Pre- and postnatal diagnosis of trisomy 4 mosaicism.

A liveborn girl with 46,XX/47,XX+4 mosaicism is reported for the first time. The diagnosis of true mosaicism was established initially in the assay of cultured amniotic fluid cells, although fetal blood obtained by percutaneous umbilical blood sampling showed a 46,XX chromosome constitution. The liveborn infant had manifestations previously reported in dup(4p) and dup(4q) syndromes. Cells in cord and arterial blood samples also were 46,XX, but cultures of placenta and bilateral forearm skin biopsies showed 46,XX/47,XX,+4 mosaicism. This case illustrates the disadvantage of chromosome analysis from blood alone when tissue-specific mosaicism is present.

Analysis of crossing-over in a family with translocation 9;10 involving a chromosome 9 with a pericentric inversion.

The presence of two markers on chromosome 9, both a balanced reciprocal translocation and an inversion, allows morphologic demonstration of recombination between the normal and rearranged homologues. In the family under discussion 50% of the progeny studied (two of four) received a translocated 9 without the inversion from a parent with a translocated and inverted 9, indicating crossing-over between members of the chromosome 9 pair. Thus the morphology of the chromosomes allows a recombinant event which is normally invisible to be seen cytologically. Theoretically after crossing-over the balanced reciprocal translocation heterozygote results from adjacent-1 segregation and unbalanced derivative chromosome combinations from alternate segregation. Therefore it cannot be assumed that the balanced progeny necessarily result from alternate segregation and the unbalanced from adjacent-1. The prenatal diagnostic studies presented in this report also show that chromosome analysis of other family members is required when the recombination between homologues produces differences in chromosome morphology between parent and fetus.

Acceptance of amniocentesis by low-income patients in an urban hospital.

A study was made of increased accessibility of genetic services to low-income obstetric patients in Atlanta, Georgia. The proportion of black patients averaged 83%. Of 522 patients counseled from August, 1976, through 1978, 157 were offered amniocentesis, and 95 (61%) elected the procedure. For most of the patients (120, or 76%) who were eligible for amniocentesis, age (greater than or equal to 35 years at delivery) was an indication; and of these, only six (5%) had any prior knowledge of genetic risk. During the same time interval, 188 patients over 35 years of age who initiated prenatal care too late for prenatal diagnosis were counseled in the hospital after delivery; 101 (54%) indicated that they would have accepted amniocentesis. The conclusion was that (1) genetic services are acceptable to this socioeconomic group, and (2) accessibility and publicity are needed to promote utilization in this population.

Limitations of amniography in the prenatal diagnosis of spina bifida.

A fetus with an open, noncystic myelomeningocele was detected at the 22nd week of gestation in a woman monitored for advanced maternal age. The lesion could not be demonstrated on amniography. In 13% of published reports amniography failed to detect significant spina bifida lesions. This false-negative rate seems related to the noncystic nature of some neural tube defects at midgestation.

Testing for the Tay-Sachs gene in the Atlanta Jewish population.

In May 1975, three mass screening clinics for the asymptomatic Tay-Sachs carrier were held in Atlanta, Georgia. Ninety percent of the 2,330 adults screened were of Ashkenazi Jewish ancestry. One hundred seventy-six people were identified as possible carriers, 145 returned for retesting, and 74 were diagnosed as carriers. The Tay-Sachs heterozygote frequency estimated from this tested population was 0.043 or 1 in 23. Retesting of all possible carriers and assessment of their first-degree relatives were emphasized as saids in diagnosis of the carrier state. Our results indicated that the hexosaminidase A values in the white celll lysates used for the retest procedure provided a more reliable diagnosis of the carrier state than did enzyme values obtained from screening sera alone. Test results from first-degree relatives in all cases supported the assigned genotype of probands.