Molecular analysis of SALL1 mutations in Townes-Brocks syndrome

Townes-Brocks syndrome (TBS) is an autosomal dominantly inherited malformation syndrome characterized by anal, renal, limb, and ear anomalies. Recently, we showed that mutations in the putative zinc finger transcription factor gene SALL1 cause TBS. To determine the spectrum of SALL1 mutations and to investigate the genotype-phenotype correlations in TBS, we examined 23 additional families with TBS or similar phenotypes for SALL1 mutations. In 9 of these families mutations were identified. None of the mutations has previously been described. Two of these mutations are nonsense mutations, one of which occurred in three unrelated families. Five of the mutations are short deletions. All of the mutations are located 5' of the first double zinc finger (DZF) encoding region and are therefore predicted to result in putative prematurely terminated proteins lacking all DZF domains. This suggests that only SALL1 mutations that remove the DZF domains result in TBS. We also present evidence that in rare cases SALL1 mutations can lead to phenotypes similar to Goldenhar syndrome. However, phenotypic differences in TBS do not seem to depend on the site of mutation.

Mutations in the SALL1 putative transcription factor gene cause Townes-Brocks syndrome

Townes-Brocks syndrome (TBS, OMIM #107480) is a rare autosomal-dominant malformation syndrome with a combination of anal, renal, limb and ear anomalies. Cytogenetic findings suggested that the gene mutated in TBS maps to chromosome 16q12.1, where SALL1 (previously known as HSAL1), a human homologue of spalt (sal), is located. SAL is a developmental regulator in Drosophila melanogaster and is conserved throughout evolution. No phenotype has yet been attributed to mutations in vertebrate sal-like genes. The expression patterns of sal-like genes in mouse, Xenopus and the fish Medaka, and the finding that Medaka sal is regulated by Sonic hedgehog (Shh; ref. 11), prompted us to examine SALL1 as a TBS candidate gene. Here we demonstrate that SALL1 mutations cause TBS in a family with vertical transmission of TBS and in an unrelated family with a sporadic case of TBS. Both mutations are predicted to result in a prematurely terminated SALL1 protein lacking all putative DNA binding domains. TBS therefore represents another human developmental disorder caused by mutations in a putative C2H2 zinc-finger transcription factor.

Isolation, characterization, and organ-specific expression of two novel human zinc finger genes related to the Drosophila gene spalt

The region-specific homeotic gene spalt (sal) of Drosophila specifies head and tail as opposed to trunk segments. During later stages of ontogenesis, sal is also expressed and required in a small number of tissues and organs in the developing embryo. sal encodes a zinc finger protein of unusual but characteristic structure. We made use of these unique features to isolate sal-like genes from humans. Here we report the isolation and molecular characterization of two sal-like transcription units, termed Hsal1 and Hsal2, which are located on chromosomes 16q12.1 and 14q11.1-q12.1, respectively. Their transcripts are expressed in a limited number of adult organs, including the brain. While Hsal2 is evenly expressed in different brain areas, Hsal1 transcripts preferentially accumulate in the corpus callosum and the substantia nigra. In the fetal brain, transcripts of both genes were detected in neurons. The arrangement of sal-like zinc finger domains and their high degree of sequence similarity suggest a novel and conserved subfamily of human zinc finger transcription factors that is closely related to the Drosophila gene product encoded by the gene sal.