MID1 mutation screening in a large cohort of Opitz G/BBB syndrome patients: twenty-nine novel mutations identified

Abstract

Opitz G/BBB Syndrome (OS) is a multiple congenital anomaly disorder characterized by defects along the body midline. The disease is characterized by variable expressivity of signs that include hypertelorism, cleft lip and/or palate, laryngo-tracheo-esophageal abnormalities, cardiac defects, and hypospadias. OS patients also present with mental retardation and brain anatomical abnormalities. An autosomal dominant form mapping to chromosome 22 and an X-linked form of OS are known. The gene responsible for the Xlinked form of OS, MID1, codes for a member of the Tripartite Motif family of E3 ubiquitin ligases. Here we report 29 novel mutations in 29 unrelated patients of a cohort of 140 male OS cases. These mutations are found in both familial and sporadic cases. They are scattered along the entire length of the gene and are represented by missense and nonsense mutations, insertions and deletions causing frame shift mutations, and deletion of either single exons or the entire gene. The variety of the mutations found confirms that loss-of-function is the mechanism underlying the OS phenotype. Moreover, the low percentage of MID1-mutated OS patients, 47% of the familial and 13% of the sporadic cases, suggests a wider genetic heterogeneity underlying the OS phenotype. © 2007 Wiley-Liss, Inc. KEY WORDS: X-linked Opitz syndrome; MID1; midline defects INTRODUCTIONOpitz G/BBB Syndrome (OS; MIM# 300000) is characterized by multiple congenital midline structure anomalies (Opitz, et al., 1969a;Opitz, et al., 1969b laryngo-tracheo-esophageal (LTE) abnormalities; cardiac and anal defects and hypospadias (De Falco, et al., 2003;Robin, et al., 1996). OS patients often show mental retardation and brain anatomical midline defects (De Falco, et al., 2003;Pinson, et al., 2004). OS is genetically heterogeneous with an autosomal dominant and an X-linked form (Robin, et al., 1995). The autosomal dominant form is linked to a large region of 22q11.2 but the gene(s) responsible has not been identified yet (Robin, et al., 1995). Conversely, the gene implicated in the X-linked form of OS, MID1, has been identified on the short arm of the X chromosome (Xp22.3) (Quaderi, et al., 1997). The MID1 gene encodes a member of the Tripartite Motif family (Meroni and Diez-Roux, 2005;Reymond, et al., 2001). MID1 acts as an E3 ubiquitin ligase associated to the microtubules and is implicated in the control of Phosphatase 2A protein levels Schweiger, et al., 1999;Short, et al., 2002;Trockenbacher, et al., 2001). Approximately 40 mutations have been found along the entire length of the MID1 gene in both sporadic and familial cases of OS (Cox, et al., 2000;De Falco, et al., 2003;Gaudenz, et al., 1998;Mnayer, et al., 2006;Pinson, et al., 2004;So, et al., 2005;. The expressivity of the OS symptoms is highly variable and analysis of MID1-mutated patients highlighted the presence of clinical manifestations present in almost all patients (hypertelorism, LTE defects and hypospadias) and other less frequent signs such as cleft lip and/or palate, cardiac and ana...

MID1 mutations in patients with X-linked Opitz G/BBB syndrome

“…Consistently, in the five cases with de novo mutations, the mothers do not have hypertelorism [Cox et al, 2000;Ferrentino et al, 2007]. Small percentages of the female carriers, though, show more severe signs, such as additional OS facial features (anteverted nares, severe short nose, short uvula, high arched palate, micrognathia); tracheoesophageal cleft or esophageal stenosis; anal malformations [Brooks et al, 1992;Pinson et al, 2004;Shaw et al, 2006;So et al, 2005;Winter et al, 2003] (our unpublished results).…”

“…To date, 79 OS male index cases have been published that carry mutations in the MID1 gene [Cho et al, 2006;Cox et al, 2000;De Falco et al, 2003;Ferrentino et al, 2007;Gaudenz et al, 1998;Mnayer et al, 2006;Pinson et al, 2004;Quaderi et al, 1997;Schweiger et al, 1999;Shaw et al, 2006;So et al, 2005;Winter et al, 2003] and three additional OS patients are reported here [Tania Attié-Bitach, personal communication; and our unpublished results] for a total of 82 OS index cases who carry mutations in the MID1 gene. Table 1 lists all the mutations found in the MID1 gene, their position and their putative effect on the protein product or on the transcript.…”

“…Duplicating insertion mutations are described as duplications. Two of the mutations reported have been revised and the correct mutations are: c.388G4A; p.Ala130Thr (and not p.Ala130Ser) and c.389C4T (and not c.389A4T); p.Ala130Val [Ferrentino et al, 2007].…”

“…OS patients usually present with characteristic facial anomalies, including hypertelorism/telecanthus and clefts of lip and/or palate (CL/P), laryngo-tracheo-esophageal (LTE) abnormalities, congenital heart and anal defects, and hypospadias [Cox et al, 2000;De Falco et al, 2003;Ferrentino et al, 2007;Gaudenz et al, 1998;Mnayer et al, 2006;Pinson et al, 2004;Robin et al, 1996;So et al, 2005;Winter et al, 2003]. Developmental delay and mental retardation (MR) have also been documented [De Falco et al, 2003;Pinson et al, 2004].…”

Hypospadias associated with hypertelorism, the mildest phenotype of Opitz syndrome

“…This mutation has been reported before in one OS patient. 21 The mutated protein lacks the whole C-terminus portion and a previous study has indicated that the C-terminus portion maybe have an important role in the association between MID1 and the microtubular apparatus. 22 A microtubule co-assembly assay revealed that, the MID1 protein from OS fetal fibroblasts with the mutation in C-terminal exon lacks microtubule-binding ability.…”