Alagille syndrome (AGS) is an autosomal dominant disorder characterized by five major symptoms: cholestasis, vertebral deformity, heart malformations, ocular defects and peculiar facial appearance. The previously described Jagged1 (JAG1) gene on chromosome 20p12 has been identified as being responsible for AGS. JAG1 encodes a transmembrane protein acting as ligand for the evolutionarily conserved Notch signaling pathway. Here we report 36 novel mutations in the JAG1 gene. We identified 12 novel deletions, 4 insertions, 8 missense, 7 nonsense and 5 splice site mutations. All mutations map to the sequence encoding the extracellular part of the Jagged1 protein. The mutations spread over the entire gene with slightly increased rates in exons 2 to 6 and exon 23 and 24. Eight novel missense mutations map to the Delta-Serrate-Lag2 (DSL) domain and adjacent sequences which are important for ligand-receptor interaction. Inheritance was determined in 27 families. Sixteen mutations (55%) were de novo and eleven mutations (45%) were transmitted. Altogether 226 different JAG1 mutations have been described in association with AGS, including our novel 36 mutations. AGS variants are spread over the entire gene with only a few mutations in exon 26. A relatively high number of mutations are clustered in exons 2 to 6. This sequence region shows high interspecies conservation and encodes the Notch receptor-binding region (DSL domain).

The Alagille syndrome (AGS), a congenital disorder affecting liver, heart, skeleton and eye in association with a typical face, is an autosomal dominant disease with nearly complete penetrance and variable expression. AGS is caused by mutations in the developmentally important JAG1 gene. In our mutation screening, where 61 mutations in JAG1 were detected, we identified five cases where mosaicism is present. Our results point to a significant frequency of mosaicism for JAG1 mutations in AGS of more than 8.2%. Because mosaicism may be associated with a very mild phenotype, the appropriate diagnosis of AGS and consequently the determination of the recurrence risk can be complicated.

Mowat-Wilson syndrome (MWS) is a rare mental retardation-multiple congenital anomalies syndrome associated with typical facial dysmorphism. Patients can show a variety of other anomalies like short stature, microcephaly, Hirschsprung disease, malformations of the brain, seizures, congenital heart defects and urogenital anomalies. Mutations leading to haploinsufficiency of the ZFHX1B gene have been described as the underlying cause of this condition. We report on the clinical findings in a 2(1/2)-year-old boy with some aspects out of the MWS-spectrum in addition to unusual anomalies and a novel missense mutation in the ZFHX1B gene.

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We report on an adult male with Klinefelter phenotype and an isodicentric Y chromosome (47,XX,+idic(Y)(q12)), a combination which has to the best of our knowledge not been reported before. The patient was hospitalized in forensic psychiatry because of repeated delinquency, aggressive, aberrant and inappropriate behavior, and borderline intelligence. Molecular cytogenetic studies (FISH) showed that the SRY gene was present on both ends of the idicY, while there was only one signal for the Yq subtelomere probe. Molecular investigations by multiplex PCR, using STS markers covering the short and long arm of the Y chromosome did not indicate a deletion of Y chromosomal material. Molecular investigations of STR markers located on Xp22.3 and Xq28 indicated paternal origin of the additional X chromosome and an error in paternal meiosis I. Results of FISH analysis and molecular investigations are compatible with a phenotype as described for individuals with a 48,XXYY karyotype and support the findings that isodicentric Y chromosomes are frequently accompanied by other sex chromosomal abnormalities.

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