Double outlet right ventricle: aetiologies and associations.

BACKGROUND: Double outlet right ventricle (DORV), a clinically significant congenital heart defect, occurs in 1-3% of individuals with congenital heart defects. In contrast to other major congenital heart defects, there are no systematic or comprehensive data regarding associations, aetiologies, and pathogenesis of DORV. We analysed reported cases in the medical literature to address these issues. METHODS: We queried the PubMed database using key words "double outlet right ventricle" and "DORV" for case reports, epidemiologic analyses and animal studies with this cardiac anomaly. The anatomic subtype of DORV was classified according to criteria of Van Praagh. RESULTS: Chromosomal abnormalities were present in 61 of the 149 cases of DORV. Trisomies 13 and 18, and del 22q11 were the most commonly associated cytogenetic lesions; different anatomic subtypes of DORV were noted in trisomies 13 and 18 versus del 22q11. DORV was reported in many uncommon or rare non-chromosomal syndromes. Mutations and non-synonymous sequence variants in the CFC1 and CSX genes were the most commonly reported monogenic loci associated with DORV in humans; numerous genes are reported in murine models of DORV. Animal studies implicate maternal diabetes and prenatal exposure to ethanol, retinoids, theophylline, and valproate in DORV teratogenesis. CONCLUSIONS: The large number of genes associated with DORV in both humans and animal models and the different anatomic subtypes seen in specific aetiologies indicate the likelihood of several distinct pathogenetic mechanisms for DORV, including impairment of neural crest derivative migration and impairment of normal cardiac situs and looping.

Late-onset Tay-Sachs disease: adverse effects of medications and implications for treatment.

The authors conducted a retrospective and brief prospective study of adverse effects of approximately 350 medications in 44 adults with late-onset Tay-Sachs disease (LOTS). Some medications were relatively safe, whereas others, particularly haloperidol, risperidone, and chlorpromazine, were associated with neurologic worsening.

A seat at the table: membership in federal advisory committees evaluating public policy in genetics.

OBJECTIVES: This study examined who participates in federal government advisory committees regarding public policy in human and medical genetics, what parties they represent, and to what extent the general public is meaningfully represented. METHODS: Analysis focused on 7 federal government documents published from January 1990 to February 1995. Advisors were categorized into 4 groups based on the professional affiliations that were listed in the publications. After a search of several references and data-bases, the study examined whether these individuals also had other affiliations not listed in the government publications. RESULTS: Individuals whose principal affiliations were with academia (n = 32; 44%) or industry (n = 19; 26%) represented nearly three fourths of the sample, followed by government employees (n = 13; 18%) and consumer advocates (n = 8; 11%). At least 16% of the advisors serving on the federal committees, mostly members of academia, had a dual affiliation. CONCLUSIONS: These data indicate that the public has modest representation on key federal advisory committees making policy recommendations regarding human genetics technology and clinical practice and that there is ample room for additional public participation.

Mutations in HYAL1, a member of a tandemly distributed multigene family encoding disparate hyaluronidase activities, cause a newly described lysosomal disorder, mucopolysaccharidosis IX.

Hyaluronan (HA), a large glycosaminoglycan abundant in the extracellular matrix, is important in cell migration during embryonic development, cellular proliferation, and differentiation and has a structural role in connective tissues. The turnover of HA requires endoglycosidic breakdown by lysosomal hyaluronidase, and a congenital deficiency of hyaluronidase has been thought to be incompatible with life. However, a patient with a deficiency of serum hyaluronidase, now designated as mucopolysaccharidosis IX, was recently described. This patient had a surprisingly mild clinical phenotype, including notable periarticular soft tissue masses, mild short stature, an absence of neurological or visceral involvement, and histological and ultrastructural evidence of a lysosomal storage disease. To determine the molecular basis of mucopolysaccharidosis IX, we analyzed two candidate genes tandemly distributed on human chromosome 3p21.3 and encoding proteins with homology to a sperm protein with hyaluronidase activity. These genes, HYAL1 and HYAL2, encode two distinct lysosomal hyaluronidases with different substrate specificities. We identified two mutations in the HYAL1 alleles of the patient, a 1412G --> A mutation that introduces a nonconservative amino acid substitution (Glu268Lys) in a putative active site residue and a complex intragenic rearrangement, 1361del37ins14, that results in a premature termination codon. We further show that these two hyaluronidase genes, as well as a third recently discovered adjacent hyaluronidase gene, HYAL3, have markedly different tissue expression patterns, consistent with differing roles in HA metabolism. These data provide an explanation for the unexpectedly mild phenotype in mucopolysaccharidosis IX and predict the existence of other hyaluronidase deficiency disorders.

A unique familial leukodystrophy with adult onset dementia and abnormal glycolipid storage: a new lysosomal disease?

Two adult siblings with early onset dementia are described. At presentation, in their early 30s, they showed poor judgment and disinhibition. A progressive dementia ensued over several years. Brain MRI disclosed diffusely increased T2 signal in the cerebral white matter, suggestive of a leukodystrophy. Numerous lysosomal enzyme assays including leucocyte arylsulphatase A and galactocerebrosidase activities, plasma and fibroblast very long chain fatty acid concentrations, and urinary sulphatide concentrations were normal, as were CSF analyses. A brain biopsy disclosed periodic acid Schiff (PAS) and Sudan black positive material in perivascular macrophages which, by electron microscopy, consisted of stacks of straight or curvilinear paired membranes within angulate lysosomes, indicative of abnormal glycolipid accumulation. The combination of clinical, radiological, biochemical, and pathological features of this degenerative disease is not consistent with that of any of the known leukodystrophies or lysosomal storage disorders. These findings suggest a previously undescribed familial glycolipid storage disorder causing an adult onset leukodystrophy and presenting with behavioural symptoms that mimic a psychiatric disorder.

Public participation in medical policy-making and the status of consumer autonomy: the example of newborn-screening programs in the United States.

OBJECTIVES: State newborn-screening programs collectively administer the largest genetic-testing initiative in the United States. We sought to assess public involvement in formulating and implementing medical policy in this important area of genetic medicine. METHODS: We surveyed all state newborn-screening programs to ascertain the screening tests performed, the mechanisms and extent of public participation, parental access to information, and policies addressing parental consent or refusal of newborn screening. We also reviewed the laws and regulations of each state pertaining to newborn screening. RESULTS: Only 26 of the 51 state newborn-screening programs reported having advisory committees that include consumer representation. Fifteen states reported having used institutional review boards, another venue for public input. The rights and roles of parents vary markedly among newborn-screening programs in terms of the type and availability of screening information as well as consent-refusal and follow-up policies. CONCLUSIONS: There is clear potential for greater public participation in newborn-screening policy-making. Greater public participation would result in more representative policy-making and could enhance the quality of services provided by newborn-screening programs.

Palmitoyl-protein thioesterase deficiency in fibroblasts of individuals with infantile neuronal ceroid lipofuscinosis and I-cell disease.

Mutations in the gene encoding a recently described lysosomal enzyme, palmitoyl-protein thioesterase (PPT), have recently been shown to result in the neurodegenerative disorder, infantile neuronal ceroid lipofuscinosis (INCL). Reduced palmitoyl-protein thioesterase enzyme has been demonstrated previously in INCL brain and immortalized lymphoblasts. In the current paper, we demonstrate that: (1) PPT can be detected by immunoblotting and enzyme activity assays in normal human skin fibroblasts; (2) INCL fibroblasts are deficient in PPT activity; (3) I-cell disease fibroblasts show markedly reduced intracellular levels of PPT but markedly increased levels of PPT in cell culture medium. These data establish that PPT is transported to lysosomes via the lysosomal enzyme:lysosomal enzyme receptor phosphomannosyl recognition system under normal physiological conditions and provide the basis for a useful clinical assay for INCL.

Novel mutations and DNA-based screening in non-Jewish carriers of Tay-Sachs disease.

We have evaluated the feasibility of using PCR-based mutation screening for non-Jewish enzyme-defined carriers identified through Tay-Sachs disease-prevention programs. Although Tay-Sachs mutations are rare in the general population, non-Jewish individuals may be screened as spouses of Jewish carriers or as relatives of probands. In order to define a panel of alleles that might account for the majority of mutations in non-Jewish carriers, we investigated 26 independent alleles from 20 obligate carriers and 3 affected individuals. Eighteen alleles were represented by 12 previously identified mutations, 7 that were newly identified, and 1 that remains unidentified. We then investigated 46 enzyme-defined carrier alleles: 19 were pseudodeficiency alleles, and five mutations accounted for 15 other alleles. An eighth new mutation was detected among enzyme-defined carriers. Eleven alleles remain unidentified, despite the testing for 23 alleles. Some may represent false positives for the enzyme test. Our results indicate that predominant mutations, other than the two pseudodeficiency alleles (739C-->T and 745C-->T) and one disease allele (IVS9+1G-->A), do not occur in the general population. This suggests that it is not possible to define a collection of mutations that could identify an overwhelming majority of the alleles in non-Jews who may require Tay-Sachs carrier screening. We conclude that determination of carrier status by DNA analysis alone is inefficient because of the large proportion of rare alleles. Notwithstanding the possibility of false positives inherent to enzyme screening, this method remains an essential component of carrier screening in non-Jews. DNA screening can be best used as an adjunct to enzyme testing to exclude known HEXA pseudodeficiency alleles, the IVS9+1G-->A disease allele, and other mutations relevant to the subject's genetic heritage.

Clinical and biochemical spectrum of patients with RSH/Smith-Lemli-Opitz syndrome and abnormal cholesterol metabolism.

RSH/Smith-Lemli-Opitz (RSH/SLO) syndrome is an autosomal recessive malformation syndrome recently shown to be associated with a severe deficiency of cholesterol biosynthesis and markedly elevated plasma and tissue levels of 7-dehydrocholesterol (7-DHC), the immediate precursor of cholesterol in the Kandutsch-Russell biosynthetic pathway. Because these biochemical abnormalities permit a reassessment of RSH/SLO on biochemical criteria rather than less specific physical criteria, we review here the clinical and biochemical characteristics of our first 80 patients with abnormally increased levels of 7-DHC. The study population included 68 index patients and 12 additional relatives identified by quantification of 7-DHC and cholesterol in plasma, amniotic fluid, or cultured fibroblasts, lymphoblasts, or amniocytes. As demonstrated in other clinical syndromes when redefined biochemically, we have found a wider range of clinical expression of RSH/SLO than previously recognized. These newly recognized atypical RSH/SLO patients included several with no malformations other than syndactyly of the toes and, at the other extreme, patients with frank holoprosencephaly or multiple visceral anomalies who died in utero. Syndactyly of toes 2 and 3 was the most common malformation, occurring in all but one of 80 patients. The best biochemical predictor of clinical severity was the plasma cholesterol level, which decreased with increasing clinical severity. However, at least 10% of patients, including one newborn infant, had normal cholesterol levels at the time of diagnosis and would have been missed without specific quantification of 7-DHC. Not unexpectedly, several patients carrying a clinical diagnosis of RSH/SLO were found to have normal levels of all plasma sterols and apparently normal cholesterol biosynthesis in cultured cells. A comparison of the frequency of anomalies in our biochemically identified patients with similar data from previously reported clinical series suggests that up to 25% of reports of RSH/SLO in the literature may describe genetic conditions other than RSH/SLO with 7-DHC-emia.

Heterozygosity for Tay-Sachs and Sandhoff diseases among Massachusetts residents with French Canadian background.

OBJECTIVES: The frequency of Tay-Sachs disease (TSD) heterozygosity is increased among French Canadians in eastern Quebec. A large proportion of the New England population has French Canadian heritage; thus, it is important to determine if they too are at increased risk for TSD heterozygosity. This prospective study was designed to assess the TSD heterozygote frequency among people with French Canadian background living in Massachusetts. A simultaneous screen for heterozygosity for Sandhoff disease, a related genetic disorder, was also undertaken. METHODS: 1260 non-pregnant subjects of French Canadian background were included in the study. beta hexosaminidase activity was measured in blood samples, and results were evaluated for TSD and Sandhoff disease heterozygosity. Samples from the TSD heterozygotes were also subjected to mutation analysis. RESULTS: Of the 1260 samples studied, 22 (1 in 57; CI 1 in 41, 1 in 98) were identified as TSD heterozygotes by enzymatic analyses and 11 subjects (1 in 114; CI 1 in 72, 1 in 280) were identified as Sandhoff disease heterozygotes. Three of the 22 TSD heterozygotes were found to have benign pseudodeficiency mutations, resulting in a maximum TSD heterozygote frequency of 19 in 1260 (1 in 66; CI 1 in 46, 1 in 120). Together, these data provide a maximum frequency of heterozygosity for TSD or Sandhoff disease of 30 in 1260 (1 in 42; CI 1 in 31, 1 in 64) in this population. CONCLUSIONS: Simultaneous screening for TSD and Sandhoff disease heterozygosity by assay of beta hexosaminidases A and B activities provides a possible method for use with subjects of French Canadian background. The relevance of some of the novel mutations identified in this group needs further study. However, the comparatively high combined frequency of TSD and Sandhoff disease heterozygosity indicates a need for discussion regarding the appropriateness of carrier testing for these disorders for persons of French Canadian background in Massachusetts.

Heterozygote screening for Tay-Sachs disease: past successes and future challenges.

Tay-Sachs disease (TSD) is an autosomal recessive, neurodegenerative disorder caused by a deficiency of beta-hexosaminidase A activity. Mass screening for TSD heterozygotes has been routine in the Ashkenazi Jewish population since the early 1970s. Recent advances in the molecular genetics and epidemiology of TSD require a reevaluation of heterozygote screening practices. The use of DNA-based analyses for a panel of common mutations detects about 98% of TSD mutations found in the Ashkenazi Jews and about 50% of TSD mutations found in the general non-Jewish population; enzyme-based analysis has nearly 100% sensitivity for all populations. We recommend 1) that members of several ethnic groups and persons with a family history consistent with TSD be offered testing for TSD heterozygosity and 2) that assays of enzyme activity be used as the primary screening tool, with mutation analysis used as an adjunct tool in certain cases.

Unusual thermolability properties of beta-hexosaminidase: studies of enzyme from cultured cells and clinical implications.

Tay-Sachs disease (TSD) is a neurodegenerative genetic disorder caused by a deficiency of beta-hexosaminidase A (Hex A) activity. To diagnose TSD and to screen for TSD heterozygosity, laboratories use an assay that exploits the differential thermolability of the major beta-hexosaminidase isoenzymes, Hex A and Hex B. At 50-52 degrees C Hex A is labile, and Hex B is stable. We previously noted that the stability of leukocyte Hex B at 52 degrees C varied significantly, depending on the sample concentration in the incubation mixture. We have now examined this phenomenon in enzyme from cultured cells used for prenatal and postnatal diagnostic testing. We found that fibroblast Hex A and Hex B behave similarly to the leukocyte isoenzymes. In control and TSD fibroblasts there was a linear correlation between Hex B thermostability and sample concentration; at lower sample concentrations Hex B was less stable than at higher concentrations. Dialysis of the samples prior to heat treatment did not change the thermostability properties of Hex B, indicating that the change in stability is not due to a soluble low molecular weight substance. Cultured amniotic fluid cell and chorionic villus cell Hex B had a similar, but less pronounced, instability at low sample concentrations. Therefore, the unusual thermolability properties of Hex B, first detected for leukocyte Hex B, were noted in multiple tissues. Based on these data, we suggest that the concentration of cell extract be stringently controlled when the heat-inactivation method is used for the pre- or postnatal diagnosis of TSD, and that supplementation with non-thermolability-based beta-hexosaminidase assays should be employed as needed.

Heterozygosity for Tay-Sachs disease in non-Jewish Americans with ancestry from Ireland or Great Britain.

We performed a genetic epidemiological analysis of American non-Jewish people with ancestry from Ireland or Great Britain with regard to heterozgosity for Tay-Sachs disease (TSD). This study was prompted by a recent report that the frequency of heterozygosity for TSD among Irish Americans was 1 in 8, a frequency much higher than that recognised for any other population group. We identified 19 of 576 (3.3%) people of Irish background as TSD heterozygotes by the standard thermolability assay for beta-hexosaminidase A (Hex A) activity. Three of 289 people of non-Irish British Isles background (1%) were also identified as heterozygotes by biochemical testing. Specimens from the biochemically identified Irish heterozygotes were analysed for seven different Hex A alpha subunit gene mutations; three (15.8%) had a lethal +1 IVS-9 G to A mutation, previously noted to be a common mutation among TSD heterozygotes of Irish ancestry. Eight of 19 (42.1%) had one of two benign or pseudodeficiency mutations, and no mutation was found in 42.1% of the heterozygotes analysed. These data indicate that non-Jewish Americans with Irish background have a significantly increased frequency of heterozygosity at the Hex A alpha subunit gene locus, but that approximately 42% of the biochemically ascertained heterozygotes have clinically benign mutations. A pseudodeficiency mutation was identified in one of the three TSD heterozygotes of non-Irish British Isles background; no mutations were found in the other two. The data allow for a frequency estimate of deleterious alleles for TSD among Irish Americans of 1 in 192 to 1 in 52. Non-Jewish Americans with ancestry from Great Britain have a minimal, if any, increase in rate of heterozygosity at the TSD gene locus relative to the general population.

Plasma hyaluronidase activity in mucolipidoses II and III: marked differences from other lysosomal enzymes.

A nearly pathognomonic finding of the lysosomal storage disorders mucolipidoses II and III is the marked increase of plasma lysosomal enzyme activities. The genetic lesion in ML II and III causes defective function of the enzyme UDP-GlcNAc:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase. Defective function of this enzyme results in deficient phosphorylation of lysosomal enzyme asparagine-linked oligosaccharides and a consequent misrouting of many newly synthesized lysosomal enzymes. These enzymes are secreted from cells instead of being targeted to lysosomes, with resultant marked elevations of multiple lysosomal enzyme activities in plasma. We report here that plasma hyaluronidase activity, an endoglycosidase of presumably lysosomal origin, is not increased in the plasma from individuals with mucolipidoses II and III, unlike most lysosomal enzymes. Our data suggest the possibility that hyaluronidase is not targeted to lysosomes by a lysosomal enzyme phosphosmannosyl recognition mechanism. Alternatively, hyaluronidase activity may not be present in the cell type(s) responsible for the lysosomal enzyme hypersecretion in mucolipidoses II and III which, along with its deficiency in fibroblasts and leukocytes, would constitute an unusual tissue distribution of activity for a soluble lysosomal enzyme.

Urinary bile acids and peroxisomal bifunctional enzyme deficiency.

The biosynthesis of normal bile acids involves beta-oxidation of the 8-carbon side-chain of cholesterol, in addition to numerous modifications of the sterol nucleus. Because beta-oxidation of the sterol side-chain has been localized to the peroxisome, bile acid analysis has been suggested to be useful in the diagnostic evaluation of individuals suspected of having peroxisomal disorders. Although data from subjects with generalized peroxisomal disorders support this, few data exist regarding the bile acids in individuals having single peroxisomal beta-oxidation enzyme disorders. In this study, we analyzed the urinary bile acids from 12 patients with peroxisomal bifunctional protein deficiency using continuous flow fast atom bombardment mass spectrometry. All 12 patients had abnormal spectra, although their ion profiles and rank order of intensity of ions varied considerably. Ten of 12 individuals had abnormal spectra with presence of taurine-conjugated tetrahydroxycholestenoates, allowing a definite diagnosis of a peroxisomal beta-oxidation defect and a presumptive diagnosis of bifunctional protein deficiency; the other two cases were nondiagnostically abnormal. The strengths and limitations of urinary bile acid analysis for the diagnosis of peroxisomal beta-oxidation disorders are discussed.