Ross had only some of the symptoms associated with chromosome 18 deficiencies, including speech delay and farsightedness. Other children have autism, cleft palate, hearing disabilities, physical and mental developmental delay, facial and limb deformities or combinations of these. Speech delay is common in all cases. There is no known cause and no cure, Mrs. Traa said. The 18th chromosome pair is one of 23 swimming in the nucleus of each human cell, carrying worlds of genetic information.
Most chromosome anomalies result in the baby's miscarriage.
Among the few survivable anomalies are Down syndrome, an extra copy of the 21st chromosome, and Fragile X syndrome, repeated genes in the XX or XY chromosome. Chromosome 18 abnormalities are the third most common, consisting of either an extra copy of the chromosome, missing pieces on either strand in the pair, or a strand joined in a circle, with lost genetic material. It appears that the more material missing from the genetic strand, the more severe the difficulties, said Mrs. Traa. The Traas' geneticist referred the couple to the National Organization of Rare Diseases. The Traas discovered a support network of about 1,000 families.