Maternal serum alpha-fetoprotein screening and fetal chromosome anomalies: is lowering maternal age for amniocentesis preferable?

We have compared the cytogenetic abnormalities diagnosed prenatally in 1,098 patients referred for amniocentesis because of low maternal serum alpha-fetoprotein (MSAFP) to those of 445 patients whose indication was elevated MSAFP and those of 361 patients who had amniocentesis for "maternal anxiety." Autosomal trisomies, sex chromosome aberrations, and various structural rearrangements were detected in all 3 groups and actually exceeded the age-related incidence estimates. The frequency of chromosome anomalies in cases studied because of "maternal anxiety" with no prior screening was similar to that in the group referred for low MSAFP (1.38 and 1.27%, respectively). A relatively higher frequency (2.02%) was detected in the group whose indication was elevated MSAFP. Maternal serum screening is designed primarily to recalculate risk figures for Down syndrome, but not for other major chromosome abnormalities. The concept of prenatal screening for chromosome aberrations must therefore be reevaluated. We think that efforts should be directed at making amniocenteses more accessible to patients who request it. "Lowering" maternal age limits to 30 would encompass a greater proportion of pregnancies at risk and would be a step toward more effective prenatal diagnosis for chromosome abnormalities.

Loss of subtelomeric sequence associated with a terminal inversion duplication of the short arm of chromosome 4.

We report on a 4(1/2)-year-old girl, who presented with multiple minor anomalies consistent with trisomy for 4p. GTG-banding identified a de novo terminal inversion duplication of distal 4p, dup(4)(p16.3p15.3). Fluorescence in situ hybridization (FISH) with a wcp4 probe confirmed the chromosome 4 origin of the additional material. FISH with a 4p subtelomere probe, D4F26, showed no signal on the dup(4) chromosome identifying a deletion of this region. Molecular analysis of 4p STS loci confirmed the subtelomeric deletion and showed loss of the paternal allele in this region. The paternal origin of the deleted region and homozygosity for one of the two paternal alleles within the region of the duplication suggests that a sister chromatid rearrangement on the paternal chromosome 4 was involved in the formation of the dup(4) chromosome. To date, the best characterized mechanisms of formation of chromosome duplications are terminal inversion duplications of 8p, which were shown to be derived from rearrangements at maternal meiosis-I. Our data show that mechanisms other than a maternal meiosis-I rearrangement can lead to the formation of terminal inversion duplications. FISH analysis with the appropriate subtelomeric probes is warranted in terminal inversion duplications to check for associated deletions.

Paternal uniparental disomy for chromosome 14: a case report and review.

Uniparental disomy (UPD) for several chromosomes has been associated with disease phenotypes. Maternal UPD for chromosome 14 has been described and has a characteristic abnormal phenotype. Paternal UPD14 is rare and only three previous cases have been reported. We describe a new case of paternal UPD for chromosome 14 in an infant with a 45,XX,der(13q;14q) karyotype, which was confirmed by molecular analysis. The proposita had findings similar to those of the previous cases of patUPD14 and we conclude that there is a characteristic patUPD14 syndrome most likely due to imprinting effects. Couples with Robertsonian translocations involving chromosome 14 should be counseled as to the possibility of UPD14 and the option of prenatal diagnosis when indicated.

Prenatal cytogenetic diagnosis: first 1,000 successful cases.

From February 1969 to August 1976, we studied 1,048 amniotic fluids. Of these, 958 (91.4%) were primarily for prenatal cytogenetic diagnosis. Cytogenetic studies were attempted in 1,021 cases; the diagnosis was successful in 1,000 of these. The failure rate of obtaining a diagnosis from the amniotic fluid cell culture of the first amniocentesis was 5% (50 cases); 29 cases had a repeat tap and successful diagnosis was achieved in all. In 21 cases, a repeat tap was refused. Thus, the overall failure rate of obtaining a final cytogenetic diagnosis was 2.06% (21/1,021). There were 32 fetal losses after amniocentesis including 16 spontaneous second trimester abortions, 7 fetal deaths in utero and 9 stillbirths. In two additional cases, fetal death had occurred before amniocentesis. This number of fetal losses does not exceed the number that would be expected in the same maternal age group without amniocentesis. In our series, the frequencies of trisomy in maternal age groups 40 years and over, 37-39 years, 35-36 years, and under 35 years were 4.5, 3.14, 0 and 0% respectively. These frequencies are comparable to those reported from other prospective prenatal studies and higher than those of retrospective live born studies. Various problems and pitfalls in prenatal cytogenetic diagnosis are discussed.

Prenatal diagnosis of renal anomalies.

Within the past 24 months, we have performed prenatal diagnostic studies in 4 pregnancies known to be at risk for well-described genetic syndrome involving renal abnormalities, ie, Meckel syndrome, Roberts syndrome, and bilateral renal agenesis. The diagnostic techniques utilized were ultrasonographic scanning (B-mode and grey scale), biochemical assays, and radiographic evaluation. The ultrasound finding common to the 3 affected cases was extreme oligohydramnios, which we considered indirect evidence that renal anomalies were present. The ultrasound scans of the fetuses affected with Meckel and Roberts syndrome demonstrated anechoic cystic spaces in the abdomen, representing the enlarged dysplastic cystic kidneys. An encephalocele was well demonstrated by B-mode scan in the fetus with Meckel syndrome. The absence of normal limbs in the Roberts syndrome was evident on serial grey scale scans of the fetus. Biochemical and radiographic studies provided results consistent with the suspected diagnoses. The importance of providing genetic counseling and prenatal diagnosis to families at risk is emphasized.

Unilateral microscopic gonadoblastoma in a prepubertal Turner mosaic with Y chromosome material identified by restriction fragment analysis.

A high incidence of gonadal tumors has been demonstrated in patients with gonadal dysgenesis in the presence of Y chromosome material. A unilateral, microscopic gonadoblastoma was found in the dysgenetic gonad of a ten-year-old, phenotypic female, with Turner stigmata and chromosome mosaicisms of three cell populations 45,X/46,X,+mar,/47,X,+mar,+mar. It is often impossible to determine by cytogenetic analysis if the marker chromosome has derived from the X or Y chromosome. The origin of these marker chromosomes was elucidated by the use of DNA probe (pDP34) for male-specific sequences of the Y chromosome. The presence of Y-specific fragments in the patient's DNA led to surgical exploration and the detection of a gonadoblastoma.

Prenatal diagnosis of bilateral renal agenesis.

Bilateral renal agenesis (BRA), or Potter's syndrome, is a rare genetic disorder in which agenesis of the kidneys is associated with pulmonary hypoplasia and characteristic facial features. Oligohydramnios or virtual absence of amniotic fluid is found in most pregnancies with BRA. Clinical observation and serial ultrasonography scans made it possible to diagnose BRA prenatally in a fetus at risk. Postmortem examination confirmed the diagnosis.

Autosomal dominant inheritance of retinoschisis.

Hereditary retinoschisis affected eight members of three generations of a family. The mode of transmission and the clinical features were not compatible with findings noted in either X-chromosome-linked or autosomal recessive forms of retinoschisis. The genetic and clinical features in this family strongly supported autosomal dominant inheritance, adding to the known genetic heterogeneity for the hereditary forms of retinoschisis. The expression of the condition varied in severity, but all affected members of the family had peripheral retinoschisis and peripheral retinal degeneration. Three had maculoschisis and five had macular pigmentary changes. Electroretinographic findings were normal in six of the eight.

A revisit of trisomy 20 mosaicism in prenatal diagnosis--an overview of 103 cases.

One hundred and three cases with prenatal diagnosis of trisomy 20 mosaicism through amniocentesis were reviewed. Approximately 90 per cent (90/101) of the cases were associated with grossly normal phenotype. It is likely that, in the majority of cases, cells with trisomy 20 were extraembryonic in origin or largely confined to the placenta. However, in some cases, the cells with trisomy 20 were confined to certain specific fetal organs or tissues such as kidney, skin, etc. Cytogenetic follow-up studies in liveborns should include a culture from urine sediment.

Trisomy 20 mosaicism in prenatal diagnosis--a review and update.

A total of 66 cases with prenatal diagnosis of trisomy 20 mosaicism was reviewed. Since the majority of cases (85 per cent) was associated with grossly normal phenotype and the abnormalities noted in 15 per cent of cases were inconsistent and rather non-specific, no casual relationship between trisomy 20 mosaicism and a specific malformation syndrome can be established. The possibility of an association between an abnormal phenotype and a high percentage of trisomy 20 cells (greater than 60 per cent) must be considered preliminary and be viewed with caution. The fact that cells with trisomy 20 have not been recovered from blood cultures and were detected more frequently from specific fetal tissues, (such as kidney, rectum, oesophagus), and from placental tissues, suggests that trisomy 20 is more likely to be confined to certain fetal organs and to extra-embryonic tissues. This review calls for the collection of more data on all cases of trisomy 20 mosaicism diagnosed prenatally, in order to provide more accurate information to the prospective parents.

Amniotic fluid alpha-fetoprotein levels and prenatal diagnosis of autosomal trisomies.

Pregnancies with fetal trisomy 21 have been associated with low amniotic fluid alpha-fetoprotein levels (AFAFP). This observation led to the suggestion that low AFAFP levels be used as a criterion for completion of a chromosomal analysis in patients who are not otherwise at increased risk for a fetal chromosome abnormality and in whom karyotyping might not have been completed for economic reasons. In order to assess the usefulness of such criteria, we reviewed the AFAFP levels of 90 cases of fetal trisomy 21, 23 cases of trisomy 18, and 10 cases of trisomy 13. These were compared with 2400 control samples with normal chromosome constitution. AFAFP levels were generally lower in pregnancies with trisomy 21, showing a median value of 0.72 MoM. However, 40 per cent of the trisomy 21 samples had AFAFP values greater than 0.8 MoM and 20 per cent were over 1.0 MoM. These data imply that over 50 per cent of Down syndrome cases might have been missed using a cut-off level of 0.70 MoM for completion of chromosome analysis. Using a higher cut-off level will leave only a small percentage of samples unkaryotyped. The distribution of AFP levels in trisomy 13 and 18 is no different from controls; we therefore believe that fetal karyotyping should be completed in every amniotic fluid sample obtained.

Association of 5q- and refractory anemia.

The association of refractory anemia with partial deletion of the long arm of one No. 5 chromosome (5q-) has been reported in six patients within the last two years. We wish to report an additional patient with refractory anemia and an acquired chromosomal deletion, del(5)(q15), in a direct bone-moarrow preparation. The specificity of this deletion for refractory anemia is discussed. It remains to be seen whether patients with refractory anemia and 5q- tend to develop acute leukemia, as has been recently suggested.

A heterozygous defect for structurally altered pro-alpha 2 chain of type I procollagen in a mild variant of osteogenesis imperfecta. The altered structure decreases the thermal stability of procollagen and makes it resistant to procollagen N-proteinase.

Cultured skin fibroblasts from a proband with an autosomal dominant variant of osteogenesis inperfecta were found to synthesize approximately equal amounts of normal pro-alpha 2(I) chains of type I procollagen and pro-alpha 2(I) chains which migrated more rapidly when examined by polyacrylamide gel electrophoresis in sodium dodecyl sulfate. The structural alteration was present in alpha 2(I)-CB4, a cyanogen bromide fragment containing amino acid residues 7-327 of the alpha 2 chain, and it appeared to be a deletion of about 30 amino acids. The pro-alpha 2(I) chains with the apparent deletion associated with normal pro-alpha 1(I) chains synthesized by the same fibroblasts and formed triple-helical type I procollagen. The presence of the altered pro-alpha 2 chains in trimers of procollagen had two consequences in terms of the physical properties of the molecule. One was to decrease the thermal stability of the protein as judged by resistance to proteolysis at 37 degrees C and by the helix to coil transition as assayed by circular dichroism. The second consequence was to make type I procollagen containing the shortened pro-alpha 2(I) chains resistant to digestion by procollagen N-proteinase. The simplest explanation for the data is that the apparent deletion in half the pro-alpha 2(I) chains produced a partial unfolding of the N-terminal region of type I procollagen which prevented processing of the protein by procollagen N-proteinase.

Prenatal diagnosis of 5p-.

With the combination of the various banding techniques (G,Q, and R), a small deletion of the short arm of a No.5 chromosome was detected prenatally in the pregnancy of a 39-year-old woman. The deletion appeared to be either intersitial in nature, involving part of p13 and p14, or the result of a translocation with deletion of p13 leads to pter. Both parents were found to have a normal chromosome constitution with normal banding patterns. Thus, this deletion was a de novo event. Repeat amniotic fluid cell chromosome analysis at the time of elective abortion, and postmortem examination of the fetus confirmed the prenatal cytogenetic diagnosis. We wish to emphasize that precise identification of a small deletion, as in this case, requires a combination of the various banding techniques.

Microcephaly and congenital nephrotic syndrome owing to diffuse mesangial sclerosis: an autosomal recessive syndrome.

Three sibs born to consanguineous parents had congenital nephrotic syndrome, microcephaly, and psychomotor retardation. Pathology of the kidneys showed diffuse mesangial sclerosis with deposits of IgG and C3 in the mesangium and glomerular basement membranes. All three children died before the age of 3 years. Of 19 published cases of children with the association of congenital nephrotic syndrome and microcephaly, only four had histological evidence of diffuse mesangial sclerosis, and two of their sibs probably had the same disease. The association of nephrotic syndrome owing to congenital diffuse mesangial sclerosis, microcephaly, and mental retardation appears to be a distinct syndrome with an autosomal recessive mode of inheritance.

Interstitial deletion of the long arm of chromosome 6 [del(6) (q16q22)]: case report and review of the literature.

Partial monosomy of 6q resulting from an interstitial deletion of bands q16----q22 was found in a 12-year-old boy manifesting mental retardation, seizure disorder, and dysmorphic features. The correlation of phenotypic expression and specific long arm deletions of chromosome No. 6 is discussed.

Clinical applications of comparative genomic hybridization.

PURPOSE: Comparative genomic hybridization (CGH) is a powerful DNA-based cytogenetic technique that allows the entire genome to be scanned for chromosomal imbalances without requiring the sample material to be mitotically active. During the past 2 years we received many requests from various medical centers around the country to use CGH to resolve the identity of aberrant chromosomal material. METHODS: We report the use of CGH for the evaluation of 12 clinical postnatal cases in which traditional cytogenetic analysis yielded ambiguous results. This series consisted of five marker chromosomes, five unbalanced translocations, and two intrachromosomal duplications. RESULTS: Identification and characterization of the additional unknown chromosomal material was achieved with use of CGH. All CGH findings were validated by traditional fluorescence in situ hybridization and other specialized staining techniques. CONCLUSLONS: These results demonstrate the effective use of CGH as a focused, single-step method for the identification of chromosomal material of unknown origin.

Partial deletion of long arm of chromosome 11: del (11) (q23).

The cytogenetic analysis of an infant with multiple congenital anomalies revealed a small deletion of the long arm of one No. 11 chromosome: 46,XX,del(11)(q23). The main clinical manifestations included: ocular colobomata, absent philtrum, severe congenital heart disease, contractures of the large joints and skin pigmentation. Both parents showed a normal chromosome constitution. In comparison to the previously reported cases of 11q-, the patient presented here had more severe congenital anomalies. The correlation of the size of the deletion, and the location of the break, with the physical findings is discussed.

Supernumerary small ring chromosome.

A supernumerary small ring chromosome was found in 30% of cultured peripheral leucocytes and 50% of skin fibroblasts in a 6-year-old boy with mild mental retardation and midline cleft palate. The extra chromosome appeared to carry a densely staining region on Giemsa banding. The banding patterns of the remaining 46 chromosomes were normal. C banding indicated that the ring chromosome contained mainly centromeric constitutive heterochromatin. Chromosome analysis of both parents showed normal karyotypes by both conventional and banding techniques; thus the origin of the ring chromosome could not be determined.