This retrospective study analysed a case series of subjects with citrin deficiency, and aims to present the molecular and clinical characterization of this disease in the Hong Kong Chinese population for the first time. Data from medical records of eighteen patients with citrin deficiency (years 2006-2015) were retrieved. Demographic data, biochemical parameters, radiological results, genetic testing results, management, and clinical outcome were collected and analysed. Eighteen patients with diagnosis of citrin deficiency were recruited. All 18 patients carried at least one common pathogenic variant c.852_855delTATG in SLC25A13. Prolonged jaundice (neonatal intrahepatic cholestasis caused by citrin deficiency, NICCD) was the most common presenting symptom, in conjunction with elevated plasma citrulline, threonine, alkaline phosphatase, and alpha-fetoprotein levels. The abnormal biochemical parameters including liver derangement returned to normal range in most of the cases by 6 months of age after the introduction of a lactose-free formula. There were a few cases with atypical presentations. Two subjects did not present with NICCD, and were subsequently diagnosed later in life after their siblings presented with symptoms of citrin deficiency at one month of age and subsequently received a molecular diagnosis. One patient with citrin deficiency also exhibited multiple liver hemangioendotheliomas, which subsided gradually after introduction of a lactose-free formula. Only one patient from this cohort was offered expanded metabolic screening at birth. She was not ascertained by conducted newborn screening and was diagnosed upon presentation with cholestatic jaundice by 1 month of age. This is the first report of the clinical and molecular characterization of a large cohort of patients with citrin deficiency in Hong Kong. The presentation of this cohort of patients expands the clinical phenotypic spectrum of NICCD. Benign liver tumors such as hemangioendotheliomas may be associated with citrin deficiency in addition to the well-known association with hepatocellular carcinoma. Citrin deficiency may manifest in later infancy period with an NICCD-like phenotype. Furthermore, this condition is not always ascertained by expanded newborn metabolic screening testing.

Demands for expanded carrier screening (ECS) are growing and ECS is becoming an important part of obstetrics practice and reproductive planning. The aim of this study is to evaluate the feasibility of a small-size ECS panel in clinical implementation and investigate Chinese couples’ attitudes towards ECS. An ECS panel containing 11 recessive conditions was offered to Chinese pregnant women below 16 gestational weeks. Sequential testing of their partners was recommended for women with a positive carrier status. The reproductive decision and pregnancy outcome were surveyed for at-risk couples. A total of 1321 women performed ECS successfully and the overall carrier rate was 19.23%. The estimated at-risk couple rate was 0.83%. Sequential testing was performed in less than half of male partners. Eight at-risk couples were identified and four of them performed prenatal diagnosis. Our study demonstrated that a small-size ECS panel could yield comparable clinical value to a larger-size panel when the carrier rate of the individual condition is equal or greater than 1%. In addition, more than half of male partners whose wives were carriers declined any types of sequential testing possibly due to a lack of awareness and knowledge of genetic disorders. Genetic education is warranted for the better implementation of ECS.

Newborn screening (NBS) is an important public health program that aims to identify pre-symptomatic healthy babies that will develop significant disease if left undiagnosed and untreated. The number of conditions being screened globally is expanding rapidly in parallel with advances in technology, diagnosis, and treatment availability for these conditions. In Hong Kong, NBS for inborn errors of metabolism (NBSIEM) began as a pilot program in October 2015 and was implemented to all birthing hospitals within the public healthcare system in phases, with completion in October 2020. The number of conditions screened for increased from 21 to 24 in April 2016 and then to 26 in October 2019. The overall recruitment rate of the NBS program was 99.5%. In the period between October 2015 and December 2022, 125,688 newborns were screened and 295 were referred back for abnormal results. The recall rate was reduced from 0.26% to 0.12% after the implementation of second-tier testing. An inherited metabolic disorder (IMD) was eventually confirmed in 47 infants, making the prevalence of IMD in Hong Kong 1 in 2674. At the time of the NBS result, 78.7% of the newborns with IMD were asymptomatic. There were two deaths reported: one newborn with methylmalonic acidemia cobalamin B type (MMACblB) died after the initial crisis and another case of carnitine palmitoyltransferase II deficiency (CPTII) died at 18 months of age after metabolic decompensation. The most common IMD noted were disorders of fatty acid oxidation metabolism (40%, 19 cases), closely followed by disorders of amino acid metabolism (38%, 18 cases), with carnitine uptake defect (19.1%, 9 cases) and citrullinemia type II (17%, 8 cases) being the two most common IMD picked up by the NBSIEM in Hong Kong. Out of the all the IMDs identified, 19.1% belonged to diverse ethnic groups. False negative cases were reported for citrullinemia type II and congenital adrenal hyperplasia during this period.

With the advancements in prenatal diagnostics, genome sequencing is now incorporated into clinical use to maximize the diagnostic yield following uninformative conventional tests (karyotype and chromosomal microarray analysis). Hong Kong started publicly funded prenatal genomic sequencing as a sequential test in the investigation of fetal structural anomalies in April 2021. The objective of the study was to evaluate the clinical performance and usefulness of this new service over one year. We established a web-based multidisciplinary team to facilitate case selection among the expert members. We retrospectively analyzed the fetal phenotypes, test results, turnaround time and clinical impact in the first 15 whole exome sequencing and 14 whole genome sequencing. Overall, the molecular diagnostic rate was 37.9% (11/29). De novo autosomal dominant disorders accounted for 72.7% (8/11), inherited autosomal recessive disorders for 18.2% (2/11), and inherited X-linked disorders for 9.1% (1/11). The median turnaround time for ongoing pregnancy was 19.5 days (range, 13–31 days). Our study showed an overall clinical impact of 55.2% (16/29), which influenced reproductive decision-making in four cases, guided perinatal management in two cases and helped future family planning in ten cases. In conclusion, our findings support the important role of genome sequencing services in the prenatal diagnosis of fetal structural anomalies in a population setting. It is important to adopt a multidisciplinary team approach to support the comprehensive genetic service.

We report two Hong Kong children with severe generalized epidermolysis bullosa simplex (EBS), the most severe form of EBS, without a family history of EBS. EBS is a rare genodermatosis usually inherited in an autosomal dominant fashion although rare autosomal recessive cases have been reported. Genetic studies in these patients showed that the first case was due to a novel de novo heterozygous variant, c.377T>G (NM_000526.5 (c.377T>G, p.Leu126Arg)) in the KRT14 gene and the second case was due to a rare de novo heterozygous variant c.527A>G (NM_000424.4, c.527A>G, p.Asn176Ser) in the KRT5 gene. To our knowledge, the c.377T>G variant in the KRT14 gene has not been previously reported, and the c.527A>G variant in the KRT5 gene is a rare cause of severe generalized EBS. In severe generalized EBS, infants exhibit severe symptoms at the onset; however, they tend to improve with time. A precise genetic diagnosis in these two cases aided in counseling the families concerning the prognosis in their affected children and the recurrence risk for future pregnancies.