Medium chain acyl-CoA dehydrogenase deficiency human genome epidemiology review.

Medium chain acyl-CoA dehydrogenase (MCAD) is a tetrameric flavoprotein essential for the beta-oxidation of medium chain fatty acids. MCAD deficiency (MCADD) is an inherited error of fatty acid metabolism. The gene for MCAD is located on chromosome one (1p31). One variant of the MCAD gene, G985A, a point mutation causing a change from lysine to glutamate at position 304 (K304E) in the mature MCAD protein, has been found in 90% of the alleles in MCADD patients identified retrospectively. There is a high frequency of MCADD among people of Northern European descent, which is believed to be due to a founder effect. MCADD is inherited in an autosomal recessive manner. Of patients clinically diagnosed with MCADD, 81% who have been identified retrospectively are homozygous for K304E, and 18% are compound heterozygotes for K304E. Clinical data on the probability of clinical disease indicates that MCADD patients are at risk for the following outcomes: hypoglycemia, vomiting, lethargy, encephalopathy, respiratory arrest, hepatomegaly, seizures, apnea, cardiac arrest, coma, and sudden and unexpected death. Long-term outcomes include developmental and behavioral disability, chronic muscle weakness, failure to thrive, cerebral palsy, and attention deficit disorder (ADD). Differences in clinical disease specific to allelic variants have not been documented. Factors that may increase risk for disease onset or modify disease severity are age when the first episode occurred, fasting, and presence of infection. Acute attacks must be treated immediately with appropriate intravenous doses of glucose. For those diagnosed, long-term management of the disease includes preventing stress caused by fasting and maintaining a high-carbohydrate, reduced-fat diet, and carnitine supplementation. Hospitalization costs attributable to morbidity and mortality from MCADD are unknown; MCADD is not a diagnosis in the International Classification of Disease, 10th Revision (ICD-10) codebook. Furthermore, the penetrance of the MCAD genotypes is unknown; there appears to be a substantial number of asymptomatic MCADD individuals and some uncertainty regarding which individuals will manifest symptoms and which individuals will remain asymptomatic. Several technologies are available to detect MCADD. Diagnostic technologies include DNA-based tests for K304E mutations using the polymerase chain reaction (PCR), and the detection of abnormal metabolites in urine. Screening technologies include tandem mass spectrometry (MS/MS), which detects abnormal metabolites mostly in blood. State programs are beginning to offer screening in newborns for MCADD using MS/MS. In addition, a private company currently offers voluntary supplemental newborn screening for MCADD to birthing centers.

Monitoring the prevalence of congenital hypothyroidism for 20 years near the Savannah River site.

OBJECTIVES: The main objectives were to describe the epidemiology of primary congenital hypothyroidism (CH) in Georgia during the past 20 years and specifically to determine whether there was a significant increase in CH prevalence proximal to the Savannah River Site (SRS), a nuclear plant. METHODS: Data were derived from the Georgia Newborn Screening Program. Frequencies were determined for race, sex, birth weight and birth month. Seasonality effects were investigated and the prevalence was determined and mapped by health district. RESULTS: The majority of the CH cases were female, white and of average birth weight. The sex ratio varied by race/ethnicity. There was not a statistically significant increase in the prevalence in the eastern districts that were in close proximity to the SRS. CONCLUSIONS: Although there were differences in the prevalence between health districts, we found no increased prevalence of CH in those health districts proximal to the SRS.

Lymphedema as a postulated cause of cutis verticis gyrata in Turner syndrome.

Unusual skin lesions were present at birth in four infants with Turner syndrome. The skin changes in these patients appear to have resulted either from in utero entrapment or pinching of edematous skin or from redundant skin remaining after in utero resolution of lymphedema. Distention by lymphedema is thought to cause several of the phenotypic characteristics seen in patients with Turner syndrome, including nuchal webbing and nail changes. In three of these patients the clinical appearance of the skin changes was similar to cutis verticis gyrata, marked by fixed thickened plaques in folds.

Defective urinary carnitine transport in heterozygotes for primary carnitine deficiency.

PURPOSE: Primary carnitine deficiency is an autosomal recessive disorder caused by defective carnitine transport and manifests as nonketotic hypoglycemia or skeletal or heart myopathy. METHODS: To define the mechanisms producing partially reduced plasma carnitine levels in the parents of affected patients, we examined carnitine transport in vivo and in the fibroblasts of a new patient and his heterozygous parents. RESULTS: Kinetic analysis of carnitine transport in fibroblasts revealed an absence of saturable carnitine transport in the proband's cells and a partially impaired carnitine transport in fibroblasts from both parents, whose cells retained normal Km values toward carnitine (6-9 microM) but reduced Vmax. At steady state, normal fibroblasts accumulated carnitine to a concentration that was up to 80 times the extracellular value (0.5 microM). By contrast, cells from the proband had minimal carnitine accumulation, and cells from both parents had intermediate values of carnitine accumulation. Plasma carnitine levels were slightly below normal in both heterozygous, yet clinically normal, parents and in the paternal grandfather and the maternal grandmother. To define the mechanism producing partially decreased carnitine levels, we studied urinary carnitine losses in heterozygous parents compared with controls. Urinary losses increased linearly (P < 0.05) with plasma carnitine levels in normal controls. When urinary carnitine losses were normalized to plasma carnitine levels, a significant difference was observed between controls and heterozygous individuals (P < 0.01). CONCLUSIONS: These results indicate that fibroblasts from heterozygotes for primary carnitine deficiency have a decreased capacity to accumulate carnitine and that heterozygotes have increased urinary losses, which may contribute to their reduced plasma carnitine levels.

An evaluation of the use of dried blood spots from newborn screening for monitoring the prevalence of cocaine use among childbearing women.

A collaborative March of Dimes study was designed to examine the utility of dried blood spot (DBS) materials routinely collected from newborns as a source for monitoring cocaine exposure and to assess the prevalence of cocaine use among childbearing women in Georgia. We used a modified urinary radioimmunoassay (RIA) to anonymously detect the cocaine metabolite benzoylecgonine (BE) in DBSs. Extensive efforts were undertaken to assure absolute nonlinkage of BE data to any individual. The positive results found by RIA were confirmed by a mass spectrometry (MS) method specifically developed to detect BE in DBSs. BE was measured in 23,141 DBSs collected during 2 months of routine newborn screening in Georgia. A good correlation was observed for RIA results versus MS results (r2 = 0.97). The estimated minimal statewide BE prevalence was 4.8 per 1000 childbearing women. We demonstrated that immunoassay testing for cocaine without confirmatory testing can yield falsely elevated prevalence rates. When proper confirmatory testing is done, DBSs are a valuable source for population-based monitoring of substance abuse among childbearing women.

Population study of congenital hypothyroidism and associated birth defects, Atlanta, 1979-1992.

Very little data are available from population-based studies on congenital hypothyroidism (CH) epidemiology and patterns of associated birth defects. By linking data from two population-based registries, we describe the epidemiology of CH and associated defects in Atlanta from 1979-1992. Cases included all infants with CH born from 1979-1992 to mothers residing in the metropolitan Atlanta area at the time of birth. We ascertained CH cases by reviewing newborn screening records and records of the Metropolitan Atlanta Congenital Defects Program (MACDP), a population-based registry of all serious birth defects diagnosed during a child's first year of life. We linked CH cases with MACDP records to ascertain the presence of serious birth defects among infants with CH. Of 97 infants identified with CH through newborn screening and/or MACDP (1:5,000 live births), 87 had primary CH and 10 had secondary. The rate of primary CH was higher among non-hispanic whites than among blacks (1:4,400 vs. 1:10,000) and among females compared with males (1:4,000 vs. 1:7,700). Among infants with primary CH, 77 had isolated CH, 3 had Down syndrome, and 7 had unrelated major structural defects. Based on Atlanta population rates of Down syndrome and major structural anomalies, we infer i) infants with Down syndrome have a 35-fold increased risk for primary CH compared with infants in the general population (P < .0001); ii) infants with primary CH have a 2.2-fold increased risk for major structural anomalies (P < .05). Because this is the first population study of CH in the United States in which data from two population-based registries were linked, the epidemiologic patterns and associated defects are more representative than those found in studies based on newborn screening records only.

Analysis of benzoylecgonine in dried blood spots by liquid chromatography--atmospheric pressure chemical ionization tandem mass spectrometry.

Residual samples from blood spots (i.e., whole blood spotted onto filter paper) are a useful source for epidemiological screening studies involving newborns. However, the small volume of blood available from residual blood spots complicates the assay. A method for analyzing benzoylecgonine (BZE; the primary metabolite of cocaine) in blood spots, in which the blood spot is eluted with aqueous ammonium acetate-methanol containing N-methyl trideuterated-BZE as an internal standard, followed by high-performance liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry using multiple reaction monitoring, has been developed. This approach provides a rapid, direct, sensitive (limit of detection, approximately 2 ng/mL, based on a 12-microL sample size), and highly specific means of determining BZE concentrations in blood spots. We have applied this method for confirmatory analyses in a large epidemiological study of the prevalence of cocaine use during late pregnancy.

Unique mosaicism of tetraploidy and trisomy 8: clinical, cytogenetic, and molecular findings in a live-born infant.

We report on a live-born infant with mosaicism of tetraploidy and trisomy 8 who had craniofacial abnormalities, cardiac and genitourinary defects, agenesis of the corpus callosum, and anomalies of limbs. The infant died at age 14 weeks. Molecular studies were done on peripheral blood lymphocytes and cultured amniocytes to determine the origin of the cytogenetic abnormalities. On the basis of the results, we describe a possible mechanism to explain these abnormalities. To our knowledge, this infant represents the first reported case of mosaic trisomy 8 with a tetraploid cell line.

Impact of prenatal diagnosis on the birth prevalence of neural tube defects, Atlanta, 1990-1991.

OBJECTIVE: To determine the impact of prenatal diagnosis on the birth prevalence of neural tube defects (NTDs) in Atlanta during 1990 through 1991. METHODS: Live-born and stillborn infants with NTDs who were at least 20 weeks' gestation were ascertained by the Metropolitan Atlanta Congenital Defects Program (MACDP), a population-based birth defects registry. Prenatally diagnosed NTD-affected pregnancies were ascertained from the four perinatal centers and the three genetic laboratories operating in Atlanta during 1990 through 1991. Fetal death certificates were also reviewed for potential cases. RESULTS: During 1990 through 1991, MACDP ascertained 59 NTD cases, for a birth prevalence of 0.77/1000 live births. During this period, an additional 28 NTD-affected pregnancies were detected prenatally and terminated before 20 weeks' gestation. The adjusted NTD rate during 1990 through 1991, which includes prenatally diagnosed cases, was 1.13/1000 live births. CONCLUSIONS: Prenatal diagnosis is making a substantial impact on the birth prevalence of NTDs in Atlanta. However, since NTD rates in Atlanta were 2 to 2.5 per 1000 live births in 1970, prenatal diagnosis and termination of pregnancy does not completely account for the declining rate of NTDs.

Galactosemia: a strategy to identify new biochemical phenotypes and molecular genotypes.

We describe a stratagem for identifying new mutations in the galactose-1-phosphate uridyl transferase (GALT) gene. GALT enzyme activity and isoforms were defined in erythrocytes from probands and their first-degree relatives. If the biochemical phenotypes segregated in an autosomal recessive pattern, we screened for common mutations by using multiplex PCR and restriction endonuclease digestions. If common mutant alleles were not present, the 11 exons of the GALT gene were amplified by PCR, and variations from the normal nucleotide sequences were identified by SSCP. The suspected region(s) was then analyzed by direct DNA sequencing. We identified 86 mutant GALT alleles that reduced erythrocyte GALT activity. Seventy-five of these GALT genomes had abnormal SSCP patterns, of which 41 were sequenced, yielding 12 new and 21 previously reported, rare mutations. Among the novel group of 12 new mutations, an unusual biochemical phenotype was found in a family whose newborn proband has classical galactosemia. He had inherited two mutations in cis (N314D-E203K) from his father, whose GALT activity was near normal, and an additional GALT mutation in the splice-acceptor site of intron C (IVSC) from his mother. The substitution of a positively charged E203K mutation created a unique isoform-banding pattern. An asymptomatic sister's GALT genes carries three mutations (E203K-N314D/N314D) with eight distinct isoform bands. Surprisingly, her erythrocytes have normal GALT activity. We conclude that the synergism of pedigree, biochemical, SSCP, and direct GALT gene analyses is an efficient protocol for identifying new mutations and speculate that E203K and N314D codon changes produce intraallelic complementation when in cis.

Corneal opacities in spondyloepiphyseal dysplasia tarda.

Spondyloepiphyseal dysplasia tarda is an inherited skeletal dysplasia involving the spine and epiphyses of long bones with onset in childhood, giving rise to disproportionate short stature and degenerative spine and hip disease. Associated ocular disease is not commonly recognized. We report a patient with spondyloepiphyseal dysplasia tarda and a unique pattern of corneal opacities. Bilateral, irregularly shaped, nodular, deeply posterior opacities confined to the peripheral cornea were noted in this patient. A central stromal granularity was also seen. Minimal visual loss was associated with these findings. An X-linked inheritance pattern is presumed but could not be confirmed.

Paternal uniparental disomy in a child with a balanced 15;15 translocation and Angelman syndrome.

Chromosome 15 (15q11-q13) abnormalities cause two distinct conditions, Angelman syndrome (AS) and Prader-Willi syndrome (PWS). We present the first case of a child with a balanced 15;15 translocation and AS in whom molecular studies were crucial in confirming a diagnosis. DNA polymorphisms demonstrated paternal uniparental disomy for chromosome 15, consistent with the diagnosis of AS. The molecular studies also showed the patient to be homozygous at all loci for which the father was heterozygous, suggesting that the structural rearrangement was an isochromosome 15q and not a Robertsonian translocation.

Subacute necrotizing encephalopathy: oxidative phosphorylation defects and the ATPase 6 point mutation.

Subacute necrotizing encephalopathy (SNE) or Leigh's disease is associated with various defects in oxidative phosphorylation (OXPHOS). However, the relationships between these OXPHOS defects and nuclear DNA or mitochondrial DNA (mtDNA) mutations is still unclear. We evaluated three SNE pedigrees (two singleton cases and a pedigree) biochemically for OXPHOS abnormalities and genetically for four mtDNA point mutations. There was a complex I defect in all three pedigrees that was associated with a complex III defect in two individuals. An mtDNA mutation in the ATPase, subunit 6 gene (np 8993) was present in one SNE pedigree. This mutation was maternally inherited, heteroplasmic, produced marked clinical and biochemical heterogeneity between pedigree members, and varied along the maternal lineage at levels ranging from 0% to > 95% of the total mtDNAs. These mtDNA mutations were not present in the other two pedigrees. These observations emphasize the importance of screening for OXPHOS defects and mtDNA mutations in SNE cases.