Henry J. Lin

Ethnic distribution of slow acetylator mutations in the polymorphic N-acetyltransferase (NAT2) gene.

The acetylation polymorphism may affect rates of activation or detoxification of common carcinogens, thereby influencing cancer risk. Our aim was to define the ethnic distribution of the major slow acetylator mutations in the polymorphic N-acetyltransferase gene, in order to provide background data for epidemiological studies. Our results contain new analyses on 803 individuals, including 365 new specimens and 438 specimens that had been partly characterized in an earlier study. Tests were done to establish the specificity and reproducibility (98%) of our PCR assays. The recognized slow acetylator mutations, 191A, 481T, 590A, and 857A (which correspond to alleles M4 and M4b; M1 and r3; M2/r2; and M3 and S3, respectively), accounted for nearly all slow acetylator alleles among blacks, whites, Asian Indians, Hispanics, Koreans, Japanese, Hong Kong Chinese, Taiwanese, Filipinos and Samoans. The ethnic distribution supports an interpretation that the acetylation polymorphism existed before Paleolithic splitting of human populations from Africa. We identified two additional NAT2 mutations, suggesting that other rare alleles are likely to be found.

Variants of N-acetyltransferase NAT1 and a case-control study of colorectal adenomas.

N-acetyltransferase NAT1, together with enzymes CYP1A2 and NAT2, helps convert heterocyclic amines to mutagens. Epidemiologic studies of the association of variants of these enzymes with colorectal cancer may provide indirect support for a heterocyclic amine mechanism. We used single strand conformation polymorphism and heteroduplex analysis to screen fro mutations in the NAT1 coding region in a case-control study (n = 932) of colorectal adenomas, which are precursors to cancer. Thirteen different single-base mutations were found: C97T, C190T, T402C, G445A-G459A-T640G ( a combination of three mutations), C559T, G560A, A613G, A752T, T777C, G781A, and A787G. Function of novel mutations was tested by bacterial production of enzymes and measurements of Km, Vmax, and stability. However, on 24-control individuals and 18 cases carried an inactivating NAT1 mutation. When combined with our data on the NAT2 acetylation polymorphism, we saw no evidence for an association between N-acetyltransferases and prevalence of adenomas. Larger sample sizes are required for further evaluation.

Chromosome 2q terminal deletion: Report of 6 new patients and review of phenotype-breakpoint correlations in 66 individuals

We report a new patient with terminal deletion of chromosome 2 with breakpoint at 2q36 and five additional new patients with 2q terminal deletion with breakpoint at 2q37. Hemidiaphragmatic hernia is a novel finding in one patient with a breakpoint at 2q37.1. In comparing these patients to 60 previously reported individuals with 2q terminal deletions, certain physical abnormalities are loosely associated with positions of breakpoint. For example, facial features (e.g., prominent forehead, depressed nasal bridge, and dysmorphic ears and nose), short stature, and short hands and feet were frequent in patients with breakpoints at or proximal to 2q37.3. Reports of horseshoe kidney and Wilms tumor were limited to patients with a breakpoint at 2q37.1, and structural brain anomalies and tracheal anomalies were reported only in patients with breakpoints at or proximal to 2q37.1. Cleft palate was reported only in patients with the most proximal breakpoints (2q36 or 2q35). Neurological effects including developmental delay, mental retardation, autistic‐like behavior, and hypotonia were typical in this patient population but did not stratify in severity according to breakpoint. Terminal deletion of the long arm of chromosome 2 should be considered in the infant with marked hypotonia, poor feeding, gastroesophageal reflux, and growth delay, and the older child with developmental delay, autistic behavior, and the characteristic facial and integumentary features described herein. Assignment of clinical features to specific breakpoints and refinement of predictive value may be useful in counseling.

Breast cancer, passive and active cigarette smoking and N-acetyltransferase 2 genotype.

The relationship of breast cancer to cigarette smoking is inconsistent in the literature, possibly due in part to heterogeneity in carcinogen metabolism. N-acetyltransferase 2 (NAT2) enzyme activity is believed to play a role in the activation of tobacco smoke carcinogens. We examined the effect of NAT2 genetic polymorphisms on risk of breast cancer from active and passive smoking. Women were recruited from those who had suspicious breast masses detected clinically and/or mammographically. Questionnaire data were collected prior to biopsy diagnosis to blind subjects and interviewers. Histopathology showed 113 cases with mammary carcinoma (30 carcinoma in situ) and 278 controls with benign breast disease. NAT2 genotype was determined using allele-specific polymerase chain reaction amplification to detect slow acetylator mutations. Effects of passive and active tobacco smoke and of NAT2 genotype on breast cancer risk were examined with logistic regression controlling for known risk factors. Models first included all controls, and subsequently 107 with no or low risk (normal breast or no hyperplasia), and finally 148 with high risk (hyperplasia, atypical hyperplasia, complex fibroadenomas). Referents had no active or passive smoke exposure. We found no association between breast cancer risk and NAT2, smoking status (never, former, current), smoking duration, or cigarettes per day. There were no effects of passive exposure among never-smokers. Models were unchanged across control groups. There were no statistical interactions between tobacco smoke exposure and NAT2. The results were similar when restricting the analysis to invasive cancers. These findings do not support the hypothesis that NAT2 is a risk factor for breast cancer or that it alters susceptibility to tobacco smoke.

Hematopoietic Prostaglandin D Synthase Suppresses Intestinal Adenomas in ApcMin/+ Mice

Aspirin and other nonsteroidal anti-inflammatory drugs prevent some cases of colon cancer by inhibiting prostaglandin (PG) synthesis. PGE(2) promotes colon neoplasia, as shown by knockout mouse studies on enzymes and receptors in the PG cascade. A few experiments 20 to 30 years ago suggested that PGD(2) may suppress tumors, but a role for biosynthetic enzymes for PGD(2) in tumor development has not been studied. We report here that disruption of the gene for hematopoietic PGD synthase in Apc(Min/+) mice led to approximately 50% more intestinal adenomas compared with controls. Tumor size was not affected. By immunohistochemistry, we detected hematopoietic PGD synthase mainly in macrophages and monocytes of the gut mucosa. The mean number of tumors did not increase with knockout of the gene for the lipocalin type of the enzyme, which is not produced in the intestine. On the other hand, Apc(Min/+) mice with transgenic human hematopoietic PGD synthase tended to have 80% fewer intestinal adenomas. The transgene produced high mRNA levels (375-fold over endogenous). There was a suggestion of higher urinary excretion of 11beta-PGF(2alpha) and a lower excretion of a PGE(2) metabolite in transgenic mice, but differences (30-40%) were not statistically significant. The results support an interpretation that hematopoietic PGD synthase controls an inhibitory effect on intestinal tumors. Further studies will be needed to prove possible mechanisms, such as routing of PG production away from protumorigenic PGE(2) or inhibition of the nuclear factor-kappaB cascade by PGD(2) metabolites.

Anomalous inferior and superior venae cavae with oculoauriculovertebral defect: Review of Goldenhar complex and malformations of left‐right asymmetry

We observed a girl with an interrupted, left inferior vena cava with hemiazygous continuation, bilateral superior venae cavae, heart defects, and sacral agenesis. She had macrostomia and bilateral ear tags and pits, as in oculoauriculovertebral defect. Maternal diabetes was present. The combination, which we call OAV-heterotaxia complex, supports the view that some cases of oculoauriculovertebral defect may be part of a midline field defect of blastogenesis.

Intrachromosomal triplication of 2q11.2-q21 in a severely malformed infant: case report and review of triplications and their possible mechanism.

A female fetus with brain malformations, multicystic kidneys, absence of the right thumb, and a posterior cleft of palate was delivered at 32 weeks of gestation. Cytogenetic studies including FISH showed a novel intrachromosomal triplication of the proximal long arm of chromosome 2 (q11.2-q21), resulting in tetrasomy for this segment. The middle repeat was inverted. At least 11 patients with intrachromosomal triplications have been reported, mostly involving chromosome 15q. The mechanism involved in formation of these rearrangements is compatible with U-type exchange events among three chromatids.

Genetic Risk Prediction of Atrial Fibrillation

Background: Atrial fibrillation (AF) has a substantial genetic basis. Identification of individuals at greatest AF risk could minimize the incidence of cardioembolic stroke. Methods: To determine whether genetic data can stratify risk for development of AF, we examined associations between AF genetic risk scores and incident AF in 5 prospective studies comprising 18 919 individuals of European ancestry. We examined associations between AF genetic risk scores and ischemic stroke in a separate study of 509 ischemic stroke cases (202 cardioembolic [40%]) and 3028 referents. Scores were based on 11 to 719 common variants (≥5%) associated with AF at P values ranging from <1×10−3 to <1×10−8 in a prior independent genetic association study. Results: Incident AF occurred in 1032 individuals (5.5%). AF genetic risk scores were associated with new-onset AF after adjustment for clinical risk factors. The pooled hazard ratio for incident AF for the highest versus lowest quartile of genetic risk scores ranged from 1.28 (719 variants; 95% confidence interval, 1.13–1.46; P=1.5×10−4) to 1.67 (25 variants; 95% confidence interval, 1.47–1.90; P=9.3×10−15). Discrimination of combined clinical and genetic risk scores varied across studies and scores (maximum C statistic, 0.629–0.811; maximum &Dgr;C statistic from clinical score alone, 0.009–0.017). AF genetic risk was associated with stroke in age- and sex-adjusted models. For example, individuals in the highest versus lowest quartile of a 127-variant score had a 2.49-fold increased odds of cardioembolic stroke (95% confidence interval, 1.39–4.58; P=2.7×10−3). The effect persisted after the exclusion of individuals (n=70) with known AF (odds ratio, 2.25; 95% confidence interval, 1.20–4.40; P=0.01). Conclusions: Comprehensive AF genetic risk scores were associated with incident AF beyond associations for clinical AF risk factors but offered small improvements in discrimination. AF genetic risk was also associated with cardioembolic stroke in age- and sex-adjusted analyses. Efforts are warranted to determine whether AF genetic risk may improve identification of subclinical AF or help distinguish between stroke mechanisms.

Asymptomatic maternal combined homocystinuria and methylmalonic aciduria (cblC) detected through low carnitine levels on newborn screening.

A symptom-free woman gave birth to a girl with a low carnitine level on newborn screening. The baby was unaffected, but the mother had biochemical abnormalities and mutations characteristic of the cblC defect of vitamin B(12) metabolism (late-onset form). This patient with cblC was detected through her infants newborn screening.

Mosaic tetrasomy 8q: Inverted duplication of 8q23.3qter in an analphoid marker

We observed an analphoid marker chromosome stable through cell division in a 16-year-old girl with developmental delay, short stature, limb contractures, and ovaries containing multiple cysts. She also developed myasthenia gravis at 15 years. The marker chromosome, present in 75% of metaphases (and in 90% of transformed lymphoblastoid cells), was C-band negative, and had no pan alpha-satellite sequences detectable by fluorescence in situ hybridization (FISH). The 8q origin of the marker was determined by use of subtelomeric probes and was confirmed by chromosome 8 painting probes. The marker was shown to be an inversion duplication of 8q when subtelomeric, telomeric, and c-myc FISH probes hybridized to both ends of the marker. The karyotype was 47,XX,+inv dup(8)(qter--> q23.3::q23.3-->[neocen]-->qter), resulting in tetrasomy for 8q23.3qter. The parents had normal karyotypes. Centromeric proteins CENP-C and CENP-E were present, but alpha associated centromere protein CENP-B was absent at a position defining a neocentromere.