Genomic imbalance in the centromeric 11p15 imprinting center in three families: Further evidence of a role for IC2 as a cause of Russell-Silver syndrome.

Russell-Silver syndrome is a heterogeneous disorder characterized by intrauterine growth retardation, postnatal growth deficiency, characteristic facial appearance, and other variable features. Genetic and epigenetic alterations are identified in about 60% of individuals with Russell-Silver syndrome. Most frequently, Russell-Silver syndrome is caused by altered gene expression on chromosome 11p15 due to loss of methylation at the telomeric imprinting center. To date there have been a handful of isolated clinical reports implicating the centromeric imprinting center 2 in the etiology of Russell-Silver syndrome. Here we report three new families with genomic imbalances, involving imprinting center 2 resulting in gain of methylation at this center and a Russell-Silver syndrome phenotype, including two families with a maternally inherited microduplication and the first pediatric patient with a paternally derived microdeletion. The findings in our families provide additional evidence of a role for imprinting center 2 in the etiology of Russell-Silver syndrome and suggest that imprinting center 2 imprinting abnormalities may be a more common cause of Russell-Silver syndrome than previously recognized. Furthermore, our findings together with previous clinical reports of genomic imbalances involving imprinting center 2 serve to underscore the complexity of the epigenetic regulation of the 11p15 region making it challenging to predict phenotype on the basis of genotype alone. © 2016 Wiley Periodicals, Inc.

Fraternal twins with Aarskog-Scott syndrome due to maternal germline mosaicism.

Aarskog-Scott syndrome is a rare X-linked recessive disorder with characteristic facial, skeletal, and genital abnormalities. We report on Aarskog-Scott syndrome in male dizygotic twins with an identical de novo mutation in FGD1 that resulted from germline mosaicism in the phenotypically normal mother. This is the first report of inheritance by germline mosaicism for the FGD1 gene.

Novel de novo PCDH19 mutations in three unrelated females with epilepsy female restricted mental retardation syndrome.

Epilepsy and Mental Retardation Limited to Females (EFMR) [OMIM 300088] was first described in 1971 [Juberg and Hellman, 1971] in 15 related females with early onset grand mal seizures and mental retardation. Although EFMR demonstrates X-linked inheritance, it follows an unusual pattern by sparing transmitting males and affecting only heterozygous females. In 2008, mutations within the protocadherin 19 (PCDH19) gene were implicated as causative of EFMR [Dibbens et al. (2008); Nat Genet 40:776-781]. The EFMR phenotype is typically characterized by seizure onset in infancy and mild to severe intellectual impairment. Several individuals with EFMR have also been described as having autistic features. We describe three unrelated female individuals, ranging in age from 3 to 19 years, with de novo novel PCDH19 mutations. All three individuals have seizure onset in infancy and require the use of multiple antiepileptic drugs. They also have varying degrees of intellectual impairment along with the presence of autistic features. Although most individuals with EFMR described to date demonstrate this unusual familial X-linked inheritance, our three unrelated females with de novo mutations highlight the importance of testing PCDH19 in females with early onset epilepsy, intellectual impairment, and autistic features, regardless of family history.

Beta-thalassemia intermedia due to compound heterozygosity for two beta-globin gene promoter mutations, including a novel TATA box deletion.

An 8-year-old African-American boy had a clinical history consistent with mild beta-thalassemia intermedia with moderate anemia, microcytosis, reticulocytosis, and splenomegaly. He was asymptomatic and did not require transfusion. At age 4 years, hemoglobin (Hb) electrophoresis showed Hb A = 37.8%, Hb A(2) = 5.0%, and Hb F = 56.1%. At age 8 years, he was diagnosed to be a compound heterozygote for two beta-globin gene promoter mutations, the relatively common nucleotide (nt) -88 C --> T mutation from the cap site, and a novel two-nucleotide (AA) deletion between nt -29 and -26 within the TATA box of the beta-globin gene. His mother and 14-year-old brother were simple heterozygotes for this novel (AA) deletion. Both heterozygotes had normal Hb level, borderline microcytosis, and elevated Hb A(2).

THE Hb S/beta+ -thalassemia phenotype demonstrates that the IVS-I (-2) (A>C) mutation is a mild beta-thalassemia allele.

We report a family in which two siblings are compound heterozygotes for Hb S [beta6(A3)GluVal] and a rare beta-globin mutation [IVS-I (-2) (A>C)]. Both patients had significant levels of Hb A, indicating that the IVS-I (-2) mutation is a relatively mild beta(+)-thalassemia (beta(+)-thal) allele. This mutation, in compound heterozygosity with Hb S, does not necessarily lead to a mild clinical course.

Prenatal diagnosis of hemoglobinopathies in Ontario, Canada.

In 1989, the Province of Ontario established a molecular diagnostic laboratory for carrier detection and prenatal diagnosis of hemoglobinopathies. Over the past 15 years, the laboratory has provided prenatal diagnosis for 672 pregnancies at-risk for severe hemoglobinopathies: 276 (41%) for homozygous beta-thalassemia or hemoglobin (Hb) E/beta-thalassemia, 211 (31%) for homozygous alpha 0-thalassemia (Hb Bart's hydrops fetalis), and/or Hb H disease, and 185 (28%) for various sickling disorders (Hb SS, Hb SC, Hb S/beta-thalassemia). Despite the availability of services for carrier screening, genetic counseling, and prenatal diagnosis, there has been only a modest reduction in the overall incidence of hemoglobinopathies in Ontario.

A T-to-G transversion at nucleotide -567 upstream of HBG2 in a GATA-1 binding motif is associated with elevated hemoglobin F.

Increased fetal hemoglobin (Hb F; alpha(2)gamma(2)) production in adults can ameliorate the clinical severity of sickle cell disease and beta-thalassemia major. Thus, understanding the regulation of gamma-globin gene expression and its silencing in adults has potential therapeutic implications. We studied a father and son in an Iranian-American family who had elevated Hb F levels and found a novel T-to-G transversion at nucleotide (nt) -567 of the HBG2 promoter. This mutation alters a GATA-1 binding motif to a GAGA sequence located within a previously identified silencing element. DNA-protein binding assays showed that the GATA motif of interest is capable of binding GATA-1 transcription factor in vitro and in vivo. Truncation analyses of the HBG2 promoter linked to a luciferase reporter gene revealed a negative regulatory activity present between nt -675 and -526. In addition, the T-to-G mutation at the GATA motif increased the promoter activity by two- to threefold in transiently transfected erythroid cell lines. The binding motif is uniquely conserved in simian primates with a fetal pattern of gamma-globin gene expression. These results suggest that the GATA motif under study has a functional role in silencing gamma-globin gene expression in adults. The T-to-G mutation in this motif disrupts GATA-1 binding and the associated repressor complex, abolishing its silencing effect and resulting in the up-regulation of gamma-globin gene expression in adults.

Two new alpha-thalassemia frameshift mutations.

alpha-Thalassemia (thal) is common all over the world. Most of the mutations encountered are of the deletional type. We now report two frameshift alpha-thal mutations: a novel alpha1-globin gene deletion at codon 62 (GTG -->-TG) found in an African American man, and a second report on an alpha2-globin gene deletion at codon 22 (GGC-->GG -) found in a Hispanic girl.

Sickle cell disease due to compound heterozygosity for Hb S and a novel 7.7-kb beta-globin gene deletion.

A young woman originally from Cape Verde islands presented with mild sickle cell disease. Her blood counts and hemoglobin analysis results initially suggested that she might be either homozygous for the sickle cell hemoglobin (Hb S) with concomitant alpha-thalassemia, or compound heterozygous for Hb S and beta0-thalassemia, deletional deltabeta-thalassemia or hereditary persistence of fetal hemoglobin (HPFH). We utilized a novel polymerase chain reaction (PCR)-based screening technique and found a hitherto unrecognized 7.7-kb deletion, starting from the HBB IVSII to 3' downstream of the beta-globin gene. This diagnostic approach can be applied to decipher other similar deletional mutations. This is the second known deletion that removes the 3'-end but preserves the integrity of the 5'-end of the beta-globin gene. Furthermore, the identification of the deletion allows proper genetic counseling for affected families.