Clinical experience has suggested that patients with the contiguous gene syndrome, complex glycerol kinase deficiency (cGKD), will have mental retardation (MR) if they have deletions extending from the GK gene into the DMD gene and/or involving a significant extension telomeric from DAX1.
The increasing use of array-CGH in malformation syndromes with intellectual disability could lead to the description of new contiguous gene syndrome by the analysis of the gene content of the microdeletion and reverse phenotyping.
Genotype-phenotype correlations revealed that patients with CREBBP deletions extending beyond this gene did not always have a more severe phenotype than patients harboring CREBBP point mutations, suggesting that neighboring genes play only a limited role in the etiopathogenesis of CREBBP-centerd contiguous gene syndrome.
This contiguous gene syndrome is reminiscent of Okihiro syndrome and emphasizes the importance of array-CGH as a diagnostic tool in atypical syndromic presentations with intrafamilial variability.
IL1RAPL1 (interleukin-1 receptor accessory protein-like 1) located at Xp21.3-22.1 has repeatedly been shown to be deleted in patients with a contiguous gene syndrome also affecting neighboring genes, in particular DMD (dystrophin), DAX-1 (NR0B1, nuclear receptor subfamily 0, group B, member 1), and GK (glycerol kinase).
In particular, we propose the CELSR1, ATXN10, FBLN1, and UPK3A as candidate genes in the onset of the main clinical features of this contiguous gene syndrome.
In conclusion, we report a novel phenotypic association of Feingold syndrome type 2 and keratoconus, a likely contiguous gene syndrome due to a large genomic deletion on 13q spanning MIR17HG and a still to be identified gene for keratoconus.
Our study determined the deletion breakpoints in two patients with CGS involving CYBB by array comparative genomic hybridization and the following PCR and DNA walking studies.
Further candidate genes are suspected to explain the malformations associated with cerebral anomalies in the hypothesis of a contiguous gene syndrome: SPRY2 in 13q31.1 is implicated in lens cell proliferation and differentiation for congenital cataract; GPC5 in 13q32 is mainly expressed in the mesenchyme of the developing limb bud for upper limb anomalies.
Further candidate genes are suspected to explain the malformations associated with cerebral anomalies in the hypothesis of a contiguous gene syndrome: SPRY2 in 13q31.1 is implicated in lens cell proliferation and differentiation for congenital cataract; GPC5 in 13q32 is mainly expressed in the mesenchyme of the developing limb bud for upper limb anomalies.
Alpha thalassemia retardation associated with chromosome16 (ATR-16 syndrome) is defined as a contiguous gene syndrome resulting from haploinsufficiency of the alpha-globin gene cluster and genes involved in mental retardation (MR).