Allan-Herndon-Dudley syndrome in Hong Kong: Implication for newborn screening.

BACKGROUND: Allan-Herndon-Dudley syndrome (MCT 8 deficiency) is an X-linked recessive condition caused by hemizygous pathogenic variants in SLC16A2 encoding the monocarboxylate transporter 8 (MCT8). Patients present with global developmental delay and neurological impairment, and abnormal serum thyroid function tests. The drug, 3,3',5 triiodothyroacetic acid (TRIAC), was recently demonstrated to improve the endocrinological profile. Improvement in diagnostic approach is key to earlier start of treatment. PATIENT FINDINGS: We described four Chinese patients with MCT8 deficiency undergoing different diagnostic odysseys. Their initial presentation included global developmental delay and dystonia. Patient 2 also had epilepsy. Patients 1 and 2 presented with two novel variants: (1)hemizygous NM_006517.4(SLC16A2):c.1170 + 2 T > A; p.(?), and (2)hemizygous NM_006517.4(SLC16A2):c.305dupT; p.(Val103GlyfsTer17) respectively. Patients 3 and 4 were biological brothers harboring hemizygous NM_006517.4(SLC16A2):c.305dupT; p.(Val103GlyfsTer17), which was first reported in 2004. We obtained the measurement of triiodothyronine (T3) and reverse T3 (rT3) from dried blood spot samples collected on Day 1 of life from Patient 1 and studied the biomarkers (rT3 and T3/rT3 ratio) proposed by Iwayama et al. for the detection of MCT8 deficiency at birth. Our data verified the significantly reduced rT3 level in Patient 1, compared with healthy newborns, although low T3 level and comparable T3/rT3 ratio with controls were detected. SUMMARY: Patients with MCT8 deficiency often undergo diagnostic odysseys. An early diagnosis could be missed by a normal newborn thyroid function screening result based on biochemical measurement of TSH and/or T4/fT4. Early detection of rT3 is key to improving current diagnostic approach. CONCLUSION: We recommend that full thyroid function profile (TSH, T4/fT4, T3/fT3, rT3) be considered early for all pediatric patients presenting with unexplained developmental delay and/or dystonia. The potential inclusion of rT3 measurement in newborn screening may prove promising.

Mitochondrial diseases in Hong Kong: prevalence, clinical characteristics and genetic landscape.

OBJECTIVE: To determine the prevalence of mitochondrial diseases (MD) in Hong Kong (HK) and to evaluate the clinical characteristics and genetic landscape of MD patients in the region. METHODS: This study retrospectively reviewed the phenotypic and molecular characteristics of MD patients from participating public hospitals in HK between January 1985 to October 2020. Molecularly and/or enzymatically confirmed MD cases of any age were recruited via the Clinical Analysis and Reporting System (CDARS) using relevant keywords and/or International Classification of Disease (ICD) codes under the HK Hospital Authority or through the personal recollection of treating clinicians among the investigators. RESULTS: A total of 119 MD patients were recruited and analyzed in the study. The point prevalence of MD in HK was 1.02 in 100,000 people (95% confidence interval 0.81-1.28 in 100,000). 110 patients had molecularly proven MD and the other nine were diagnosed by OXPHOS enzymology analysis or mitochondrial DNA depletion analysis with unknown molecular basis. Pathogenic variants in the mitochondrial genome (72 patients) were more prevalent than those in the nuclear genome (38 patients) in our cohort. The most commonly involved organ system at disease onset was the neurological system, in which developmental delay, seizures or epilepsy, and stroke-like episodes were the most frequently reported presentations. The mortality rate in our cohort was 37%. CONCLUSION: This study is a territory-wide overview of the clinical and genetic characteristics of MD patients in a Chinese population, providing the first available prevalence rate of MD in Hong Kong. The findings of this study aim to facilitate future in-depth evaluation of MD and lay the foundation to establish a local MD registry.

Serum ceruloplasmin monitoring in a case of silver intoxication due to intravenous silver infusion.

INTRODUCTION: Colloidal silver packaged as a dietary supplement is readily available online and is thought to be safe. Literature describing its toxicity in humans is scarce. CASE REPORT: A 47-year-old man presented to us for sensory and gait problems. He had unremarkable past health except dystrophic nails. He further volunteered a history of receiving chronic oral and intravenous administration of colloidal silver. We confirmed his plasma silver was 1200-fold elevated, measuring 11990 nmol/L (normal < 10 nmol/L). He had deranged liver function tests, and liver biopsy showed distorted acinar architecture, bridging fibrosis and lymphocytic infiltrate with silver particles clustering along the vascular endothelium and portal venules. Brain magnetic resonance imagining showed features of mineralization over bilateral globus pallidi. There was biochemical evidence of central adrenal insufficiency, intracellular iron overload and hypoceruloplasminemia (<0.05 g/L). Gradual clinical and biochemical improvement was noted after silver cessation: his plasma silver dropped to 4800 nmol/L (3 months) and 1650 nmol/L (12 months), and serum ceruloplasmin reverted to 0.13 g/L (10 months) and 0.29 g/L (20 months). CONCLUSIONS: The potential effects of silver to liver and copper metabolism were shown in this case. Serum ceruloplasmin also serves as a surrogate marker in monitoring silver intoxication.

Urine organic acid as the first clue towards aromatic L-amino acid decarboxylase (AADC) deficiency in a high prevalence area.

BACKGROUND: Aromatic L-amino acid decarboxylase deficiency is a rare neurometabolic disease due to impaired decarboxylation of neurotransmitter precursors to its active form. CASE: We retrospectively reviewed 8 cases from 2008 to 2019 with cerebrospinal fluid neurotransmitter analysis performed at our centre. All cases had an elevated urine vanillactic acid and, in most cases, with N-acetylvanilalanine detected. Cerebrospinal fluid analysis showed low downstream metabolites vanillylmandelic acid, homovanillic acid but high 3-O-methyl-L-DOPA, 5-hydroxytryptophan. Cerebrospinal fluid pterins were normal. Genotyping in DDC confirms the diagnosis. Urine organic acid analysis provided the first clue to diagnosis in four of the cases, which then triggered cerebrospinal fluid neurotransmitter and genetic analysis. We also developed a diagnostic decision support system to assist the interpretation of the mass spectrometry data from urine organic acids. CONCLUSIONS: Urine organic acid could be essential in guiding subsequent investigations for the diagnosis of aromatic L-amino acid decarboxylase deficiency. We propose to screen suspected cases first with urine organic acids, specifically looking for vanillactic acid and N-acetylvanilalanine. Suggestive findings should be followed with target analysis for c.714 + 4A > T in ethnically Chinese patients. The assistive tool allowed expedite interpretation of profile data generated from urine organic acids analysis. It may also reduce interpreter's bias when peaks of interest are minor peaks in the spectrum.

Centrosome-associated CDC25B is a novel disease-causing gene for a syndrome with cataracts, dilated cardiomyopathy, and multiple endocrinopathies.

We describe a unique Chinese girl who presented with intrauterine growth retardation, delayed development, bilateral cataracts, hypothyroidism, growth hormone deficiency, and juvenile dilated cardiomyopathy. She was born to consanguineous parents with a history of one fetal and one infantile death in the family. She died from cardiac failure at the age of 12. In the pursuit of a diagnosis, the family was referred to the Clinics for Rare Diseases Referral and the University of Hong Kong Undiagnosed Disease Program. Whole-exome sequencing analysis revealed a homozygous non-sense variant, NM_021873:c.313G > T (p.Glu105*), in the CDC25B gene, a key regulator of the cell cycle. This variant was located in a region of homozygosity of 25 Mb on chromosome 20. Her parents and two asymptomatic sisters were confirmed to be carriers and one brother did not carry the variant. This is the first report of a natural human knockout of the CDC25B gene. Multiple endocrinopathies and fatal juvenile dilated cardiomyopathy suggests the potential for unfavorable complications in oncology patients receiving CDC25B inhibitors as an emerging targeted therapy.

Deoxythymidylate kinase, DTYMK, is a novel gene for mitochondrial DNA depletion syndrome.

BACKGROUND: Mitochondrial DNA depletion syndrome is a group of heterogeneous diseases with non-specific presentation. The common feature is the quantitative depletion of mitochondrial DNA without qualitative defects. Diagnosis of these diseases poses a challenge and whole exome sequencing is often needed for their diagnoses. CASE: Two siblings of a quartet family, presenting with hypotonia, microcephaly and severe intellectual disability, have been diagnosed to harbor two heterozygous variants in trans in the DTYMK gene of the thymidine biosynthesis pathway. Mitochondrial DNA depletion has been demonstrated in silico in the more severe sibling. CONCLUSIONS: We suggest the consideration of incorporating DTYMK as one of the associated genes of mitochondrial DNA depletion syndrome (MDDS). DTYMK may be the missing link in the mitochondrial nucleotide salvage pathway but further characterization and additional evidence would be needed.

Clinical whole-exome sequencing reveals a common pathogenic variant in patients with CoQ10 deficiency: An underdiagnosed cause of mitochondriopathy.

BACKGROUND: Primary CoQ deficiency occurs because of the defective biosynthesis of coenzyme Q, one of the key components of the mitochondrial electron transport chain. Patients with this disease present with a myriad of non-specific symptoms and signs, posing a diagnostic challenge. Whole-exome sequencing is vital in the diagnosis of these cases. CASE: Three unrelated cases presenting as either encephalopathy or cardiomyopathy have been diagnosed to harbor a common pathogenic variant c.370G > A in COQ4. COQ4 encodes a key structural component for stabilizing the multienzymatic CoQ biosynthesis complex. This variant is detected only among East and South Asian populations. CONCLUSIONS: Based on the population data and our case series, COQ4-related mitochondriopathy is likely an underrecognized condition. We recommend including the COQ4 c.370G > A variant as a part of the screening process for mitochondriopathy in Chinese populations.

Genetic diagnosis of CADASIL in three Hong Kong Chinese patients: A novel mutation within the intracellular domain of NOTCH3.

Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) is an adult onset hereditary stroke syndrome characterized by recurrent stroke and progressive cognitive impairment caused by NOTCH3 mutations. We report here the clinical and molecular findings of three unrelated Hong Kong Chinese families with CADASIL syndrome. Sanger sequencing of genomic DNA revealed a novel heterozygous variant NM_000435.2(NOTCH3):c.[5903_5904insATAA];[5903_5904=] NP_000426.2:p.(Asp1969∗);(Asp1969=) and two previously reported heterozygous mutations NM_000435.2(NOTCH3):c.[328C>T];[328C=] NP_000426.2:p.[(Arg110Cys)];[(Arg110=)] and NM_000435.2(NOTCH3):c.[580T>A];[580T=] NP_000426.2:p.(Cys194Ser);(Cys194=) in the three families respectively. Molecular basis of CADASIL in these three patients were further established. Genetic analysis provides a reliable method for confirming the diagnosis of CADASIL and enables proper genetic counseling and cascade testing.

A missense variant in SLC12A3 gene enhances aberrant splicing causing Gitelman syndrome.

Gitelman syndrome (GS) is the most prevalent genetic tubulopathy characterized by several electrolyte abnormalities, including hypokalemia, hypomagnesemia, hypocalciuria, metabolic alkalosis, and hyperreninemic hyperaldosteronism. These features are caused by a bi-allelic mutation in the SLC12A3 gene. In this report, we present a case of GS in an asymptomatic woman who incidentally exhibited hypokalemia during an antenatal check-up. Her biochemical profile was consistent with GS. Genetic analysis revealed two heterozygous variants in trans, namely, NM_001126108.2:c.625C>T; p.(Arg209Trp) and c.965C>T; p.(Ala322Val). The c.625C>T; p.(Arg209Trp) variant has previously been experimentally confirmed as a loss-of-function (LOF) variant. However, the functional impact of the c.965C>T variant, located at the 5 prime end of exon 8, has not been fully elucidated. Through the utilization of both complementary DNA (cDNA) and minigene analysis, we confirmed that the c.965C>T variant can generate two distinct cDNA transcripts. The first transcript carries a missense mutation, p.(Ala322Val) in the full SLC12A3 transcript, while the second transcript consists of an in-frame deletion of both exons 7 and 8 in the SLC12A3 transcript, in which may result in the loss of transmembrane regions 5 - 6 involved in chloride transport. Our findings provide insights into the intricate mechanisms of splicing, highlighting how a variant in one exon can remotely influence the transcription of an upstream exon, as observed with the variant in exon 8 impacting the transcription of exon 7.