A case of partial trisomy of chromosome 8p associated with autism.

We report on a case of a 6-year-old female with partial trisomy 8p(21-23) associated with autism, mild dysmorphic features, and moderate learning disability. Although mental retardation is a common finding in patients with mosaic trisomy 8 or partial trisomy of various regions of chromosome 8, only two cases associated with autism have been reported so far. Also, in our case clinical manifestations were mild compared to other patients with duplication of the same region of chromosome 8. Although there has been no strong evidence for linkage on chromosome 8 in any of the genome-wide linkage studies so far, the possibility that this segment includes genes involved in the etiology of autism should be further explored.

Maternal uniparental isodisomy 20 in a foetus with trisomy 20 mosaicism: clinical, cytogenetic and molecular analysis.

The clinical significance of trisomy 20 mosaicism detected prenatally remains uncertain due to the rarity of liveborn cases with inconsistent clinical findings, and lack of long-term follow-up and outcome. We describe a case of true trisomy 20 mosaicism in a liveborn girl with maternal uniparental isodisomy of chromosome 20 in the diploid blood cells. Trisomy 20 mosaicism was originally detected in amniotic fluid (98%) and was confirmed in the term placenta (100%), as well as in the blood (10%) and urine sediment (100%) of the neonate. There was intrauterine and postnatal growth retardation, but otherwise the newborn manifested no gross abnormalities. At 9 months of age moderate psychomotor retardation, central hypotonia with peripheral hypertonia, numerous minor morphogenetic variants, marked kyphosis, and extensive Mongolian spot were observed. To our knowledge this represents the first case of trisomy 20 mosaicism detected prenatally and confirmed in different tissues of the newborn, where uniparental disomy was demonstrated in the diploid cell line. The clinical and laboratory findings in our patient are compared with those of five previously reported cases of UPD20, suggesting that maternal UPD20 might be associated with a characteristic phenotype.

Prevalence of GJB2 mutations in prelingual deafness in the Greek population.

OBJECTIVE: Mutations in the gene encoding the gap junction protein connexin 26 (GJB2) have been shown as a major contributor to prelingual, sensorineural, nonsyndromic, recessive deafness. One specific mutation, 35delG, has accounted for the majority of the mutations detected in the GJB2 gene in Caucasian populations. The aim of our study was to determine the prevalence and spectrum of GJB2 mutations in prelingual deafness in the Greek population. METHODS: In a collaboration with the major referral centers for childhood deafness in Greece, patients were examined by an extensive questionnaire to exclude syndromic forms and environmental causes of deafness and by allele-specific polymerase chain reaction (PCR) for the detection of the 35delG mutation. Patients heterozygous for the 35delG mutation were further analyzed by direct genomic sequencing of the coding region of the GJB2 gene. RESULTS: The 35delG mutation was found in 42.2% of the chromosomes in 45 familial cases of prelingual, nonsyndromic deafness (18 homozygotes and 2 heterozygotes) and in 30.6% of the chromosomes in 165 sporadic cases (45 homozygotes and 11 heterozygotes). Direct genomic sequencing in heterozygous patients revealed the L90P (2 alleles), W24X (2 alleles), R184P (2 alleles), and 291insA (1 allele) mutations. CONCLUSION: Mutations in the GJB2 gene are responsible for about one third of prelingual, sensorineural, nonsyndromic deafness in the Greek population, and allele-specific PCR is an easy screening method for the common 35delG mutation.

Double supernumerary isodicentric chromosomes derived from 15 resulting in partial hexasomy.

We report two unrelated patients each with two supernumerary marker chromosomes (SMCs) derived from chromosome 15, and thus resulting in partial hexasomy. Hexasomy in the one case (family 1) was diagnosed at prenatal diagnosis and did not include the Prader-Willi/Angelman critical region (PWACR). The double SMCs were also found in the mother, the pregnancy continued to term, and an apparently phenotypically normal child was born. This represents the first report of transmission of double SMCs from mother to child. In the second case (family 2), the hexasomy did include the PWACR and was de novo in origin. This patient manifested severe psychomotor retardation, clefting of the soft palate, hypotonia, seizure-like episodes, and other phenotypic features. The aberrant phenotype is attributable to the hexasomy for the PWACR gene loci. The normal homologs of chromosome 15 proved to be biparental in origin while the two SMCs appeared maternal.