High-resolution SNP microarray investigation of copy number variations on chromosome 18 in a control cohort.

Copy number variations (CNVs) as described in the healthy population are purported to contribute significantly to genetic heterogeneity. Recent studies have described CNVs using lymphoblastoid cell lines or by application of specifically developed algorithms to interrogate previously described data. However, the full extent of CNVs remains unclear. Using high-density SNP array, we have undertaken a comprehensive investigation of chromosome 18 for CNV discovery and characterisation of distribution and association with chromosome architecture. We identified 399 CNVs, of which loss represents 98%, 58% are less than 2.5 kb in size and 71% are intergenic. Intronic deletions account for the majority of copy number changes with gene involvement. Furthermore, one-third of CNVs do not have putative breakpoints within repetitive sequences. We conclude that replicative processes, mediated either by repetitive elements or microhomology, account for the majority of CNVs in the healthy population. Genomic instability involving the formation of a non-B structure is demonstrated in one region.

Hirschsprung disease, microcephaly, mental retardation, and characteristic facial features: delineation of a new syndrome and identification of a locus at chromosome 2q22-q23.

We have identified six children with a distinctive facial phenotype in association with mental retardation (MR), microcephaly, and short stature, four of whom presented with Hirschsprung (HSCR) disease in the neonatal period. HSCR was diagnosed in a further child at the age of 3 years after investigation for severe chronic constipation and another child, identified as sharing the same facial phenotype, had chronic constipation, but did not have HSCR. One of our patients has an interstitial deletion of chromosome 2, del(2)(q21q23). These children strongly resemble the patient reported by Lurie et al with HSCR and dysmorphic features associated with del(2)(q22q23). All patients have been isolated cases, suggesting a contiguous gene syndrome or a dominant single gene disorder involving a locus for HSCR located at 2q22-q23. Review of published reports suggests that there is significant phenotypic and genetic heterogeneity within the group of patients with HSCR, MR, and microcephaly. In particular, our patients appear to have a separate disorder from Goldberg-Shprintzen syndrome, for which autosomal recessive inheritance has been proposed because of sib recurrence and consanguinity in some families.

Trisomy (1q)(q42----qter): confirmation of a syndrome.

This paper describes for the first time the clinical findings in a case of pure trisomy (1q)(q42----qter). Eight cases involving this trisomy have been reported previously, but these were complicated by additional chromosomal changes, and hence the assignation of a discrete phenotype remained doubtful. The clinical abnormalities reported here, most of which were included amongst others in the previous reports of trisomy (1q)(q42----qter), provide the basis for characterisation of this condition as a syndrome. These changes comprised macrocephaly, prominent forehead, micrognathia, large fontanelle, flat nasal bridge, low-set ears, facial capillary naevi, cardiac defect and small size for gestational age.

A case report of a de novo tandem duplication (5p) (p14----pter).

The case described in this paper represents on the basis of cytogenetic evidence, the first reported example of a de novo tandem dup (5p)(p14----pter). Clinical changes were minimal, unlike previously described cases in which more complex structural chromosomal changes were involved and a phenotype was provisionally attributed to dup (5p)(p14----pter). The duplicated segment of minimal effect identified in this case involved more than five eighths of 5p. It is proposed that there is a localised critical segment elsewhere on the short arm of chromosome 5 (p11-p13), which when duplicated is of greater significance in terms of clinical effects.