Alice S. Brooks

BBS10 encodes a vertebrate-specific chaperonin-like protein and is a major BBS locus

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous ciliopathy. Although nine BBS genes have been cloned, they explain only 40–50% of the total mutational load. Here we report a major new BBS locus, BBS10, that encodes a previously unknown, rapidly evolving vertebrate-specific chaperonin-like protein. We found BBS10 to be mutated in about 20% of an unselected cohort of families of various ethnic origins, including some families with mutations in other BBS genes, consistent with oligogenic inheritance. In zebrafish, mild suppression of bbs10 exacerbated the phenotypes of other bbs morphants.

Homozygous Nonsense Mutations in KIAA1279 Are Associated with Malformations of the Central and Enteric Nervous Systems

We identified, by homozygosity mapping, a novel locus on 10q21.3-q22.1 for Goldberg-Shprintzen syndrome (GOSHS) in a consanguineous Moroccan family. Phenotypic features of GOSHS in this inbred family included microcephaly and mental retardation, which are both central nervous system defects, as well as Hirschsprung disease, an enteric nervous system defect. Furthermore, since bilateral generalized polymicogyria was diagnosed in all patients in this family, this feature might also be considered a key feature of the syndrome. We demonstrate that homozygous nonsense mutations in KIAA1279 at 10q22.1, encoding a protein with two tetratrico peptide repeats, underlie this syndromic form of Hirschsprung disease and generalized polymicrogyria, establishing the importance of KIAA1279 in both enteric and central nervous system development.

RET and GDNF gene scanning in Hirschsprung patients using two dual denaturing gel systems.

Hirschsprung disease (HSCR) is a congenital disorder characterised by intestinal obstruction due to an absence of intramural ganglia along variable lengths of the intestine. RET is the major gene involved in HSCR. Mutations in the GDNF gene, and encoding one of the RET ligands, either alone or in combination with RET mutations, can also cause HSCR, as can mutations in four other genes (EDN3, EDNRB, ECE1, and SOX10). The rare mutations in the latter four genes, however, are more or less restricted to HSCR associated with specific phenotypes. We have developed a novel comprehensive mutation detection system to analyse all but three amplicons of the RET and GDNF genes, based on denaturing gradient gel electrophoresis. We make use of two urea‐formamide gradients on top of each other, allowing mutation detection over a broad range of melting temperatures. For the three remaining (GC‐rich) PCR fragments we use a combination of DGGE and constant denaturing gel electrophoresis (CDGE). These two dual gel systems substantially facilitate mutation scanning of RET and GDNF, and may also serve as a model to develop mutation detection systems for other disease genes. In a screening of 95 HSCR patients, RET mutations were found in nine out of 17 familial cases (53%), all containing long segment HSCR. In 11 of 78 sporadic cases (14%), none had long segment HSCR. Only one GDNF mutation was found, in a sporadic case. Hum Mutat 15:418–429, 2000.

Kabuki syndrome: a review study of three hundred patients.

The Kabuki (make-up) syndrome identified in 1981 has been reported in more than three hundred patients. Typical findings include mild to moderate mental retardation, fetal pads, cleft palate, and characteristic facies with long palpebral fissures, everted lower lateral eyelids and arched eyebrows. Postnatal growth retardation, skeletal and visceral anomalies are present in a large percentage of patients. We review here the characteristics of this peculiar syndrome in three hundred patients.

Lessons from BWS twins: complex maternal and paternal hypomethylation and a common source of haematopoietic stem cells

The Beckwith–Wiedemann syndrome (BWS) is a growth disorder for which an increased frequency of monozygotic (MZ) twinning has been reported. With few exceptions, these twins are discordant for BWS and for females. Here, we describe the molecular and phenotypic analysis of 12 BWS twins and a triplet; seven twins are MZ, monochorionic and diamniotic, three twins are MZ, dichorionic and diamniotic and three twins are dizygotic. Twelve twins are female. In the majority of the twin pairs (11 of 13), the defect on chromosome 11p15 was hypomethylation of the paternal allele of DMR2. In 5 of 10 twins, there was additional hypomethylation of imprinted loci; in most cases, the loci affected were maternally methylated, but in two cases, hypomethylation of the paternally methylated DLK1 and H19 DMRs was detected, a novel finding in BWS. In buccal swabs of the MZ twins who share a placenta, the defect was present only in the affected twin; comparable hypomethylation in lymphocytes was detected in both the twins. The level of hypomethylation reached levels below 25%. The exchange of blood cells through vascular connections cannot fully explain the degree of hypomethylation found in the blood cell of the non-affected twin. We propose an additional mechanism through which sharing of aberrant methylation patterns in discordant twins, limited to blood cells, might occur. In a BWS-discordant MZ triplet, an intermediate level of demethylation was found in one of the non-affected sibs; this child showed mild signs of BWS. This finding supports the theory that a methylation error proceeds and possibly triggers the twinning process.

Studying the genetics of Hirschsprung's disease: Unraveling an oligogenic disorder

Hirschsprungs disease is characterized by the absence of ganglion cells in the myenteric and submucosal plexuses of the gastrointestinal tract. Genetic dissection was successful as nine genes and four loci for Hirschsprungs disease susceptibility were identified. Different approaches were used to find these loci such as classical linkage in large families, identity by descent mapping in an inbred kindred, candidate gene approaches based on naturally occurring mutant mice models, and finally the use of model‐free linkage and association analyzes. In this study, we review the identification of genes and loci involved in the non‐syndromic common form and syndromic Mendelian forms of Hirschsprungs disease. The majority of the identified genes are related to Mendelian syndromic forms of Hirschsprungs disease. The non‐Mendelian inheritance of sporadic non‐syndromic Hirschsprungs disease proved to be complex; involvement of multiple loci was demonstrated in a multiplicative model. We discuss the practical implications of the elucidation of genes associated with Hirschsprungs disease susceptibility for genetic counseling. Finally, we speculate on possible strategies to identify new genes for Hirschsprungs disease.

Localizing a putative mutation as the major contributor to the development of sporadic Hirschsprung disease to the RET genomic sequence between the promoter region and exon 2

Hirschsprung disease (HSCR), a congenital disorder characterized by intestinal obstruction due to absence of enteric ganglia along variable lengths of the intestinal tract, occurs both in familial and sporadic cases. RET mutations have been found in approximately 50% of the families, but explains only a minority of sporadic cases. This study aims at investigating a possible role of RET in sporadic HSCR patients. Haplotypes of 13 DNA markers, within and flanking RET, have been determined for 117 sporadic HSCR patients and their parents. Strong association was observed for six markers in the 5′ region of RET. The largest distortions in allele transmission were found at the same markers. One single haplotype composed of these six markers was present in 55.6% of patients versus 16.2% of controls. Odds ratios (ORs) revealed a highly increased risk of homozygotes for this haplotype to develop HSCR (OR>20). These results allowed us to conclude that RET plays a crucial role in HSCR even when no RET mutations are found. An unknown functional disease variant(s) with a dosage-dependent effect in HSCR is likely located between the promoter region and exon 2 of RET.

A consanguineous family with Hirschsprung disease, microcephaly, and mental retardation (Goldberg-Shprintzen syndrome)

Hirschsprung disease, mental retardation, microcephaly, and specific craniofacial dysmorphism were observed in three children from a large, consanguineous, Moroccan family. A fourth child showed similar clinical features, with the exception of Hirschsprung disease. The association of these abnormalities in these children represents the Goldberg-Shprintzen syndrome (OMIM 235730).  Mutation scanning of genes potentially involved in Hirschsprung disease, RET, GDNF, EDN3, and EDNRB, showed a sequence variant, Ser305Asn, in exon 4 of the EDNRB gene in the index patient of this family. The Ser305Asn substitution present in two of the four patients and four healthy relatives and absent in one of the remaining two patients illustrates the difficulties in interpreting the presence of mutations in families with Hirschsprung disease. It is unlikely that the EDNRB variant contributes to the phenotype. This consanguineous family might be useful for the identification of a Goldberg-Shprintzen locus.

Novel FOXF1 Mutations in Sporadic and Familial Cases of Alveolar Capillary Dysplasia with Misaligned Pulmonary Veins Imply a Role for its DNA Binding Domain

Alveolar capillary dysplasia with misalignment of pulmonary veins (ACD/MPV) is a rare and lethal developmental disorder of the lung defined by a constellation of characteristic histopathological features. Nonpulmonary anomalies involving organs of gastrointestinal, cardiovascular, and genitourinary systems have been identified in approximately 80% of patients with ACD/MPV. We have collected DNA and pathological samples from more than 90 infants with ACD/MPV and their family members. Since the publication of our initial report of four point mutations and 10 deletions, we have identified an additional 38 novel nonsynonymous mutations of FOXF1 (nine nonsense, seven frameshift, one inframe deletion, 20 missense, and one no stop). This report represents an up to date list of all known FOXF1 mutations to the best of our knowledge. Majority of the cases are sporadic. We report four familial cases of which three show maternal inheritance, consistent with paternal imprinting of the gene. Twenty five mutations (60%) are located within the putative DNA‐binding domain, indicating its plausible role in FOXF1 function. Five mutations map to the second exon. We identified two additional genic and eight genomic deletions upstream to FOXF1. These results corroborate and extend our previous observations and further establish involvement of FOXF1 in ACD/MPV and lung organogenesis.

Studying the genetics of Hirschsprung's disease

Hirschsprungs disease is characterized by the absence of ganglion cells in the myenteric and submucosal plexuses of the gastrointestinal tract. Genetic dissection was successful as nine genes and four loci for Hirschsprungs disease susceptibility were identified. Different approaches were used to find these loci such as classical linkage in large families, identity by descent mapping in an inbred kindred, candidate gene approaches based on naturally occurring mutant mice models, and finally the use of model‐free linkage and association analyzes. In this study, we review the identification of genes and loci involved in the non‐syndromic common form and syndromic Mendelian forms of Hirschsprungs disease. The majority of the identified genes are related to Mendelian syndromic forms of Hirschsprungs disease. The non‐Mendelian inheritance of sporadic non‐syndromic Hirschsprungs disease proved to be complex; involvement of multiple loci was demonstrated in a multiplicative model. We discuss the practical implications of the elucidation of genes associated with Hirschsprungs disease susceptibility for genetic counseling. Finally, we speculate on possible strategies to identify new genes for Hirschsprungs disease.