Survey of the fragile X syndrome CGG repeat and the short-tandem-repeat and single-nucleotide-polymorphism haplotypes in an African American population.

Previous studies have shown that specific short-tandem-repeat (STR) and single-nucleotide-polymorphism (SNP)-based haplotypes within and among unaffected and fragile X white populations are found to be associated with specific CGG-repeat patterns. It has been hypothesized that these associations result from different mutational mechanisms, possibly influenced by the CGG structure and/or cis-acting factors. Alternatively, haplotype associations may result from the long mutational history of increasing instability. To understand the basis of the mutational process, we examined the CGG-repeat size, three flanking STR markers (DXS548-FRAXAC1-FRAXAC2), and one SNP (ATL1) spanning 150 kb around the CGG repeat in unaffected (n=637) and fragile X (n=63) African American populations and compared them with unaffected (n=721) and fragile X (n=102) white populations. Several important differences were found between the two ethnic groups. First, in contrast to that seen in the white population, no associations were observed among the African American intermediate or "predisposed" alleles (41-60 repeats). Second, two previously undescribed haplotypes accounted for the majority of the African American fragile X population. Third, a putative "protective" haplotype was not found among African Americans, whereas it was found among whites. Fourth, in contrast to that seen in whites, the SNP ATL1 was in linkage equilibrium among African Americans, and it did not add new information to the STR haplotypes. These data indicate that the STR- and SNP-based haplotype associations identified in whites probably reflect the mutational history of the expansion, rather than a mutational mechanism or pathway.

Characterization and clinical implications of marker chromosomes identified at prenatal diagnosis.

Eighteen fetuses with marker chromosomes were detected at diagnostic amniocentesis in our laboratory among 15 781 amniocentesis samples. Using combined approaches, conventional cytogenetics including special stain techniques and fluorescence in situ hybridization (FISH), we successfully characterized 15 of them, which assisted subsequent genetic counselling. Six marker chromosomes were of sex chromosome origin, each of which substituted a missing sex chromosome, and 12 were supernumerary marker chromosomes (SMCs). Nine of the SMCs were proven to be of autosomal origin. Of those autosomal SMCs, five originated from chromosome 15, two from chromosome 18, one from chromosome 12 and one from chromosome 1. Among 16 marker chromosomes with adequate follow-up information, 50% were benign including four sex chromosome markers and four autosomal markers. Two thirds of de novo marker chromosomes were associated with abnormal outcomes, while all inherited ones were benign regardless of their parental origin. Our study demonstrated that molecular characterization of prenatal marker chromosomes is of great significance in facilitating phenotype-genotype correlation.

An association between skewed X-chromosome inactivation and abnormal outcome in mosaic trisomy 16 confined predominantly to the placenta.

Skewed X-chromosome inactivation (XCI) is frequently found in the diploid fetal tissues of individuals with mosaic trisomy that originated from a 'trisomic zygote rescue' event. This may result from a high number of trisomic cells in the embryonic cell pool at the time of XCI, which are subsequently eliminated by selection. We hypothesize that extremely skewed XCI in these mosaic cases will be associated with a poor fetal outcome due to failure to completely eliminate the trisomy from all fetal tissues. To test this hypothesis, XCI status was evaluated in 17 cases of prenatally detected trisomy 16 mosaicism. Ten of the 15 informative cases showed extreme XCI skewing ( > or = 90% inactivation of one allele) in blood or other diploid fetal tissues compared to six of the 111 controls (p < 0.001). Among these 10 'skewed' cases, 6 showed an abnormal outcome, defined as developmental abnormalities and/or intrauterine or neonatal death. In contrast, of the 5 cases without extreme skewing, none showed abnormal outcome, although outcome information was incomplete in 1 case. An additional 6 cases analyzed, involving trisomy mosaicism for other chromosomes, showed similar results. Further studies are warranted to determine if XCI status adds useful information to the prediction of pregnancy outcome in prenatally detected mosaic trisomy.

Isolated bilateral anophthalmia in a girl with an apparently balanced de novo translocation: 46,XX,t(3;11)(q27;p11.2).

Primary anophthalmos is a heterogeneous condition. In its nonsyndromal form, it is usually considered an autosomal recessive trait. However, other causes such as chromosomal abnormalities and prenatal insults need to be considered. We report on a unique reciprocal translocation 46,XX,t(3;11)(q27;p11.2) in a baby with isolated anophthalmos. Both Chitayat et al. [1996] and Alvarez Arratia et al. [1984] have reported on cases of terminal deletion of the long arm of chromosome 3. In each case the child had multiple anomalies including microphthalmia or anophthalmia. Because our patient appears to have no other anomalies, this break point may indicate that a genetic locus for eye formation exists at chromosome site 3q27. Published 1999 Wiley-Liss, Inc.

Age-related language characteristics of children and adolescents with fragile X syndrome.

In addition to moderate-to-severe mental retardation (MR), the fragile X [fra(X)] mutation produces significant impediments in speech and language. Severe delays in speech and language have been demonstrated in both adult males and young individuals with the fra(X) mutation. Having observed longitudinal declines in IQ scores in young males with fra(X) and given the relationship between cognitive ability and language skill, we wanted to determine whether speech-language deficits in young males with fra(X) were age-related in ways comparable with those observed in cognitive deficits. We examined a small sample (n = 16) of children and adolescents, ages 6-17 years, using the Clinical Evaluation of Language Fundamental-Preschool (CELF-P). The CELF-P is used to evaluate language deficits in preschool children and assesses receptive and expressive language ability. It is standardized for children ages 3-7 years and provides age-normed standard scores. To evaluate changes in language scores, we converted raw scores into age-equivalents. Results indicate that males with fra(X) have significantly lower age equivalent scores compared with females. A cross-sectional analysis of males' age-equivalent scores reveals that a plateau is reached at approximately 48 months. Our findings suggest that, as with IQ and adaptive behavior scores, language development in young, fully mutated fra(X) individuals appears to reach a plateau as they age.

Longitudinal assessment of adaptive and maladaptive behaviors in fragile X males: growth, development, and profiles.

As young fully mutated fragile X [fra(X)] males age, cognitive levels (IQ scores) and adaptive behavior levels (DQ scores) decline. Given the variable behavioral profiles reported previously, we wondered whether changes in specific attributes of adaptive behavior are related to declines in composite adaptive behavior levels. We also examined maladaptive behavior to determine if changes are related to age. Therefore, we evaluated three areas of adaptive behavior, as well as maladaptive behavior, in 28 fully mutated fra(X) males, ages 4-14 years. To develop a profile of adaptive behavior, we analyzed nine subscale scores from the Vine-land Adaptive Behavior Scale (VABS). To assess maladaptive behavior, we graded part I of the VABS Maladaptive Behavior Scale. Subjects were sorted into three age cohorts, according to their initial test age: younger than 6 years; 6 to 9 years; older than 9 years. Results indicate that, in all age groups, the communications domain is the most severely impacted compared with either the socialization domain or daily living skills and that, in all age groups, the socialization domain is a relative strength compared with either the communications domain or daily living skills. The youngest cohort manifested significant increases in age-equivalent community living skills. Significant differences in age-equivalent scores between cohorts were observed in written language and play skills. Maladaptive behavior scores were available from cross-sectional data only. Twenty males (74%) showed significantly higher maladaptive scores than expected from other children their age. Our data analysis also revealed a moderate and significant negative correlation between maladaptive behavior levels and age (r = -0.54; P < 0.01). Curiously, adaptive and maladaptive behaviors did not correlate with each other.

Longitudinal changes in cognitive and adaptive behavior in fragile X females: a prospective multicenter analysis.

In prospective studies of young, fragile X [fra(X)] males with the full mutation, cognitive abilities (IQ scores) and adaptive behavior levels (DQ scores) declined in most subjects tested. Little is known about longitudinal changes in IQ and DQ scores in young fra(X) females, although one earlier retrospective study showed declines in IQ scores in 8 of 11 subjects. To examine fra(X) females prospectively, we tested and retested 13 females with the full mutation, age 4 to 15 years. Nine were tested and retested in North America, and four were evaluated at the Catholic University in Leuven, Belgium. Cognitive abilities of North American females were measured using the Stanford-Binet 4th Edition. Adaptive behavior levels were ascertained from the Vineland Adaptive Behavior Scales. For Belgians, test-retest scores from the Wechsler Intelligence Scales for Children-Revised were used. Subjects were subsequently separated into two age cohorts: those tested initially before age 7 years and those tested initially after age 7 years. Compared with young males with the full mutation and of the same age, females expectedly display a wider range of IQ scores. Test-retest IQ scores showed statistically significant decreases (P < 0.03). Analysis of individual test-retest scores indicate that declines in eight females were statistically significant. Adaptive behavior scores were available only for North American females. Five of nine (55%) showed significant declines in DQ. Like young males with the full mutation, all females with the full mutation attained higher adaptive behavior levels than cognitive scores, i.e., DQ > IQ.

Fragile X premutation is a significant risk factor for premature ovarian failure: the International Collaborative POF in Fragile X study--preliminary data.

The preliminary results of an international collaborative study examining premature menopause in fragile X carriers are presented. A total of 760 women from fragile X families was surveyed about their fragile X carrier status and their menstrual and reproductive histories. Among the subjects, 395 carried a premutation, 128 carried a full mutation, and 237 were noncarriers. Sixty-three (16%) of the premutation carriers had experienced menopause prior to the age of 40 compared with none of the full mutation carriers and one (0.4%) of the controls. Based on these preliminary data, there is a significant association between fragile X premutation carrier status and premature menopause.

Screening semen donors for hereditary diseases. The Fairfax cryobank experience.

OBJECTIVE: To study the carrier frequency of hereditary diseases in potential semen donors with no family history of a genetic disease. STUDY DESIGN: Carrier screening was performed on potential semen donors for chromosomal abnormalities, cystic fibrosis, alpha-1-antitrypsin deficiency, hemoglobinopathies, Tay-Sachs disease, Gaucher disease, Canavan disease, and hereditary breast and ovarian cancer (the BRCA1 185delAG mutation). The screening regimen used for each donor was dictated by his ethnic background. RESULTS: Among 361 individuals screened for chromosomal abnormalities, 1 carried an inversion, and 4 were possible mosaics. Fifteen of 407 potential donors carried cystic fibrosis, 18 of 209 carried alpha-1-antitrypsin deficiency, and 2 of 74 carried a hemoglobinopathy. No carriers of Tay-Sachs disease (56 screened), Gaucher disease (32 screened), Canavan disease (22 screened) or the BRCA1 185delAG mutation (22 screened) were found. CONCLUSION: Screening semen donors for a number of genetic diseases that are passed silently from generation to generation is warranted since family history alone cannot identify them.

Meiotic origin of trisomy in confined placental mosaicism is correlated with presence of fetal uniparental disomy, high levels of trisomy in trophoblast, and increased risk of fetal intrauterine growth restriction.

Molecular studies were performed on 101 cases of confined placental mosaicism (CPM) involving autosomal trisomy. The origin of the trisomic cell line was determined in 54 cases (from 51 pregnancies), 47 of which were also analyzed for the presence of uniparental disomy (UPD) in the disomic cell line. An additional 47 cases were analyzed for parental origin in the disomic cell line only. A somatic (postmeiotic) origin of the trisomy was observed in 22 cases and included the majority of cases with CPM for trisomy 2, 7, 8, 10, and 12. Most cases of CPM involving trisomy 9, 16, and 22 were determined to be meiotic. Fetal maternal UPD was found in 17 of 94 informative CPM cases, involving trisomy 2 (1 case), 7 (1 case), 16 (13 cases), and 22 (2 cases). The placental trisomy was of meiotic origin in all 17 cases associated with fetal UPD (P = .00005). A meiotic origin also correlated with the levels of trisomy in cultured chorionic villi samples (CVS) (P = .0002) and trophoblast (P = .00005). Abnormal pregnancy outcome (usually IUGR) correlated with meiotic origin (P = .0003), the presence of fetal UPD (P = 4 x 10(-7)), and the level of trisomy in trophoblast (P = 3 x 10(-7)) but not with the level of trisomy in CVS or term chorion. The good fit of somatic errors with the expected results could have been observed only if few true meiotic errors were misclassified by these methods as a somatic error. These data indicate that molecular determination of origin is a useful predictor of pregnancy outcome, whereas the level of trisomy observed in cultured CVS is not. In addition, UPD for some chromosomes may affect prenatal, but not postnatal, development, possibly indicating that imprinting effects for these chromosomes are confined to placental tissues.

Trisomy 7 CVS mosaicism: pregnancy outcome, placental and DNA analysis in 14 cases.

Prenatal diagnosis by chorionic villus sampling (CVS) documents placental chromosomal mosaicism in approximately 2% of viable pregnancies at 9-12 weeks of gestation and can involve various chromosomes and placental cell lineages. Confined placental mosaicism (CPM) is the result of postzygotic mitotic errors occurring in either diploid or trisomic zygotes. With trisomic zygote rescue, depending on the parental origin of the chromosome which is lost, uniparental disomy (UPD) or biparental disomy (BPD) may arise [Kalousek et al., Am J Hum Genet 52: 8-16, 1993]. In this paper, we present 14 pregnancies which were diagnosed by CVS as mosaic trisomy 7. All follow-up amniocenteses showed a normal diploid karyotype. Using both classical cytogenetics and interphase analysis, studies of term placentae showed variable levels of trisomy 7. DNA analysis was performed in nine cases to determine whether the diploid fetus had BPD 7 or UPD 7. Fetal UPD 7 was present only in one case; in eight other cases biparental inheritance was demonstrated. DNA analysis to establish the origin of trisomy 7 in the placenta was fully informative in six cases. One trisomy resulted from a meiotic error and was associated with fetal UPD 7, while the rest were somatic in origin. It is difficult to compare the effect of CPM for trisomy 7 to other trisomies confined to the placenta, as for most chromosomes there are few available cases. It appears that intrauterine fetal growth is not greatly affected by the presence of a trisomy 7 cell line in the placenta. This finding is in contrast to the serious effect of high levels of trisomy 16 within the placenta on fetal intrauterine growth in a series of well-documented cases of CPM 16 [Kalousek et al. 1993].

A fragile X mosaic male with a cryptic full mutation detected in epithelium but not in blood.

Individuals with developmental delay who are found to have only fragile X premutations present an interpretive dilemma. The presence of the premutation could be an unrelated coincidence, or it could be a sign of mosaicism involving a full mutation in other tissues. To investigate three cases of this type, buccal epithelium was collected on cytology brushes for Southern blot analysis. In one notable case, the blood specimen of a boy with developmental delay was found to have a premutation of 0.1 extra kb, which was shown by PCR to be an allele of 60 +/- 3 repeats. There was no trace of a full mutation. Mosaicism was investigated as an explanation for his developmental delay, although the condition was confounded by prematurity and other factors. The cheek epithelium DNA was found to contain the premutation, plus a methylated full mutation with expansions of 0.9 and 1.5 extra kb. The three populations were nearly equal in frequency but the 1.5 kb expansion was the most prominent. Regardless of whether this patient has clinical signs of fragile X syndrome, he illustrates that there can be gross tissue-specific differences in molecular sub-populations in mosaic individuals. Because brain and epithelium are more closely related embryonically than are brain and blood, cryptic full mutations in affected individuals may be evident in epithelial cells while being absent or difficult to detect in blood. This phenomenon may explain some atypical cases of the fragile X phenotype associated with premutations or near-normal DNA findings.

Longitudinal study of cognitive abilities and adaptive behavior levels in fragile X males: a prospective multicenter analysis.

Retrospective longitudinal studies have noted declines in IQ scores in many but not all fra(X) (fragile X) males and females. We report on a prospective investigation of longitudinal changes in cognitive ability (IQ) and adaptive behavior (DQ) in 24 fra(X) males from four test sites. Individuals who were tested ranged in age from 3-15 years. To determine cognitive ability, all males were administered the Stanford-Binet test (4th Edition). To assess adaptive behavior, all males were evaluated using the Vineland Adaptive Behavior Scales. Mean interest interval was 2.3 years. Using identical DNA protocols, all subjects were identified as bearing the fra(X) mutation. Results showed declines in IQ scores in 18/24 (75%) males. Four males showed no change in scores. Declines in DQ scores were noted in 22/24 (92%) of those tested. DQ scores were higher than IQ scores in 20/24 (83%) subjects. From a descriptive cohort analysis, decreases in IQ scores appear to follow a well-defined, negatively decelerating function. Declines in DQ were steeper and more nearly linear. Declining scores are not indicative of regression of intellectual and/or social skills, but of a relative inability to keep pace with their age-normed cohort. We conclude that the fra(X) mutation affects cognitive abilities in a uniform, nonlinear manner comparable to outcomes observed in earlier retrospective studies. Adaptive behavior also declines, but in a more linear fashion.

Lack of association between mutation size and cognitive/behavior deficits in fragile X males: a brief report.

Previously, researchers reported molecular-neurobehavioral or molecular-cognitive associations in individuals with fra(X) (fragile X) mutation. However, not all investigators have noted molecular-behavioral relationships. Consequently, we examined prospectively 30 fra(X) males age 3-15 years from four testing sites to determine whether there was a relationship between mutation size and degree of either cognitive or adaptive behavior deficit. To measure cognitive abilities, all individuals were administered the Stanford-Binet (4th edition) IQ test. To evaluate adaptive behavior (DQ) skills, all individuals were assessed using the Vineland Adaptive Behavior Scale. To determine fra(X) status, genomic DNA from all individuals was extracted and digested with EcoRI and EagI restriction enzymes. Southern blots were prepared and hybridized with the pE5.1 probe. The Pearson correlation coefficient between full mutation size and composite IQ score revealed a nonsignificant, near-zero association (r = 0.06; P > .76). The Pearson coefficient between mutation size and DQ also showed a nonsignificant, near-zero association (r = 0.06; P > .73). We conclude that while fra(X) mutation produces cognitive and behavior deficits in males who inherit the defective gene, there is no relationship between mutation size and degree of deficit.

Molecular fragile X screening in normal populations.

In December, 1993, we initiated a pilot project in which DNA fragile X (fraX) testing was offered during routine prenatal or genetic counseling to all pregnant women seen at the Genetics & IVF Institute, most of whom were referred for the indication of advanced maternal age. A brochure on fragile X syndrome was sent to each patient prior to her appointment and was reviewed by a counselor or physician during the counseling session. As of June 1995, 3,345 patients were offered testing; 474 women with no identified family history of mental retardation or learning disability and 214 women with a positive family history accepted the test on a self-pay basis. The second population screened was 271 potential donors in our anonymous egg donor program. DNA from blood was tested by Southern blot using EcoRI/EagI and StB12.3. If an expansion was detected, CGG repeat number was determined by PCR-based analysis. Among the 474 patients with unremarkable family histories, three fraX carriers were identified (repeat sizes = 60+), whereas none were found in the 214 patients with a positive family history. Among the potential egg donors, two high borderline patients were identified (repeat sizes = between 50 and 59). Our ongoing study indicates that screening of pregnant or preconceptual populations for fraX carrier status using DNA testing is accepted by many patients and is an important addition to current medical practice.

The fragile X premutation in carriers and its effect on mutation size in offspring.

The pattern of inheritance in the fragile X (fra(X)) mutation follows a multistage intergenerational process in which the premutation evolves into the full mutation and the characteristic phenotype of the fra(X) syndrome after passing through oogenesis or a postzygotic event. Findings from our multicenter study confirm a strong direct relationship between fra(X) premutation size in the mother and probability of a full mutation in offspring with the mutation. Remarkably, the best-fitting equations are nonlinear asymptotic functions. The close approximation to both the logistic model and Gompertz suggests a process of accumulation of errors in DNA synthesis, as has been proposed previously. We also note that a larger-than-expected number of daughters of transmitting males have premutations that are smaller than their fathers', and that proportion is significantly higher than the proportion of daughters whose premutations are smaller than their mothers'. Intergenerational decreases in premutation size have been reported in other trinucleotide-repeat disorders and also appear to be parent-of-origin specific. Thus, while intergenerational expansion to the full mutation in fra(X) may manifest a postzygotic event, decreases in mutation size may occur during or prior to meiosis.

Mental retardation and Ullrich-Turner syndrome in cases with 45,X/46X,+mar: additional support for the loss of the X-inactivation center hypothesis.

Four cases having mosaicism for a small marker or ring [45,X/46,X,+mar or 45,X/46,X,+r] chromosome were ascertained following cytogenetic studies requested because of minor anomalies (cases 1, 3, and 4) and/or short stature (cases 2 and 4). While all 4 cases had traits typical of Ullrich-Turner syndrome (UTS), cases 1, 3, and 4 had manifestations not usually present in UTS, including unusual facial appearance, mental retardation/developmental delay (MR/DD) (cases 3 and 4), and syndactylies (case 1). The facial appearances of cases 1 and 3 were similar yet distinct from that of case 4. Using fluorescence in situ hybridization (FISH), each of the markers in these 4 cases was identified as having been derived from an X chromosome. The level of mosaicism for the mar/r(X) cell line in these cases varied from 70% (case 1) to 16% (case 4) but was not apparently correlated with the presence of MR/DD. Replication studies demonstrated a probable early replication pattern for the mar/r(X) in cases 1, 3, and 4, while the marker in case 2 was apparently late replicating. To date, 41 individuals having mosaicism for a small mar/r(X) chromosome have been described. Interestingly, most of the 14 individuals having a presumedly active mar/r(X) demonstrated clinical findings atypical of UTS, including abnormal facial changes (11) and MR/DD (13). MR was noted most frequently in those cases having at least 50% mosaicism for the marker or ring. In contrast, atypical UTS facial appearance or MR/DD was not noted in 14 of the 16 cases with UTS who carried a probable late replicating marker or ring. In conclusion, although the phenotype of 45,X/46,X,mar/r(X) individuals appears to be influenced by the genetic content and degree of mosaicism for the mar/r(X), the most significant factor associated with MR/DD appears to be the activity status of the mar/r(X) chromosome. Thus, our 4 cases provide further support for the hypothesis that a lack of inactivation of a small mar/r(X) chromosome may be a factor leading to the MR and other phenotypic abnormalities seen in this subset of individuals having atypical UTS.