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.

Who should return for an oral glucose tolerance test? A proposed clinical pathway based on retrospective analysis of 332 children

OBJECTIVES

Fasting plasma glucose or oral glucose tolerance test (OGTT) is the traditional diagnostic tool for type 2 diabetes (T2DM). However, fasting is required and implementation in all overweight/obese subjects is not practical. This study aimed to formulate a clinical pathway to stratify subjects according to their risk of abnormal OGTT.

METHODS

This retrospective study included patients with overweight or obesity who had undergone OGTT in a tertiary paediatric unit from 2012 to 2018. The optimal haemoglobin A1c (HbA1c) cutoff that predicts abnormal OGTT was evaluated. Other non-fasting parameters, in combination with this HbA1c cutoff, were also explored as predictors of abnormal OGTT.

RESULTS

Three hundred and thirty-two patients (boys: 54.2%, Chinese: 97.3%) were included for analysis, of which, 272 (81.9%) patients had normal OGTT while 60 (18.0%) patients had abnormal OGTT (prediabetes or T2DM). Optimal HbA1c predicting abnormal OGTT was 5.5% (AUC 0.71; sensitivity of 66.7% and specificity of 71%). When HbA1c≥5.5% was combined with positive family history and abnormal alanine transaminase (ALT) level, the positive predictive value for abnormal OGTT was increased from 33.6 to 61.6%.

CONCLUSIONS

HbA1c, family history of T2DM and ALT level could be used to derive a clinical pathway to stratify children who have high risk of abnormal OGTT.

Cost-benefit analysis of Hyperphenylalaninemia Due to 6-Pyruvoyl-Tetrahydropterin Synthase (PTPS) Deficiency: For Consideration of Expanded Newborn Screening in Hong Kong

Objectives

To evaluate the cost-benefit of implementing an expanded newborn screening programme for hyperphenylalaninemias due to 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency in Hong Kong.

Setting

Regional public hospitals in Hong Kong providing care for cases of inborn errors of metabolism.

Methods

Implementational and operational costs of a new expanded mass spectrometry-based newborn screening programme were estimated. Data on various medical expenditures for the mild and severe phenotypic subtypes were gathered from a case cohort diagnosed with PTPS deficiency from 2001 to 2009. Local incidence from a previously published study was used.

Results

Implementation and operational costs of an expanded newborn screening programme in Hong Kong were estimated at HKD 10,473,848 (USD 1,342,801) annually. Assuming a birthrate of 50,000 per year and an incidence of 1 in 29,542 live births, the medical costs and adjusted loss of workforce per year would be HKD 20,773,207 (USD 2,663,232). Overall the annual savings from implementing the programme would be HKD 9,632,750 (USD 1,234,968).

Conclusions

Our estimates show that implementation of an expanded newborn screening programme in Hong Kong is cost-effective, with a significant annual saving for public expenditure.