upon clinical examination they were absolutely disease free and therefore raised the possibility that this mutation is a benign polymorphism rather than a mutation causing disease. To further investigate the role of the E148Q in FMF we analyzed 25 parents of FMF patients and a control group of 70 individuals, Jews of Moroccan extraction to match for ethnicity of the patients. The rate of E148Q in the control group was 6.4%, being 7.8% among the patient group. Among the parents group (obligatory carriers), in addition to the 2 parents that were homozygous E148Q, in 2 families one of the parents was heterozygote for E148Q but transmitted the other allele (apparently with unknown FMF mutation) to the affected child. Two healthy sibs of one of the E148Q homozygous were also homozygous E148Q. These observations are not in accordance to the notion that E148Q is a mutation causing disease.     

Sanfilippo type B syndrome: five patients with an R565P homozygous mutation in the α-N-acetylglucosaminidase gene from the Okinawa islands in Japan

Sanfilippo type B syndrome (mucopolysaccharidosis type IIIB; MPS IIIB) is an autosomal recessive lysosomal storage disorder that is caused by defective - N-acetylglucosaminidase (NAGLU). We performed NAGLU gene analysis in five patients with MPS IIIB whose respective parents from the Okinawa islands in Japan were not apparently consanguineous. We found a missense mutation (R565P) in all five patients (all homozygotes). We screened this mutation in 200 healthy subjects and found one heterozygote (none of the subjects were related to the patients). These results suggest that there may be a founder effect that results in the accumulation of R565P mutation in this area.     

Association analysis of Toll-like receptor 7 gene polymorphisms and Behçet's disease in Japanese patients

Action of Toll-like receptors (TLRs) is deeply associated with defense mechanisms of the innate and adaptive immune responses to microbial pathogens. There have been reports of genetic polymorphisms within the TLR7 gene being closely related to a variety of inflammatory and infectious diseases. Behçet's disease (BD) is an autoinflammatory disease, and the pathogenesis has yet to be fully discovered. We investigated whether polymorphisms of Toll-like receptor 7 (TLR7) are associated with BD by analyzing the frequency of eight single nucleotide polymorphisms (SNPs) within 200 Japanese BD patients and 102 randomized controls. We genotyped nine SNPs in the TLR7 gene and assessed the allele/genotype diversity between cases and controls for all SNPs. In all eight SNPs, statistically significant differences were not observed between cases and controls.     

Two mutations of the Gsα gene in two Japanese patients with sporadic pseudohypoparathyroidism type Ia

Pseudohypoparathyroidism Ia (PHP-Ia), is an inherited disease with clinical hypoparathyroidism caused by parathyroid hormone resistance (PTH), and shows the phenotype of Albright hereditary osteodystrophy (AHO), including short stature, obesity, round face, brachydactyly, and subcutaneous ossification. This disease is caused by mutation that inactivates the α-subunit of Gs, the stimulatory regulator of adenylyl cyclase. Here, a novel frameshift mutation (delG at codon 88) in exon 4, and a missense mutation (R231H) in exon 9 of the Gsα gene were identified in two Japanese patients with sporadic PHP-Ia. Deletion of a G in exon 4 at codon 88 in the first patient produced a premature stop codon, resulting in the truncated protein. The second patient had a previously reported R231H mutation. Because this amino acid is located in a region, switch 2, that is thought to interact with the βγ subunit of Gsα protein, this mutation may impair Gs protein function. We report here one novel Gsα mutation, and note that mutations in Japanese patients with PHP-Ia are probably heterogeneous. Received: November 27, 2000 / Accepted: March 21, 2001     

Identification of the first deep intronic mutation in the RPS6KA3 gene in a patient with a severe form of Coffin–Lowry syndrome

Coffin–Lowry syndrome (CLS) is an X-linked disorder characterized by growth and psychomotor retardation, hypotonia and progressive skeletal changes. RPS6KA3 is the only gene known to be associated with CLS, and over 150 distinct inactivating mutations in this gene have so far been reported in CLS patients. However, no defect is found in about half of the CLS compatible patients by exon sequencing. We report here the first deep intronic mutation in RPS6KA3, which is associated with the retention of intronic sequences in the mRNAs. Indeed, this finding suggests that all the patients with a highly suggestive CLS clinical diagnosis, but in whom exon screening has failed to detect a mutation, should be reanalyzed at the RNA level.     

Identification and molecular characterisation of a homozygous missense mutation in the ADAMTS10 gene in a patient with Weill–Marchesani syndrome

Weill–Marchesani syndrome is a rare disorder of the connective tissue. Functional variants in ADAMTS10 are associated with Weill–Marchesani syndrome-1. We identified a homozygous missense mutation, c.41T>A, of the ADAMTS10 gene in a 19-year-old female with typical symptoms of WMS1: proportionate short stature, brachydactyly, joint stiffness, and microspherophakia. The ADAMTS10 missense mutation was analysed in silico, with conflicting results as to its effects on protein function, but it was predicted to affect the leader sequence. Molecular characterisation in HEK293 Ebna cells revealed an intracellular mis-targeting of the ADAMTS10 protein with a reduced concentration of the polypeptide in the endoplasmic reticulum. A large reduction in glycosylation of the cytoplasmic fraction of the mutant ADAMTS10 protein versus the wild-type protein and a lack of secretion of the mutant protein are also evident in our results.In conclusion, we identified a novel missense mutation of the ADAMTS10 gene and confirmed the functional consequences suggested by the in silico analysis by conducting molecular studies.     

Duplication of exon 7–12 in the low-density lipoprotein receptor gene in three Danish patients with familial hypercholesterolemia

Familial hypercholesterolemia (FH) is one of the most frequent single-gene disorders; nevertheless, it is commonly underdiagnosed and undertreated. To increase the number of individuals diagnosed and treated for FH, an ongoing discovery of novel FH mutations is necessary as a prerequisite to implement good nationwide genetic FH screening strategies. Here we report on the finding of a seldom exon 7–12 duplication in the low-density lipoprotein receptor gene of three Danish patients with FH.     

Novel mutations, including the second most common in Japan, in the β-hexosaminidase α subunit gene, and a simple screening of Japanese patients with Tay-Sachs disease

Two novel mutations of the β-hexosaminidase α subunit gene were identified in Japanese patients with the infantile form of Tay-Sachs disease. One mutation was a one-base deletion at nt613C, which generated a stop codon at two codons downstream, in three unrelated patients. The other mutation was a one-base substitution of G-to-A at IVS 5, +1, which caused a splicing abnormality, in one patient. A missense mutation of R170W, which has already been reported in other ethnic groups, was also newly identified in one patient. In 1993, the most common mutation (IVS 5, −1G → T) in Japanese patients with Tay-Sachs disease was reported as the major mutation in Japan accounting for 80% of 56 mutant alleles from 28 unrelated patients. The deletion of nt613C was the second most common mutation, accounting for 5% of the mutant alleles. The previously reported mutation IVS 5, −1G → T and the nt613C deletion found in this study together accounted for 85% of the mutations causing Tay-Sachs disease among Japanese. Since these two mutations were located in or close to exon 6 and since they abolish Fok I (IVS 5, −1G → T) and Sfa NI (nt613C deletion) restriction sites, respectively, they were screened rapidly by single polymerase chain reaction followed by digestion with these enzymes. Received: November 10, 1998 / Accepted November 14, 1998     

Management of elderly patients with the Wolff-Parkinson-White syndrome: is less aggressive treatment justified?

Summary To study the age-related differences in Wolff-Parkinson-White syndrome an elderly group of 20 patients aged 40–65 years was compared to a younger group of 26 patients aged 18–39 years with respect to clinical profile and electrophysiological characteristics. The two groups were comparable in terms of the mechanism of reentry tachycardia, accessory pathway location, the number of patients reporting syncopal episodes, and the incidence of inducible and/or documented atrial flutter/fibrillation while only elderly patients had also atrial tachycardias. The elderly group was characterized by a higher incidence of associated organic heart disease and a significantly higher percentage of resuscitation from circulatory arrest. Cardiocirculatory arrest due to arrhythmias was the event leading to transferral to our hospital in 30% of elderly patients compared with 7.7% in the younger group. Analogous results were obtained when stratified according to the age at manifestation of tachyarrhythmias (< 30, 30 years), a history of cardiopulmonary resuscitation being the only significant difference between the two groups. There was no difference in any electrophysiologic parameter between the two age groups or with respect to the age at manifestation of arrhythmias. It is concluded that elderly patients with the Wolf-Parkinson-White syndrome should be managed as aggressively as their younger counterparts. In particular, manifestation of arrhythmias due to Wolff-Parkinson-White syndrome beyond age 30 should not be regarded as a more benign variation of the syndrome. Explanations for the more frequent history of resuscitation in the elderly include the presence of organic heart disease with impairment of left or right ventricular function and differences in the management of these patients.Abbreviation WPW Wolf-Parkinson-White syndrome     

Liddle's syndrome caused by a novel mutation of the γ-subunit of epithelial sodium channel gene SCNN1G in Chinese

Objective To screen the mutation of the β and γ subunits of epithelial sodium channel gene SCNN1 in two families with Liddle's syndrome. Methods Two patients clinically diagnosed as Liddle's syndrome and their family members were enrolled. Peripheral blood samples were collected and total genomic DNA was prepared. Polymerase chain reaction (PCR) was used to amplify the exon 13 of the SCNN1B and SCNN1G gene. PCR products were purified and subjected to direct DNA sequencing. Results A heterozygous nonsense mutation at codon 564 of the SCNN1B gene from CGA(Arg) to stop codon(TGA)was detector in the proband of family 1. More importantly, a novel heterozygous nonsense mutation of CAG (Gln) to stop codon TAG at codon 567 of the SCNN1G gene was detected in the proband and another two members of family 2. Conclusion Screening for specific mutations of the SCNN1 gene in relatives of patients with Liddle's syndrome can be used to identify the previously unrecognized cases within the family.A new nonsense mutation(Q567X) of the SCNN1G gene is likely the cause of Liddle's syndrome in family 2.     

Liddle's syndrome caused by a novel mutation of the γ-subunit of epithelial sodium channel gene SCNN1G in Chinese

Objective To screen the mutation of the β and γ subunits of epithelial sodium channel gene SCNN1 in two families with Liddle's syndrome. Methods Two patients clinically diagnosed as Liddle's syndrome and their family members were enrolled. Peripheral blood samples were collected and total genomic DNA was prepared. Polymerase chain reaction (PCR) was used to amplify the exon 13 of the SCNN1B and SCNN1G gene. PCR products were purified and subjected to direct DNA sequencing. Results A heterozygous nonsense mutation at codon 564 of the SCNN1B gene from CGA(Arg) to stop codon(TGA)was detector in the proband of family 1. More importantly, a novel heterozygous nonsense mutation of CAG (Gln) to stop codon TAG at codon 567 of the SCNN1G gene was detected in the proband and another two members of family 2. Conclusion Screening for specific mutations of the SCNN1 gene in relatives of patients with Liddle's syndrome can be used to identify the previously unrecognized cases within the family.A new nonsense mutation(Q567X) of the SCNN1G gene is likely the cause of Liddle's syndrome in family 2.