Inactivating mutations in ESCO2 cause SC phocomelia and Roberts syndrome: no phenotype-genotype correlation.
The rare, autosomal recessive Roberts syndrome (RBS) is characterized by tetraphocomelia, profound growth deficiency of prenatal onset, craniofacial anomalies, microcephaly, and mental deficiency. SC phocomelia (SC) has a milder phenotype, with a lesser degree of limb reduction and with survival to adulthood. Since heterochromatin repulsion (HR) is characteristic for both disorders and is not complemented in somatic-cell hybrids, it has been hypothesized that the disorders are allelic. Recently, mutations in ESCO2 (establishment of cohesion 1 homolog 2) on 8p21.1 have been reported in RBS. To determine whether ESCO2 mutations are also responsible for SC, we studied three families with SC and two families in which variable degrees of limb and craniofacial abnormalities, detected by fetal ultrasound, led to pregnancy terminations. All cases were positive for HR. We identified seven novel mutations in exons 3-8 of ESCO2. In two families, affected individuals were homozygous--for a 5-nucleotide deletion in one family and a splice-site mutation in the other. In three nonconsanguineous families, probands were compound heterozygous for a single-nucleotide insertion or deletion, a nonsense mutation, or a splice-site mutation. Abnormal splice products were characterized at the RNA level. Since only protein-truncating mutations were identified, regardless of clinical severity, we conclude that genotype does not predict phenotype. Having established that RBS and SC are caused by mutations in the same gene, we delineated the clinical phenotype of the tetraphocomelia spectrum that is associated with HR and ESCO2 mutations and differentiated it from other types of phocomelia that are negative for HR.
Schüle
Birgitt
B
Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305-5323, USA.
Oviedo
Angelica
A
Johnston
Kathreen
K
Pai
Shashidhar
S
Francke
Uta
U
D000015:Abnormalities, Multiple / Q000000981:diagnostic imaging / Q000235:genetics; D000123:Acetyltransferases; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics*; D002874:Chromosome Mapping; D002898:Chromosomes, Human, Pair 8; D019465:Craniofacial Abnormalities / Q000000981:diagnostic imaging / Q000235:genetics; D004252:DNA Mutational Analysis; D004480:Ectromelia / Q000000981:diagnostic imaging / Q000235:genetics*; D005091:Exons; D005260:Female; D016368:Frameshift Mutation; D005838:Genotype; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D020125:Mutation, Missense; D010375:Pedigree; D010641:Phenotype; D011247:Pregnancy; D022821:RNA Splice Sites; D011859:Radiography; D012720:Severity of Illness Index; D014463:Ultrasonography
D002868:Chromosomal Proteins, Non-Histone; D022821:RNA Splice Sites; D000123:Acetyltransferases; C500785:ESCO2 protein, human