Mosaic trisomy 7 in a patient with pigmentary abnormalities.

Somatic chromosomal mosaicism may present as isolated pigmentary abnormalities or multiple congenital anomalies with mental retardation. Pigmentary lesions are visually dramatic and are differentiated based on appearance when the underlying pathogenesis is not known. It is now clear that mosaicism is responsible for the pigmentary findings in hypomelanosis of Ito (HI) and linear and whorled nevoid hypermelanosis (LWH). Both hypopigmentation and hyperpigmentation have been noted in the same individual, and both LWH and HI can be caused by similar chromosomal abnormalities. Both of these conditions exhibit similar systemic involvement. We present a case of LWH associated with mosaic trisomy 7 and review the relevant literature.

Discordance for keratoconus in two pairs of monozygotic twins.

PURPOSE: We present two pairs of monozygotic twins discordant for keratoconus. METHODS: Two pairs of twins, each with one twin with keratoconus, and available family members were examined clinically and with computer-assisted videokeratography. Polymerase chain reaction-based zygosity assays using between nine and 11 unique, anonymous DNA markers were performed on blood obtained from the twins and surviving parents to assess the probability of genetic monozygosity. RESULTS: DNA probes showed a >99% probability that each of the two sets of twins was monozygotic. One twin from each pair had clinically diagnosed keratoconus. The remaining twins were normal by clinical examination and corneal topography. Clinical results for all family members examined were normal except that five of 13 from one family and one of six from the other family demonstrated "suspicious" corneal topography. CONCLUSION: Recent advances in knowledge and understanding of the twinning process suggest that monozygotic twins discordant for keratoconus does not preclude the possibility of a significant genetic component.

Non-mosaic tetrasomy 9p in a liveborn infant with multiple congenital anomalies: case report and comparison with trisomy 9p.

Tetrasomy of the short(p) arm of chromosome 9 has been reported in few cases. Most of these children present with microbrachycephaly, wide forehead, hypertelorism, lowset, malformed ears, beaked noses, and micrognathia. Additional anomalies include short neck, congenital heart disease, genital abnormalities, multiple limb defects, hypotonia, and early death.

Prenatal detection of an inverted X chromosome in a male.

An unusual case of an X chromosome with a pericentric inversion (p11.3q21.3) was detected prenatally in a male fetus. This inversion has not been previously characterized. Although the inverted chromosome was transmitted through the mother, no living males on the maternal side were detected with the aberrant chromosome. Replication studies were performed on cultures of maternal peripheral blood lymphocytes, and it was determined that the inverted X chromosome was early replicating in approximately half of the cells. Following genetic counseling, the pregnancy was continued and a healthy male infant was delivered at term. Cytogenetic analysis of peripheral blood performed in the newborn period confirmed the prenatal findings. The child is developing normally at 3 years of age.

Causal heterogeneity in isolated lissencephaly.

We report clinical, cytogenetic, and molecular studies in 65 patients with isolated lissencephaly sequence (ILS). All had type I lissencephaly of varying severity and a grossly normal cerebellum. Some had additional brain abnormalities. Facial appearance was essentially normal. All had severe to profound mental retardation, seizures, hypotonia that evolved into spasticity, and feeding difficulties. Clinical and laboratory studies demonstrated etiologic heterogeneity. Molecular studies detected microdeletions in chromosome band 17p13.3 in six of 44 patients tested, confirming that deletion of all or part of this "critical region" is the cause of ILS in some cases. There were slightly larger deletions in the same region in a majority of patients with Miller-Dieker syndrome. One patient had an apparently balanced, de novo reciprocal translocation with breakpoints at Xq22 and 2p25. Four sibs from two families had a new, autosomal recessive syndrome of ILS with neonatal death. Other causes supported by clinical observations include autosomal recessive inheritance, intrauterine infection, and intrauterine perfusion failure. Those ILS probands in whom no etiology could be established had 41 sibs of whom three were affected, giving an empiric recurrence risk of 7%.

Evidence for a major gene in familial anencephaly.

A 21-year-old white woman sought counseling after the birth of two consecutive anencephalic male fetuses with complete rachischisis and discordant renal dysplasia. The presence of parental consanguinity prompted reconsideration of recessive inheritance. The segregation ratio from 23 additional consanguineous cases was compared with that observed in 294 presumably nonconsanguineous families previously reported. Using classical segregation analysis, the segregation ratios in the non-sporadic cases were consistent with a major autosomal recessive locus in both populations.