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Background: Mutations in human SIX1 gene cause branchiootorenal or branchiootic syndrome. Six1 deficient mice exhibit uni- or bilateral renal hypoplasia or kidney agenesis. Furthermore a lack of Six1 gene in the ureter leads to hydroureter and hydronephrosis. These murine malformations resemble human kidney and urinary tract congenital anomalies (CAKUT), a group of diseases with a diverse anatomical spectrum which includes duplex collecting system as much as urethra kidney and ureteropelvic anomalies. Our study focuses on whether mutations or deletion of this gene may be associated with nonsyndromic CAKUT., Methods: Fifty unrelated patients (13-21 years) with nonsyndromic CAKUT were retrospectively recruited for SIX1 sequence variations analysis, and compared to three subjects without malformative nephrouropathies (controls). SIX1 coding sequence was screened by high resolution melt analysis (HRMA) and by Sanger direct sequencing. A quantitative comparative real-time polymerase chain reaction (PCR) was later performed in order to detect the presence of SIX1 gene deletion., Results: We did not find significant differences in the HRMA melting curves for each of the SIX1 coding exons between patients and controls, as also confirmed by Sanger direct sequencing. Moreover quantitative comparative real-time PCR for SIX1 and data normalization excluded total SIX1 gene deletion in our patients., Conclusions: We did not find sequence variations in SIX1 coding regions or complete gene deletion in our CAKUT population. These results suggest that alterations in these sequences are unlikely to be a major cause of nonsyndromic CAKUT. Nevertheless, further studies are necessary to understand if altered SIX1 expression may play a role in human development of kidney and urinary tract congenital anomalies.

The severe mental retardation and speech deficits associated with 22q13 terminal deletions have been attributed in large part to haploinsufficiency of SHANK3, which maps to all 22q13 terminal deletions, although more proximal genes are assumed to have minor effects. We report two children with interstitial deletions of 22q13 and two copies of SHANK3, but clinical features similar to the terminal 22q13 deletion syndrome, including mental retardation and severe speech delay. Both these interstitial deletions are completely contained within the largest terminal deletion, but do not overlap with the nine smallest terminal deletions. These interstitial deletions indicate that haploinsufficiency for 22q13 genes other than SHANK3 can have major effects on cognitive and language development. However, the relatively mild speech problems and normal cognitive abilities of a parent who transmitted her identical interstitial deletion to her more severely affected son suggests that the phenotype associated with this region may be more variable than terminal deletions and therefore contribute to the relative lack of correlation between clinical severity and size of terminal deletions. The phenotypic similarity between the interstitial deletions and non-overlapping small terminal 22q13 deletions emphasizes the general nonspecificity of the clinical picture of the 22q13 deletion syndrome and the importance of molecular analysis for diagnosis.