The carrier frequency of the BRCA1 185delAG mutation is approximately 1 percent in Ashkenazi Jewish individuals.

Since BRCA1, the first major gene responsible for inherited breast cancer, was cloned, more than 50 unique mutations have been detected in the germline of individuals with breast and ovarian cancer. In high-risk pedigrees, female carriers of BRCA1 mutations have an 80-90% lifetime risk of breast cancer, and a 40-50% risk of ovarian cancer. However, the mutation stats of individuals unselected for breast or ovarian cancer has not been determined, and it is not known whether mutations in such individuals confer the same risk of cancer as in individuals from the high-risk families studied so far. Following the finding of a 185delAG frameshift mutation in several Ashkenazi Jewish breast/ovarian families, we have determined the frequency of this mutation in 858 Ashkenazim seeking genetic testing for conditions unrelated to cancer, and in 815 reference individuals not selected for ethnic origin. We observed the 185delAG mutation in 0.9% of Ashkenazim (95% confidence limit, 0.4-1.8%) and in none of the reference samples. Our results suggest that one in a hundred women of Ashkenazi descent may be at especially high risk of developing breast and/or ovarian cancer.

Adult hemoglobin synthesis by reticulocytes from the human fetus at midtrimester.

The synthesis of adult-type hemoglobin was measured in small samples of peripheral blood cells from 9- to 18-week human fetuses. Hemoglobin indistinguishable from hemoglobin A was identified by ion-exchange chromatography, electrophoresis at pH 8.6, tryptic peptide analysis, and the insensitivity of its synthesis to the action of O-methylthreonine. Synthesis of hemoglobin A accounted for 8 to 14 percent of total hemoglobin synthesis and was demonstrated in as little as 10 microliters of fetal blood. These studies provide sensitive methods for the detection of beta chain types in hemoglobin synthesized by the human fetus at midtrimester. If methods to obtain small quantities of fetal blood at midtrimester become available, these techniques should be applicable to the antenatal detection of sickle cell anemia and related hemoglobinopathies.

Xeroderma pigmentosum: a rapid sensitive method for prenatal diagnosis.

When normal human cells, capable of repairing ultraviolet-induced lesions in their DNA, are incubated in the thymidine analog 5-bromodeoxyuridine after ultraviolet irradiation, the analog is incorporated into the repaired regions. When such repaired cells are subsequently irradiated with 313-nanometer radiation and placed in alkali, breaks appear in the DNA at sites of incorporation of 5bromodeoxyuridine, inducing a dramatic downward shift in the sedimentation constant of the DNA. Cells from patients with the disease xeroderma pigmentosum, which causes sensitivity to ultraviolet, are incapable or only minimally capable of repair; such cells incorporate little 5-bromodeoxyuridine into their DNA under these conditions and, upon 313-nanometer irradiation and sedimentation in alkali, exhibit only minor shifts in DNA sedimentation constants. When fibroblasts developed from biopsies of normal skin and of skin from patients with xeroderma pigmentosum, as well as cells cultured from midtrimester amniotic fluid, were assayed in this fashion unequivocal differences between normal and xeroderma pigmentosum cells were shown. Xeroderma pigmentosum heterozygotes are clearly distinguishable from homozygous mutants, and results are available 12 hours after irradiation.

Metachromatic leukodystrophy: comparison of early-and late-onset forms.

Comparative study of peripheral nerve biopsies and cultured skin fibroblasts from patients with late infantile and early adult-onset forms of metachromatic leukodystrophy revealed similar pathologic changes in the early stages of nerve degeneration. However, the peripheral nerves in the adult-onset cases eventually reached a more chronically demyelinated fibrotic state than did nerves in the infantile cases. Cultured skin fibroblasts from the adult-onset patients, although clearly abnormal, were able to catabolize sulfatide significantly more effectively than the cultured skin fibroblasts from late infantile patients.

Chromosome Abnormalities in infants with prune belly anomaly: association with trisomy 18.

Two infants are described with "prune belly anomaly" (PBA) and concomitant trisomy 18. Severe abdominal distention was detected prenatally in one by ultrasonographic study, and in the second child at birth. Other chromosome abnormalities previously associated with PBA also are reviewed. The prune belly anomaly constitutes a malformation sequence that is causally nonspecific and which may occur in diverse aneuploidy syndromes. Aneuploidy is important to detect in prenatally diagnosed cases in which intrauterine fetal treatment is being considered.

Stimulation of amniotic fluid cell growth by cartilage growth factor.

Cartilage growth factor (CGF) stimulates the growth of primary and secondary cultures of human amniotic fluid cells. Over a 14--16-day period there is an approximately 70% enhancement in the number of cells in primary cultures and a 170% increase in secondary cultures. Neither the karyotype or the specific activities of lysosomal enzymes are altered by the presence of CGF in the medium.

Marker chromosomes: cytogenetic characterization and implications for prenatal diagnosis.

Satellited marker chromosomes were identified in four individuals from unrelated families; one was first encountered in cultured amniotic fluid cells obtained for prenatal diagnostic studies. We present cytogenetic characterization of these marker chromosomes and clinical findings in the individuals carrying them. Identification of a marker chromosome in amniotic fluid cell cultures presents problems in genetic counseling, as it is often difficult to determine the clinical significance of such a finding. Chromosome-banding techniques now allow the precise identification of satellited marker chromosomes originating from chromosome 15. Presence of a supernumerary bisatellited der(15) marker chromosome containing the proximal long arm of 15 has been associated with mental and developmental retardation. Application of chromosome-banding techniques was useful in characterization of the marker chromosomes and providing prenatal genetic counseling.

Maternal serum hexosaminidase A in pregnancy: effects of gestational age and fetal genotype.

The diagnostic usefulness of sulfated fluorogenic substrates in carrier detection of Tay-Sachs disease in serum during pregnancy was assessed by testing coded samples. Gradual increase in serum hexosaminidase activities toward these substrates was observed throughout pregnancy in both carrier and non-carriers of the Tay-Sachs gene, but absolute discrimination between the 2 genotypes could not be achieved even when values were compared within the same gestational age. Examination of isolated isozyme fractions with the sulfated substrates showed that the increased activities during pregnancy were due to a genuine increase in hexosaminidase A and not associated with the elevation of hexosaminidase I (or P), which was evident only with unsulfated substrates. The extent of the increase was influenced by the genotype of the fetus as indicated by higher values in pregnant carriers who carried non-carrier fetuses. We conclude that determination of serum hexosaminidase A during pregnancy by sulfated fluorogenic substrates may have a prenatal diagnostic value when used in obligate heterozygotes for Tay-Sachs disease, but is unreliable for screening purposes.

Evaluation of mental retardation: recommendations of a Consensus Conference: American College of Medical Genetics.

A Consensus Conference utilizing available literature and expert opinion sponsored by the American College of Medical Genetics in October 1995 evaluated the rational approach to the individual with mental retardation. Although no uniform protocol replaces individual clinician judgement, the consensus recommendations were as follows: 1. The individual with mental retardation, the family, and medical care providers benefit from a focused clinical and laboratory evaluation aimed at establishing causation and in providing counseling, prognosis, recurrence risks, and guidelines for management. 2. Essential elements of the evaluation include a three-generation pedigree: pre-, peri-, and post-natal history, complete physical examination focused on the presence of minor anomalies, neurologic examination, and assessment of the behavioral phenotype. 3. Selective laboratory testing should, in most patients, include a banded karyotype. Fragile X testing should be strongly considered in both males and females with unexplained mental retardation, especially in the presence of a positive family history, a consistent physical and behavioral phenotype and absence of major structural abnormalities. Metabolic testing should be initialed in the presence of suggestive clinical and physical findings. Neuroimaging should be considered in patients without a known diagnosis especially in the presence of neurologic symptoms, cranial contour abnormalities, microcephaly, or macrocephaly. In most situations MRI is the testing modality of choice. 4. Sequential evaluation of the patient, occasionally over several years, is often necessary for diagnosis, allowing for delineation of the physical and behavioral phenotype, a logical approach to ancillary testing and appropriate prognostic and reproductive counseling.

Serum pyruvate-kinase (PK) and creatine-phosphokinase (CPK) in progressive muscular dystrophies.

PK and CPK have been determined in the serum from 208 individuals including 70 normal controls (61 adults and 9 children) and 138 patients with a variety of neuromuscular disorders. In adult controls the mean activity (+/- SE) for PK is 1.2 +/- 0.05 mumol/ml/h. In normal children PK activity was about twice as high as in normal adults and decreases with increasing age. In 26 patients with Duchenne dystrophy the range of serum PK was 4.0-150.4 and in 17 individuals with the Becker type, 3.0 to 148.7. All had elevated PK and CPK levels. Eighteen of 20 patients with the facio-scapulo-humeral (FSH) from of muscular dystrophy had increased PK while only 9 had elevated CPK. Regression analyses have shown an inverse correlation between PK levels and age (or degree of disability in DMD). Kinetic and electrophoretic studies indicate that the PK isozyme found in the serum from affected patients and from heterozygotes for the DMD gene is mainly the M1 type PK, which is the only PK isozyme found in skeletal muscle and brain and the major component from myocardium.

Serum pyruvate-kinase (PK) and creatine-phosphokinase (CPK) in female relatives and patients with X-linked muscular dystrophies (Duchenne and Becker).

Determination of serum creatine phosphokinase (CPK) activity is often used in efforts to detect carriers of X-linked muscular dystrophies. We have recently demonstrated that another serum enzyme, pyruvate-kinase (PK) may also be of use in the diagnosis of patients affected with a variety of neuromuscular disorders. To evaluate the usefulness of this assay for carrier detection, a comparative study of serum PK and CPK activity was performed in 74 female relatives of patients affected with Duchenne (DMD) and Becker (BMD) muscular dystrophies. For obligate carriers of the DMD gene, 10 of 14 had elevated CPK's, 11 of 14 had elevated PK's and 12 of 14 had abnormal results for either of the two enzymes. Three of 16 mothers of isolated cases had increased serum CPK activity and 6 of 16 had increased PK activity (7 had elevation of at least one enzyme). These preliminary data suggest that the use of PK may enhance the capability to discriminate carriers for these X-linked recessive genes.

Tay-Sachs disease: one-step assay of beta-N-acetylhexosaminidase in serum with a sulphated chromogenic substrate.

A sulphated chromogenic compound, p-nitrophenyl-6-sulpho-2-acetamido-2-deoxy-beta-D-glucopyranoside, which can be hydrolysed enzymatically to p-nitrophenol and the sulphated amino sugar, was used as a substrate for the determination of activity of beta-N-acetylhexosaminidase isoenzymes in human serum. The sera of six Tay-Sachs patients lacking isoenzyme A and heat-inactivated control serum exhibited 6% of the mean normal enzyme activity of 1.32 U/l (1-s range = 1.07-1.57 U/l). In 10 obligate carriers of the Tay-Sachs gene the enzyme activity was 52% (1-s range = 45-60%) of the mean normal value. Therefore, by using the sulphated chromogenic substrate Tay-Sachs disease can be diagnosed enzymatically in a simple one-step procedure, but the 2-s activity ranges of heterozygotes and normals overlap. The assay is not absolutely specific for isoenzyme A of beta-N-acetylhexosaminidase, because the substrate can be hydrolysed to a certain extent by beta-N-acetylhexosaminidase I.