X-chromosome inactivation is mostly random in placental tissues of female monozygotic twins and triplets.

Patterns of X-chromosome inactivation in chorion, amnion, and cord from 79 pairs of twins were examined. Seven sets of triplets were included in the analysis, both as twin pairs and triplets. Twins were stratified as dizygotic (DZ), monozygotic (MZ), monochorionic, and dichorionic and were selected for birth weight discordance, discordance for congenital anomalies, twin-twin transfusion syndrome, and various patterns of vascular anastomosis. X-inactivation was predominantly symmetric. Chorion was the most likely tissue to show asymmetric X-inactivation and was found most frequently in MZ dichorionic twins. There was no correlation of X-inactivation pattern with the selected clinical criteria. This study does not confirm that asymmetric X-inactivation in embryonic tissues is a common phenomenon in female twins, including monozygotic twins.

Zygosity and placental anatomy in 15 consecutive sets of spontaneously conceived triplets.

Most triplets are trizygotic because they result from assisted reproduction. Prognosis is generally good. We analyzed 15 sets of triplets who were conceived spontaneously. Six sets were monozygotic, 7 were dizygotic, and only 2 sets were trizygotic. Considered as 45 twin pairs, 25 pairs (56%) were monozygotic. Twenty percent of these twins died as a result of twin-twin transfusion. Spontaneously conceived triplets have high risks compared with those resulting from assisted reproduction. These risks result from a high proportion of monozygotic embryos, many of whom have monochorionic placentas with vascular anastomoses, causing twin-to-twin transfusion.

Some perinatal characteristics of monozygotic twins who are dichorionic.

Zygosity testing of all multiple births allowed the identification of a subgroup of 42 monozygotic twin pairs who have dichorionic placentas, fused and separate. Perinatal outcomes of this group were compared with 110 pairs of monochorionic monozygotic twins and 148 pairs of dizygotic twins. Dichorionic monozygotic twins had the lowest incidence of preterm birth, perinatal mortality, and birth weight discordance. There was an excess of like-sexed over unlike-sexed pairs among the dizygotic twins.

Mirror-image dental fusion and discordance in monozygotic twins.

A pair of monozygotic twins had similar but not identical dental anomalies. One twin had fusion of deciduous mandibular lateral incisor and canine on the left, with normal dentition on the right; the co-twin had right mandibular incisor/canine fusion, with aplasia of the lateral incisor on the left. These findings are discussed in the context of the related phenomena of situs inversus, mirror-imaging in twins, and gradients of severity of anomalies in the four copies of the mandibular developmental dental field.

Twin zygosity testing for medical purposes.

After being poisoned by eating the mushroom species Cortinarius speciosissimus, a twin developed interstitial nephritis with acute renal failure. He received a renal transplant from his living twin brother, who was presumed dizygotic on phenotypic grounds. Fifteen years later, the twins were zygosity tested by DNA "fingerprint analysis" and found to be monozygotic, despite important phenotypic discordances. The recipient has discontinued immunosuppression therapy and remains well after 9 months. We suggest that, for medical and other reasons, zygosity should be determined at birth on all like-sexed twins.

Two pairs of male monozygotic twins discordant for Wiedemann-Beckwith syndrome.

Wiedemann-Beckwith syndrome (WBS) is a congenital anomaly syndrome which classically consists of exomphalos, macroglossia, and gigantism. The syndrome is also associated with a variety of minor anomalies and affected individuals have an increased risk of developing rare embryonal cell tumors. To date, 15 monozygotic (MZ) twin pairs have been reported of which 13 are discordant for WBS. All except one pair of the discordant WBS twin pairs have been female. We report two pairs of male MZ twins, each discordant for WBS.

Normal reference ranges for biochemical substances relating to renal, hepatic, and bone function in fetal and maternal plasma throughout pregnancy.

Normal reference ranges for sodium, potassium, urea, creatinine, calcium, phosphate, total protein, albumin, bilirubin, alkaline phosphatase, and aspartate transaminase were determined from 344 fetal and maternal plasma samples between 15 and 38 weeks' gestation. Pure fetal blood was obtained by fetoscopy in the second trimester and in the third trimester by umbilical cord puncture at delivery. All biochemical substances were measured by continuous flow (SMAC, Technicon) except albumin, which was measured by turbidimetry (CobasBio, Roche). The resulting data were analysed on an AMDAHL 470A computer and reference ranges covering 2.5 to 97.5 percentiles were defined. Analysis of variance was performed to examine the overall effect of gestational age on the analytes measured and on the changes in the fetal compartment relative to the mothers'. A paired t test was performed to examine how these biochemical substances in fetal plasma related to maternal plasma from the same pregnancy.

Laboratory screening for genetic disorders and birth defects.

Screening for inherited disease is a preventative health measure that started in the 1960s with the development of programs for the detection of PKU in newborns and that has had a major impact on reducing the burden of disease. Developments in technology have led to the availability of large scale testing for an increasing number of both acquired and genetic disorders. Laboratory testing is only one facet of a screening program and consideration should be given to availability of testing to all individuals, education regarding the program, effectiveness of treatment, long-term benefits both for individuals and society, ethical issues, and cost benefits. In this review, newborn, prenatal, and heterozygote screening are discussed.

Biochemical investigation of a child with molybdenum cofactor deficiency.

A girl aged eight months, who presented with developmental delay and dislocated optic lenses, was diagnosed as having combined sulfite oxidase and xanthine dehydrogenase deficiencies consistent with molybdenum cofactor deficiency. The diagnosis was confirmed by demonstrating the absence in urine of urothione, a molybdenum cofactor metabolite. Prenatal diagnosis excluded the disease in the mother's second pregnancy. A summary of an in vitro study of molybdenum cofactor synthesis in the patient is given.

Serum free thyroxine and free triiodothyronine concentrations in healthy fullterm, preterm and sick preterm neonates.

There are few data available on free thyroid hormone concentrations in the early neonatal period. With the widespread application of screening procedures for detecting congenital hypothyroidism there is a need for reference ranges in neonates. In this study we have evaluated thyroid function in healthy fullterm and preterm neonates, and sick neonates all within one to 10 days postnatal age. Our data indicates that free thyroxine but not free triiodothyronine is higher in fullterm neonates than the adult reference range and that both free thyroid hormone concentrations are reduced in healthy and sick preterm neonates as compared to fullterm neonates. Assessment of thyroid function in the early neonatal period needs to take into account these changes particularly in preterm and sick preterm neonates.

A case of aplasia cutis congenita in dizygotic twins.

We report a newborn infant with extensive aplasia cutis congenita of the flanks and thighs, associated with a co-twin fetus papyraceus. DNA restriction fragment polymorphism analysis of the twins proved dizygosity. The association of these two conditions in twins is reviewed.

Development of a clinical assay for detection of GAA mutations and characterization of the GAA mutation spectrum in a Canadian cohort of individuals with glycogen storage disease, type II.

Glycogen storage disease, type II (GSDII; Pompe disease; acid maltase deficiency) is an autosomal recessive disease caused by mutations of the GAA gene that lead to deficient acid alpha-glucosidase enzyme activity and accumulation of lysosomal glycogen. Although measurement of acid alpha-glucosidase enzyme activity in fibroblasts remains the gold standard for the diagnosis of GSDII, analysis of the GAA gene allows confirmation of clinical or biochemical diagnoses and permits predictive and prenatal testing of individuals at risk of developing GSDII. We have developed a clinical molecular test for the detection of GAA mutations based on cycle sequencing of the complete coding region. GAA exons 2-20 are amplified in six independent PCR using intronic primers. The resulting products were purified and sequenced. Preliminary studies using this protocol were conducted with DNA from 21 GSDII-affected individuals from five centers across Canada. In total, 41 of 42 mutations were detected (96.7% detection rate). Mutations spanned intron 1 through exon 19 and included nine novel mutations. Haplotype analysis of recurrent mutations further suggested that three of these mutations are likely to have occurred independently at least twice. Additionally, we report the identification of the c.-32-13T>G GAA mutation in an individual with infantile variant GSDII, despite reports of this mutation being associated almost exclusively with late-onset forms of the disease. The development of a clinical molecular test provides an important tool for the management and counseling of families and individuals with GSDII, and has provided useful information about the GAA mutation spectrum in Canada.

Population affinities of Neolithic Siberians: a snapshot from prehistoric Lake Baikal.

Archaeological evidence supports the inhabitation of the Lake Baikal region since the Paleolithic. Both metric and nonmetric osteological studies suggest that Neolithic Cis-Baikal populations are the ancestors of contemporary inhabitants of the region. To date, ancient DNA data have not been used to corroborate this biological continuity hypothesis. This study presents a temporal snapshot of the Cis-Baikal Neolithic by examining mtDNA diversity in two cemetery populations situated on the Angara River downstream of Lake Baikal. The 800 years separating the use of the two cemeteries is thought to represent a biocultural hiatus in the Cis-Baikal region, one that ended when a new group migrated into the area. To assess the likelihood that genetic continuity exists between these two Neolithic groups, we examined both mtDNA coding region and hypervariable region I (HVI) polymorphisms from skeletal remains excavated from both cemeteries (Lokomotiv and Ust'-Ida). The mtDNA haplogroup distributions of the two cemetery populations differ significantly, suggesting that they were biologically distinct groups. When the biological distance between these Neolithic groups is compared with modern Siberian and other East Eurasian groups, the posthiatus group (Serovo-Glazkovo) generally aligns with contemporary Siberians, while the prehiatus (Kitoi) individuals are significantly different from all but modern Kets and Shorians living in the Yenisey and Ob River basins to the west of Lake Baikal. These results suggest that the Lake Baikal region experienced a significant depopulation event during the sixth millennium BP, and was reoccupied by a new immigrant population some 800 years later.

Alpha 1 antitrypsin deficiency due to Pi null: clinical presentation and evidence for molecular heterogeneity.

The proteinase inhibitor null (Pi-) allele is a rare cause of alpha 1 antitrypsin (AAT) deficiency. In three families, all the subjects with AAT deficiency due to PiZ- presented in early childhood with recurrent chest infections and wheezing presumably related to passive smoking. In Pi- the AAT gene is present and there is no evidence for a gene deletion. In one family a restriction fragment length polymorphism (RFLP) detected with the enzyme XbaI segregates with the Pi- allele. In a family where a consanguineous marriage occurred, the XbaI polymorphism segregates with the normal M1 allele rather than Pi-, suggesting that Pi- may have originated from M1. In contrast, a third family and 20 normal unrelated subjects do not show the RFLP.

Who gets missed: coverage in a provincial newborn screening program for metabolic disease.

OBJECTIVE: To determine coverage of the newborn screening program (NSP) for metabolic disease in Alberta, Canada, and to determine reasons for not being screened. STUDY DESIGN: Coverage was estimated by deterministic matching of live birth registration data with newborn screening data for the year 1992. Demographic characteristics of not-matched infants were compared with good-match infants using logistic regression. RESULTS: For 42 392 live births, there were 41 553 screening records, of which 40 593 infants were very good matches to NSP records. Another 960 were possible matches. A total of 839 infants were not matched at all, and coverage was estimated at 98.0%. Determinants of infant not-matched status were death in week 1 (adjusted odds ratio [OR]: 383); birth weight of <1500 g (adjusted OR: 18.9) or between 1500 and 2500 g (adjusted OR: 3.2); having a mother who was single (adjusted OR: 2.7) or formerly married (adjusted OR: 12.9); or being born out of hospital (OR: 19. 2). The calculated 98% coverage is close to an estimate of 98.3% made by the NSP comparing total births with initial screenings. CONCLUSION: The matched data give insight as to who was missed and point to the need for closer attention for infants at greater risk of not being screened for metabolic disease.

Who gets lost: follow-up of suspect results in a newborn screening program

Objective. To determine reasons for and adequacy of follow-up testing of suspect results of metabolic screening in infants born in Alberta in 1992. Study Design. Of 42 392 live births, 41 553 infants were deterministically matched using birth registry data. Infants requiring repeat analyses were determined from notes made on the screening report. Characteristics of infants needing repeat screening, and obtaining a repeat screen results, were determined by logistic regression using variables from the birth registry and the screening record. Results. A total of 1375 infants required repeat screening. Infants with unsatisfactory samples were more likely to be born in a smaller community, of low birth weight, and to have the sample obtained after 7 days of age. Infants with biologically suspect results were more likely to be of low birth weight, to die in week 1 of life, and to be born in a large hospital. Repeat analyses were found for 663 infants. Boys, infants from smaller communities, and low birth weight infants were more likely to have the required repeat screening. Infants of single mothers were less likely to undergo repeat screening. Conclusions. The results of this study demonstrate the need for a clear, time-oriented protocol of follow-up of newborn metabolic screening results.

Molecular characterisation of two alpha-1-antitrypsin deficiency variants: proteinase inhibitor (Pi) Null(Newport) (Gly115----Ser) and (Pi) Z Wrexham (Ser-19----Leu).

Two single point mutations in the alpha-1-antitrypsin gene, resulting in AAT deficiency, have been characterised in heterozygotes by DNA amplification and direct sequencing. The mutations result in amino acid substitutions, Gly115----Ser and Ser-19----Leu, in the leader sequence, respectively, and have been designated Pi Null(Newport) and Pi Z Wrexham. In the two families studied the mutations occur on chromosomes which also carry the common mutation causing Z deficiency. Individuals with such a deficiency are, therefore, compound heterozygotes. It is not known if these particular mutations would only cause a mild form of AAT deficiency in the absence of the Z mutation as they do not appear to cause predictable folding abnormalities. They do, however, result in severe deficiency when the Z mutation occurs in the same gene.