Townes-Brocks syndrome: twenty novel SALL1 mutations in sporadic and familial cases and refinement of the SALL1 hot spot region.

Townes-Brocks syndrome (TBS) is an autosomal dominant malformation syndrome characterized by renal, anal, ear, and thumb anomalies caused by SALL1 mutations. To date, 36 SALL1 mutations have been described in TBS patients. All but three of those, namely p.R276X, p.S372X, and c.1404dupG, have been found only in single families thereby preventing phenotype-genotype correlations. Here we present 20 novel mutations (12 short deletions, five short duplications, three nonsense mutations) in 20 unrelated families. We delineate the phenotypes and report previously unknown ocular manifestations, i.e. congenital cataracts with unilateral microphthalmia. We show that 46 out of the now 56 SALL1 mutations are located between the coding regions for the glutamine-rich domain mediating SALL protein interactions and 65 bp 3' of the coding region for the first double zinc finger domain, narrowing the SALL1 mutational hotspot region to a stretch of 802 bp within exon 2. Of note, only two SALL1 mutations would result in truncated proteins without the glutamine-rich domain, one of which is reported here. The latter is associated with anal, ear, hand, and renal manifestations, indicating that the glutamine-rich domain is not required for typical TBS.

Molecular analysis of the CHD7 gene in CHARGE syndrome: identification of 22 novel mutations and evidence for a low contribution of large CHD7 deletions.

PURPOSE: Autosomal dominant CHARGE syndrome (OMIM no. 214800) is characterized by choanal atresia or cleft lip or palate, ocular colobomas, cardiovascular malformations, retardation of growth, ear anomalies, and deafness, and is caused by mutations in the CHD7 gene. Here, we describe the outcome of a molecular genetic analysis in 18 Finnish and 56 German patients referred for molecular confirmation of the clinical diagnosis of suspected CHARGE syndrome. METHODS: Quantitative real-time polymerase chain reaction or multiplex ligation-dependent probe amplification assays did not reveal deletions in mutation negative cases, suggesting that larger CHD7 deletions are not a major cause of CHARGE syndrome. RESULTS: In this group of 74 patients, we found mutations in 30 cases. 22 mutations were novel, including 11 frameshift, 5 nonsense, 3 splice-site, and 3 missense mutations. One de novo frameshift mutation was found in the last exon and is expected to result in a minimally shortened CHD7 polypeptide. Because the mutation is associated with a typical CHARGE syndrome phenotype, it may indicate the presence of an as yet unknown functional domain in the very carboxyterminal end of CHD7. CONCLUSIONS: Our mutation detection rate of 40.5% is reflective of screening an unselected sample population referred for CHD7 testing based on suspected clinical diagnosis of CHARGE syndrome and not for having met strict clinical criteria for this disorder.

Expanding the spectrum of TBX5 mutations in Holt-Oram syndrome: detection of two intragenic deletions by quantitative real time PCR, and report of eight novel point mutations.

Mutations in the gene TBX5 cause Holt-Oram syndrome (HOS), an autosomal dominant disorder characterized by anterior (i.e., radial ray) upper limb malformations and congenital heart defects and/or cardiac conduction anomalies. The detection rate for TBX5 mutations in HOS patients has been given as 30-35% in most reports. However, a detection rate of 74% was reported when strict clinical inclusion criteria for HOS were applied prior to TBX5 analysis. Still, in a significant proportion of typical HOS cases no mutation can be found within the TBX5 coding region and flanking intronic sequences. One explanation could be that large but submicroscopic deletions of TBX5 could cause HOS, yet only one such TBX5 deletion has been reported to date. We developed a quantitative Real Time PCR strategy to detect large, submicroscopic deletions in TBX5. Using this assay, we screened a total of 102 TBX5 mutation negative patients and discovered two novel intragenic deletions. One deletion of 7756 bp removes exon 6 and a considerable part of the neighboring intronic sequences, and the other of 3695 bp removes exon 9 with the stop codon and the 3'UTR completely as well as a part of the preceding intron 8. We conclude that quantitative Real Time PCR is a reliable method to detect submicroscopic deletions within TBX5. However, such deletions explain only approximately 2% of the TBX5 mutational spectrum in HOS cases. In addition, we also present eight novel TBX5 mutations (three nonsense, one splice mutation, four short deletions) as detected by direct sequencing in 21 families not previously analyzed for mutations.

SALL1 mutation analysis in Townes-Brocks syndrome: twelve novel mutations and expansion of the phenotype.

Townes-Brocks syndrome is an autosomal dominantly inherited disorder, which comprises multiple birth defects including renal, ear, anal, and limb malformations. TBS has been shown to result from mutations in SALL1, a human gene related to the developmental regulator SAL of Drosophila melanogaster. The SALL1 gene product is a zinc finger protein thought to act as a transcription factor. It contains four highly conserved, evenly distributed C2H2 double zinc finger domains. A single C2H2 motif is attached to the second domain, and at the amino terminus SALL1 contains a C2HC motif. Most mutations causing TBS are clustered in the N-terminal third of the SALL1 coding region and result in the production of truncated proteins containing only one or none of the C2H2 domains and the N-terminal transcriptional repressor domain of SALL1. Twenty-three SALL1 mutations were reported prior to this work, 22 of which are located in exon 2, 5' of the second double zinc finger-encoding region. Here we present 12 novel mutations in SALL1 associated with Townes-Brocks syndrome in 13 unrelated families. These include three nonsense mutations, three short insertions and six short deletions. Thus the number of SALL1 mutations increases to 35. Rare phenotypical features among mutation positive patients include hypothyroidism, vaginal aplasia with bifid uterus, cryptorchidism, bifid scrotum without hypospadia scrotalis, unilateral chorioretinal coloboma with loss of vision, dorsal hypoplasia of the corpus callosum, and umbilical hernia.