Experience of chromosomal microarray applied in prenatal and postnatal settings in Hong Kong.

Chromosomal microarray (CMA) is recommended as a first tier investigation for patients with developmental delay (DD), intellectual disability (ID), autistic spectrum disorder (ASD), and multiple congenital anomalies (MCA). It is widely used in the prenatal and postnatal settings for detection of chromosomal aberrations. This is a retrospective review of all array comparative genomic hybridization (aCGH/ array CGH) findings ascertained in two major prenatal and postnatal genetic diagnostic centers in Hong Kong from June 2012 to December 2017. Medical records were reviewed for cases with pathogenic and variants of uncertain clinical significance (VUS). Classification of copy number variants (CNVs) was based on current knowledge and experience by August 2018. The aims of this review are to study the diagnostic yield of array CGH application in prenatal and postnatal settings in Hong Kong and to describe the spectrum of abnormalities found. Prenatal indications included abnormal ultrasound findings, positive Down syndrome screening, abnormal noninvasive prenatal test results, advanced maternal age and family history of chromosomal or genetic abnormalities. Postnatal indications included unexplained DD, ID, ASD, and MCA. A total of 1,261 prenatal subjects and 3,096 postnatal patients were reviewed. The prenatal diagnostic yield of pathogenic CNV and VUS (excluding those detectable by karyotype) was 3.5%. The postnatal diagnostic yield of pathogenic CNV was 15.2%. The detection rates for well-defined microdeletion and microduplication syndromes were 4.6% in prenatal and 6.1% (1 in 16 index patients) in postnatal cases, respectively. Chromosomes 15, 16, and 22 accounted for over 21 and 25% of pathogenic CNVs detected in prenatal and postnatal cohorts, respectively. This review provides the first large scale overview of genomic imbalance of mostly Chinese patients in prenatal and postnatal settings.

First Report of a Novel Deletion Due to εγδß-Thalassemia in a Chinese Family.

A fetus of Chinese descent presented with ultrasound features of anemia at 20 weeks' gestation. Father had low a mean corpuscular volume (MCV) level. Multiplex gap-polymerase chain reaction (gap-PCR) excluded common α-thalassemia (α-thal) deletions and mutations and PCR sequencing of the α1- and α2-globin genes were negative. The fetus had a normal karyotype. Array comparative genomic hybridization (aCGH) showed a single copy loss of 189.87 kb in chromosome 11p15.4, involving the whole ß-globin gene cluster, inherited from the father. Multiplex ligation-dependent probe amplification (MLPA) confirmed the deletion included the ε-globin gene, confirming the diagnosis of heterozygous (εγδß)0-thalassemia [(εγδß)0-thal], also inherited from the father. The fetus had a worsening anemic condition in utero and required a transfusion at 26 weeks' gestation, raising the hemoglobin (Hb) level from 5.3 to 12.6g/dL. A cesarean-section was subsequently performed at 32 weeks' gestation because of reduced fetal movements, and a 1650g baby girl with good Apgar scores was delivered. Hemoglobin at birth was 12.8g/dL, gradually dropping to 6.8 g/dL, requiring three neonatal transfusions. Her condition gradually stabilized after 2 months with Hb stable at 8.0 g/dL. Family screening by MLPA showed that the paternal grandmother carried the same deletion. The deletion in this case is distinct and is the reported first case. The deletion transmitted across three successive generations with great phenotypic variation. The final adult phenotype of (εγδß)0-thal is usually mild, therefore, with accurate prenatal diagnosis this condition is salvageable by in utero and early neonatal transfusions, preventing adverse pregnancy and neonatal outcomes.

A Fetus with Hb Bart's Disease Due to Maternal Uniparental Disomy for Chromosome 16.

We here report an unusual case of Hb Bart's (γ4) disease. Thalassemia screening of a couple showed that the wife was an α(0)-thalassemia (α(0)-thal) carrier and her husband's mean corpuscular volume (MCV) was normal. Chorionic villus sampling (CVS) was performed at 13 weeks' gestation for positive Down syndrome screening and chromosomal study of the cultured CVS showed a normal karyotype. Ultrasound examination at 22 weeks' gestation showed fetal cardiomegaly and raised middle cerebral artery peak systolic velocity. Cordocentesis confirmed fetal anemia and showed Hb Bart's disease. Multiplex gap-polymerase chain reaction (gap-PCR) for α-thal deletions on DNA extracted from the CVS showed the presence of a homozygous α(0)-thal - -(SEA) (Southeast Asian) deletion. The husband was found to be a carrier of the α(+)-thal -α(3.7) (rightward) deletion. Non paternity was excluded by fluorescent PCR using short tandem repeat (STR) markers on chromosomes 13, 18 and 21. A de novo terminal deletion of chromosome 16 was excluded by array comparative genomic hybridization (aCGH). Detection of uniparental disomy (UPD), using STR markers on chromosome 16 showed maternal uniparental isodisomy from 16pter to 16p13.2, and uniparental heterodisomy from 16p13.13 to 16qter.

An Unusual Hydrops Fetalis Associated with Compound Heterozygosity for Krüppel-like Factor 1 mutations.

Hydrops fetalis is commonly due to Hb Bart's (γ4) disease in South East Asia. Here, we report an unusual case of hydrops fetalis due to congenital dyserythropoietic anemia (CDA) associated with compound heterozygosity for Krüppel-like factor 1 (KLF1) gene mutations. Fetal cardiomegaly was first detected on routine mid-trimester scan in a pregnant woman with normal mean corpuscular volume (MCV) and Rhesus positive status. The fetus subsequently developed hydrops fetalis, and cordocentesis showed severe fetal anemia with a hemoglobin (Hb) level of 3.4 g/dL. Common causes of fetal anemia including Hb Bart's disease, parvovirus infection, and red cell antibodies were excluded. In view of the marked increase in erythroblasts at various stages of erythropoiesis, the diagnosis of CDA was suspected. We screened the couple for previously reported KLF1 gene mutations, showing that the mother was heterozygous for the c.525_526insCGGCGCC, p.Gly176Argfs*179 mutation, and her husband heterozygous for c.1012C>A, p.Pro338Thr mutation. The fetus was a compound heterozygote for these two KLF1 mutations. After counseling, repeated intrauterine transfusions were given at 27, 29, and 34 weeks' gestation; the hydrops fetalis was resolved. The baby was delivered at 34 weeks' gestation and required monthly blood transfusions but was otherwise thriving. Bone marrow aspiration at 10 months of age showed the features of ineffective erythropoiesis, compatible with CDA. In conclusion, hydrops fetalis can rarely be due to CDA associated with a compound heterozygous mutation for KLF1 gene mutations, and be managed by repeated intrauterine transfusions. Our present report adds to the wide clinical spectrum of KLF1 mutations.