Ventricular Noncompaction and Absent Thumbs in a Newborn With Tetrasomy 5q35.2-5q35.3: An Association With Hunter-McAlpine Syndrome?

Division of Human Genetics, Cincinnati Children's Hospital Medical Center, Ohio, USA.
American Journal of Medical Genetics Part A (Impact Factor: 2.16). 06/2011; 155A(6):1409-13. DOI: 10.1002/ajmg.a.33997
Source: PubMed


We report on an infant with tetrasomy of 5q35.2-5q35.3, an interstitial triplication on one chromosome and normal complement on the other. The patient has some features of Hunter-McAlpine syndrome including intrauterine growth retardation (IUGR), almond-shaped eyes, epicanthal folds, and downturned mouth with thin vermillion of the upper lip. In addition, left ventricular noncompaction and absent thumbs were identified, which have never been described in Hunter-McAlpine syndrome. This chromosome abnormality is distinct from those previously reported. Within this region of tetrasomy is MSX2, a highly conserved homeobox containing gene. Increased copies of MSX2 have been previously associated with craniosynostosis. Our patient's only skeletal defect is absent thumbs, also potentially related to increased dosage of MSX2 which is important for limb formation. In addition, MSX2 is expressed in the developing heart and overexpression of this gene may disrupt the co-regulation of other cardiac genes in this region, namely CSX1.

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    • "hypothyroidism) or even unique findings such as bilateral radial agenesis with absent thumbs, bilateral ulnar hypoplasia, abnormal biliary vesicle, and unilateral choroidal and retinal coloboma. Interestingly, absent thumbs were reported so far only in a single patient with an atypical copy number variation (CNV) on 5q, which was the interstitial triplication of the distal 5q segment encompassing MSX2 (6.56 Mb, coordinates according to HG18: 173897858–180456069). Since absent thumbs were never noted in cases with a distal 5q duplication, the authors hypothesized that the relatively severe limb malformation was due to the increased dosage of 5q copies [9]. Although caused solely by a pure duplication, the skeletal phenotype in our patient was more severe and involved bilateral radial aplasia with completely absent Ist digital rays (thumbs and Ist metacarpals), and ulnar hypoplasia with bowing. "
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    ABSTRACT: Background A partial duplication of the distal long arm of chromosome 5 (5q35-- > qter) is known to be associated with a distinct phenotype referred to as Hunter-McAlpine syndrome. Clinical spectrum of this disorder mainly consists of mental retardation, microcephaly, short stature, skeletal anomalies, and craniofacial dysmorphism featuring flat facies, micrognathia, large, low-set dysplastic ears, hypertelorism, almond-shaped, down-slanted palpebral fissures, epicanthal folds, small nose, long philtrum, small mouth, and thin upper lip. Less frequent remarkable findings include craniosynostosis, heart defect, hypoplastic phalanges, preaxial polydactyly, hypospadias, cryptorchidism, and inguinal hernia. In most patients with a partial duplication of 5q the aberration occurred due to an inherited unbalanced translocation, therefore the phenotype was not reflective of pure trisomy 5q. Case presentation We report on a 9.5-year-old boy with some feature of Hunter-McAlpine syndrome including short stature, complex heart defect (dextrocardia, dextroversion, PFO), bilateral cryptorchidism, hypothyroidism, and craniofacial dysmorphism. Additionally, bilateral radial agenesis with complete absence of Ist digital rays, ulnar hypoplasia with bowing, choroidal and retinal coloboma, abnormal biliary vesicle were identified, which have never been noted in 5q trisomy patients. Karyotype analysis, sequencing and MLPA for TBX5 and SALL4 genes were unremarkable. Array comparative genomic hybridization detected a duplication on 5q35.2-5q35.3, resulting from a de novo chromosomal rearrangement. Our proband carried the smallest of all previously reported pure distal 5q trisomies encompassing terminal 5.4-5.6 Mb and presented with the most severe limb malformation attributed to the increased number of distal 5q copies. Conclusions We postulate that a terminal distal trisomy of 5q35.2-5q35.3, which maps 1.1 Mb telomeric to the MSX2 gene is causative for both radial agenesis and complex heart defect in our proband. A potential candidate gene causative for limb malformation in our proband could be FGFR4, which maps relatively in the closest position to the chromosomal breakage site (about 1.3 Mb) from all known 5q duplications. Since the limb malformation as well as the underlying genetic defect are distinct from other 5q trisomy patient we propose that a position effect resulting in altered long-range regulation of the FGFR4 (alternatively MSX2) may be responsible for the limb malformation in our proband.
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