Structural organization and DNA methylation patterning within the mouse L1 family.

We have studied stable differences in patterns of DNA methylation seen in the repeated sequences of mouse cells. A cloned 1330-base pair fragment of mouse repetitive DNA (pFS-13) was used as a probe in Southern blotting experiments. Mouse spleen and L1210 lymphoma DNA appeared to be normally methylated at HpaII sites probed by this sequence. Friend erythroleukemia cell, and Sp2 cell DNA both showed an abnormal banding pattern in HpaII digests. Hybridization in situ to metaphase chromosomes showed that probed sequences were broadly interspersed along the arms of each mouse chromosome. The DNA sequence of the 1330-base pair insert in the clone was determined; a copy of the R sequence of L1 was found at its 5' end. Walking experiments using M13 subclones from pFS-13 permitted the construction of a map for d(pCCGG) sites at the 3' end of the mouse L1 family. The unmethylated d(pCCGG) sites in Sp2 and Friend cells could then be assigned to polymorphic-repeated sequence groups within L1, homologous to the region spanned by BAM5 and R. Since there are several thousand copies of each of the fragments seen in autoradiographs, these sequences must possess a common methylation state at many genomic locations. Concerted (nonrandom) hypomethylation of certain subfamilies of L1 appears to be a stable characteristic of several cell lineages. These findings suggest that certain L1 families possess commonalities that permit and perhaps require differential DNA methylation in established cell lineages.

Primate evolution of a dispersed human repetitive DNA sequence.

A dispersed middle repetitive DNA sequence isolated originally from human chromosome 12 did not show homology with rodent DNA under standard conditions of Southern DNA blot analysis. The evolutionary relationship of this human repetitive DNA to that of other primates was investigated using three hybridization methods: DNA dot blot, Southern DNA blot analysis, and chromosome in situ hybridization. Homology with the human repetitive DNA was found throughout the suborder Anthropoidea, in fourteen ape and New and Old World monkey species. In addition, the human pattern of hybridization to noncentromeric regions of all chromosomes was seen. No hybridization by any of the three techniques was found in five species of the suborder Prosimii. The phenomenon of marked differences in sequence homology and copy number of dispersed repetitive DNA from closely related species has been observed in protozoans (Plasmodia), Drosophila, sea urchins, mice and the great apes (Hominoidea). We report here a similar phenomenon that may have occurred at an early stage in primate evolution.

Chromosome deletion mapping of interspersed low-copy repetitive DNA.

A cloned 2.2 Eco RI segment of interspersed repetitive DNA was hybridized to genomic DNA from a mentally retarded patient with an interstitial deletion in the long arm of one chromosome 12 (12q-). Under hybridization conditions of high stringency, one prominent 2.2-kilobase (kb) Eco RI fragment demonstrated reduced autoradiographic intensity in the 12q- sample compared with several normal controls. These findings indicate that the genomic location for one of the highly or perfectly homologous 2.2-kb Eco RI fragments is in chromosome region 12q21q22, and suggest that a low-copy repetitive DNA probe as used here may have practical utility, as in detecting small deletions or other chromosome alterations.

Y chromosome length related to fetal loss.

The Y/20 ratio (length of Y chromosome/length of chromosome 20) was examined among 216 males, 108 of whose wives had a history of repeated abortions (study group), and 108 who were mentally retarded (controls). There was no significant difference in frequency of long Y (Y/20 equal to or greater than 1) between the study group and controls. Also, there was the expected male: female ratio among normal living children of couples in the study group, and the Y/20 ratio was not significantly increased among fathers with abnormal male offspring. However, wives of long Y males were more likely to have at least one abnormal male birth, compared with other wives (this approached statistical significance, p less than 0.08). In addition, a significantly higher frequency of long Y was found in a subset of affected males whose wives had 2 or more spontaneous abortions plus some other abnormal pregnancy outcome. Although the findings reported here do not strongly support a causal relationship, they at least suggest an association between long Y chromosome and abnormal fetal development.

Linkage analysis of neurofibromatosis (von Recklinghausen disease).

Linkage analysis of 28 genetic markers was undertaken in 108 subjects from 11 families with well-documented, classic, peripheral neurofibromatosis. Fifty-four persons were affected in one four-generation family, seven three-generation families, and three two-generation families. Lod scores were calculated using the standard LIPED programme for 49 combinations of theta male and theta female from 0.01 to 0.50. Lod scores excluded close linkage with 16 markers, including most tested on chromosome 1 and HLA on chromosome 6, and were inconclusive for 12 markers, including the secretor locus, closely linked to myotonic dystrophy. Analysis of five informative families resulted in a lod score of +2.2 for close linkage with GC on chromosome 4. However, the lod score for GC in the one additional informative family was negative, so that the final interpolated maximum was Z = 0.89 for theta male = 0.03, theta female = 0.28. Further studies are needed to evaluate this suggestion of linkage and possible genetic heterogeneity.

Parental reproductive problems and gestational hormonal exposure in autistic and schizophrenic children.

The incidence of infertility and two or more spontaneous abortions was significantly increased in the parents, compared to that reported for the general population, in this pilot survey of 61 patients evaluated for major childhood psychoses. In addition, 18% of our patients had a history of early gestational exposure to progesterone/estrogen compounds (9 patients) and to cortisone (2 patients). This frequency of gestational hormoné exposure was significantly increased over that in normal infants from three published surveys. However, in 5 of the 11 patients with gestational hormonal exposure, the medication was prescribed because of prior parental reproductive problems or bleeding during the current pregnancy. Therefore, it cannot be concluded that the gestational hormonal exposure was causally related to the psychoses present in these patients. In order to obtain more conclusive data, there will need to be continued monitoring of parental reproductive histories and gestational environmental exposures in autistic and schizophrenic children.

Gene for hereditary retinoblastoma assigned to human chromosome 13 by linkage to esterase D.

Evaluation of three families with hereditary retinoblastoma demonstrates close linkage of the gene for this tumor with the genetic locus for esterase D. These results assign the gene for the hereditary form of retinoblastoma to band q14 on chromosome 13, the same region which is affected in the chromosome deletion form of this eye tumor, and therefore suggest a common underlying mechanism in the pathogenesis of these two forms of retinoblastoma.

Trisomy 20p due to a paternal reciprocal translocation.

A mentally retarded boy with multiple malformations was found to have trisomy for the distal two-thirds of the short arm of chromosome 20 (trisomy 20p), resulting from a paternal translocation (5;20)(p15;p11). The patient had a cleft palate, a feature not present in other trisomy 20p patients. A review of the reported trisomy 20p patients indicates that their varied features do no constitute a readily recognizable clinical syndrome.

Familial Y-autosome translocation in two unrelated girls.

Two unrelated girls presenting with developmental delay were found to have familial Y-autosome translocations. The first had a Y;15 and the second a Y;22 translocation, involving only the Y heterochromatin on the basis of Q, C, SS, distamycin A and DAPI techniques. The first patient died of a medulloblastoma and at autopsy was found to have an adrenal neuroganglioma. The Y-autosome translocations in the affected patients were identical to those in their respective normal fathers (who had normal Y chromosomes as well). The absence of detectable translocated euchromatin from the subcentromeric region of the Y chromosome is consistent with normal female external genitalia and the absence of germ cell tumors in both patients. Whether the nongonadal neoplasias and hypoplastic uterus and ovaries in the first patient were related to the Y;15 translocation remains uncertain.

9p duplication confirmed by gene dosage effect: report of two patients.

We report two cases duplication of 9p. This investigation was prompted by the identification of two patients with minor congenital anomalies and mental retardation. Chromosomal karyotype in both patients revealed 9p duplication, one as a result of tandem duplication of 9p at band p13 leads to p24 and the other due to an extra and deleted chromosome number 9 (pter leads to cent leads to q13). Both patients has elevated galactose-1-phosphate-uridyl-transferase level demonstrating additional evidence for mapping GALT on the short arm of chromosome 9.

Pentasomy X: report of patient and studies of X-inactivation.

A five-year-old girl presented with mental retardation (MR), microcephaly, short stature, ptosis, malocclusion, abnormal elbows, fifth finger clinodactyly, joint hyperextensibility in hands and feet, renal hypoplasia, nonobstructive ureteral stasis, pyelonephritis, and renal failure. Five X chromosomes (49,XXXXX) were found in all peripheral blood lymphocytes and skin fibroblasts examined. Xa RBC typing, utilizing serial dilutions of antiserum, gave agglutination at a higher titer than in either Xg(a+) positive parent; the patient's serum IgM was also elevated. These immunological findings imply a lack of dosage compensation and incomplete inactivation of some X-linked loci.

Expression of GALT in 9p chromosome alterations: assignment of GALT locus to 9cen leads to 9p22.

Determination of activity and electrophoretic mobility of GALT in patients with various chromosome 9 deletions and duplications confirms the assignment of its locus to 9p and suggests its locus is in the segment 9cen leads to p22. Two inversions of 9qh (inv(9)(p11q12)) did not alter GALT expression.

Outcome of pregnancies complicated by early vaginal bleeding.

Obstetrical and neonatal data were analysed for pregnancy outcome in 259 deliveries complicated by first or second trimester vaginal bleeding. There was a high incidence of low birth weight, low gestational age, perinatal death, asphyxia, breech delivery, placental infarcts and small-for-dates term infants. Fetal anomalies were slightly though not significantly increased. Combined suboptimal pregnancy outcome occurred in 29.7 per cent of these deliveries compared to 15.2 per cent of 25 118 concurrent deliveries without reported early pregnancy bleeding (p less than 0.0001). The combined risk remained approximately doubled even for primigravidae and for women without prior illness or pregnancy complications. The highest combined risk, 61.5 per cent, was for women with at least two prior abortions, premature births or perinatal deaths and no prior term births. These findings suggest that early gestational vaginal bleeding is one predictor of suboptimal pregnancy outcome.

C-band polymorphism: comparison between trisomy 21 cases and mentally retarded controls.

C-banding was done prospectively on 50 Down syndrome (trisomy 21) cases and 50 mentally retarded controls. Heterochromatin was quantitated by measuring the lengths of heterochromatin blocks and comparing these segments to the length of the short arm of chromosome 16 for 1, 9 and 16 heterochromatin, and to the total length of the Y chromosome for the Y heterochromatin in the distal long arm. For the first 30 individuals in each group, there was no difference in the mean lengths of C-band blocks of the 1, 9, 16 and Y chromosomes. For the total sample, there also was no difference between the trisomy 21 cases and controls in the number or size of pericentric inversions involving the heterochromatin blocks of chromosomes 1 and 9. Assuming random segregation of the parental C-band polymorphisms, this study gives no evidence for an association between such polymorphisms of the 1, 9, 16 and Y chromosomes and nondisjunction of chromosome 21.

Phenotypic variation in two patients with a ring chromosome 22.

Two severely mentally retarded patients with a ring chromosome 22 presented with disparate phenotypes: one patient manifested only minimal dysmorphic features, whereas the other had a distinctive pattern of anomalies consisting of an abnormal skull configuration with mild maxillary hypoplasia, a large nose, thick full lips, a protruding tongue, lymphedema, hypotonia and an unsteady gait. The findings in these and previously reported patients indicate that a ring chromosome 22 is usually associated with moderate to severe mental retardation, with a range of dysplastic features from mild and nonspecific to more marked and distinctive.