STAC3 disorder: a common cause of congenital hypotonia in Southern African patients

STAC3 disorder, or Native American myopathy, is characterised by congenital myopathy, hypotonia, musculoskeletal and palatal anomalies, and susceptibility to malignant hyperthermia. A STAC3 c.851 G > C (p.Trp284Ser) pathogenic variant, common in the Lumbee Native American tribe, has been identified in other populations worldwide, including patients of African ancestry. We report on the frequency of STAC3 c.851 G > C in a cohort of 127 patients presenting with congenital hypotonia that tested negative for spinal muscular atrophy and/or Prader-Willi syndrome. We present a clinical retrospective, descriptive review on 31 Southern African patients homozygous for STAC3 c.851 G > C. The frequencies of various phenotypic characteristics were calculated. In total, 25/127 (20%) laboratory-based samples were homozygous for STAC3 c.851 G > C. A carrier rate of 1/56 and a predicted birth rate of 1/12 500 was estimated from a healthy cohort. A common haplotype spanning STAC3 was identified in four patients. Of the clinical group, 93% had a palatal abnormality, 52% a spinal anomaly, 59% had talipes equinovarus deformity/deformities, 38% had arthrogryposis multiplex congenita, and 22% had a history suggestive of malignant hyperthermia. The novel finding that STAC3 disorder is a common African myopathy has important clinical implications for the diagnosis, treatment and genetic counselling of individuals, with neonatal and/or childhood hypotonia with or without arthrogryposis multiplex congenita, and their families. The spread of this variant worldwide and the allele frequency higher in the African/African-American ancestry than the Admixed Americans, strongly indicates that the STAC3 c.851 G > C variant has an African origin which may be due to an ancient mutation with migration and population bottlenecks.

The First Case of Huntington's Disease like 2 in Mali, West Africa

Background

Huntington's disease like 2 (HDL2) has been reported exclusively in patients with African ancestry, mostly originating from South Africa.

Case report

We report three patients in Mali including a proband and his two children who have been examined by neurologists and psychiatrists after giving consent. They were aged between 28 and 56 years old. Psychiatric symptoms were predominant in the two younger patients while the father presented mainly with motor symptoms. Genetic testing identified a heterozygous 40 CTG repeat expansion in the Junctophilin-3 (JPH3) gene in all three patients.

Discussion

This study supports the hypothesis that HDL2 may be widely spread across Africa.

Highlights

We report here the first case of HDL2 in West Africa, suggesting that HDL2 is widely spread across African continent, and increasing access to genetic testing could uncover other cases.

The implementation and utility of clinical exome sequencing in a South African infant cohort

Genetic disorders are significant contributors to infant hospitalization and mortality globally. The early diagnosis of these conditions in infants remains a considerable challenge. Clinical exome sequencing (CES) has shown to be a successful tool for the early diagnosis of genetic conditions, however, its utility in African infant populations has not been investigated. The impact of the under-representation of African genomic data, the cost of testing, and genomic workforce shortages, need to be investigated and evidence-based implementation strategies accounting for locally available genetics expertise and diagnostic infrastructure need to be developed. We evaluated the diagnostic utility of singleton CES in a cohort of 32 ill, South African infants from two State hospitals in Johannesburg, South Africa. We analysed the data using a series of filtering approaches, including a curated virtual gene panel consisting of genes implicated in neonatal-and early childhood-onset conditions and genes with known founder and common variants in African populations. We reported a diagnostic yield of 22% and identified seven pathogenic variants in the NPHS1, COL2A1, OCRL, SHOC2, TPRV4, MTM1 and STAC3 genes. This study demonstrates the utility value of CES in the South African State healthcare setting, providing a diagnosis to patients who would otherwise not receive one and allowing for directed management. We anticipate an increase in the diagnostic yield of our workflow with further refinement of the study inclusion criteria. This study highlights important considerations for the implementation of genomic medicine in under-resourced settings and in under-represented African populations where variant interpretation remains a challenge.

Identifying the genetic causes of developmental disorders and intellectual disability in Africa: a systematic literature review

Objective: Genetic variants cause a significant portion of developmental disorders and intellectual disabilities (DD/ID), but clinical and genetic heterogeneity makes identification challenging. Compounding the issue is a lack of ethnic diversity in studies into the genetic aetiology of DD/ID, with a dearth of data from Africa. This systematic review aimed to comprehensively describe the current knowledge from the African continent on this topic. Method: Applicable literature published up until July 2021 was retrieved from PubMed, Scopus and Web of Science databases, following PRISMA guidelines, focusing on original research reports on DD/ID where African patients were the focus of the study. The quality of the dataset was assessed using appraisal tools from the Joanna Briggs Institute, whereafter metadata was extracted for analysis. Results: A total of 3,803 publications were extracted and screened. After duplicate removal, title, abstract and full paper screening, 287 publications were deemed appropriate for inclusion. Of the papers analysed, a large disparity was seen between work emanating from North Africa compared to sub-Saharan Africa, with North Africa dominating the publications. Representation of African scientists on publications was poorly balanced, with most research being led by international researchers. There are very few systematic cohort studies, particularly using newer technologies, such as chromosomal microarray and next-generation sequencing. Most of the reports on new technology data were generated outside Africa. Conclusion: This review highlights how the molecular epidemiology of DD/ID in Africa is hampered by significant knowledge gaps. Efforts are needed to produce systematically obtained high quality data that can be used to inform appropriate strategies to implement genomic medicine for DD/ID on the African continent, and to successfully bridge healthcare inequalities.

Molecular genetic characterization of Congolese patients with oculocutaneous albinism

BACKGROUND

Oculocutaneous albinism (OCA) is an autosomal recessive genetic disorder associated with reduced or absent pigmentation in the skin, hair and eyes. OCA type 2 (OCA2) is the most common type in Sub-Saharan Africa, related to a recurrent 2.7 kb intragenic deletion. Genomic data from Congolese patients are lacking. We aimed to describe genetic causes of OCA2 in a cohort of Congolese persons with OCA, and explore possible genotype-phenotype correlations.

METHODS

A cross sectional study was conducted from January 2015 to December 2017 in Kinshasa, Democratic Republic of Congo (DRC). 165 Congolese unrelated families with non-syndromic OCA, identified through patients' associations, consented to participate to this study. All index cases were tested for the known 2.7 kb deletion involving the exon 7 of the OCA2 gene. Patients heterozygous for the deletion underwent Sanger sequencing of all exons and flanking sequences in the OCA2 gene. Family segregation was performed for candidate pathogenic variants.

RESULTS

The 2.7 kb deletion in the OCA2 gene was identified in 136/165 (82.4%) index cases, including 113 (68.5%) homozygotes and 23 (13.9%) heterozygotes. Sanger sequencing identified a pathogenic or likely pathogenic variant in the OCA2 gene in 12 out of 23 heterozygotes investigated (52.1%). Segregation analysis allowed us to locate the point mutation on the trans allele in the three patients from whom parental DNA was available.

CONCLUSION

The OCA2 2.7 kb deletion is the major cause of non-syndromic OCA in Congolese patients recruited in this study, confirming results from other Sub-Saharan African populations. Several additional mutations were detected in OCA patient's heterozygote for the deletion, with to date no evidence for a second frequent founder mutation. The confirmation of a single mutation as the major cause will facilitate genetic counselling in this country.

Intergenerational Influence of Gender and the DM1 Phenotype of the Transmitting Parent in Korean Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common autosomal-dominant disorder caused by the CTG repeat expansion of the DMPK, and it has been categorized into three phenotypes: mild, classic, and congenital DM1. Here, we reviewed the intergenerational influence of gender and phenotype of the transmitting parent on the occurrence of Korean DM1. A total of 44 parent–child pairs matched for the gender of the transmitting parent and the affected child and 29 parent–child pairs matched for the gender and DM1 phenotype of the transmitting parent were reviewed. The CTG repeat size of the DMPK in the affected child was found to be significantly greater when transmitted by a female parent to a female child (DM1-FF) (median, 1309 repeats; range, 400–2083) than when transmitted by a male parent to a male child (650; 160–1030; p = 0.038 and 0.048 using the Tukey HSD and the Bonferroni test) or by a male parent to a female child (480; 94–1140; p = 0.003). The difference in the CTG repeat size of the DMPK between the transmitting parent and the affected child was also lower when transmitted from a male parent with classic DM1 (−235; −280 to 0) compared to when it was transmitted from a female parent with mild DM1 (866; 612–905; p = 0.015 and 0.019) or from a female parent with classic DM1 (DM1-FC) (605; 10–1393; p = 0.005). This study highlights that gender and the DM1 phenotype of the transmitting parent had an impact on the CTG repeat size of the DMPK in the affected child, with greater increases being inherited from the DM1-FF or DM1-FC situations in Korean DM1.

Global prevalence of myotonic dystrophy: an updated systematic review and meta-analysis

INTRODUCTION

Myotonic dystrophy (DM), the most common muscular dystrophy in adults, is a group of autosomal inherited neuromuscular disorders characterized by progressive muscle weakness, myotonia and cardiac conduction abnormalities. Due to the different gene mutations, DM has been subclassified into myotonic dystrophy type 1 (DM1) and type 2 (DM2). However, the prevalence studies on DM and its subtypes are insufficient.

METHODS

The PubMed (1966-2022), MEDLINE (1950-2022), Web of Science (1864-2022) and Cochrane Library (2022) databases were searched for original research articles published in English. The quality of the included studies was assessed by a checklist adapted from STrengthening the Reporting of OBservational studies in Epidemiology (STROBE). To derive the pooled epidemiological prevalence estimates, a meta-analysis was performed using the random effects model. Heterogeneity was assessed using the Cochrane Q statistic and the I2 statistic.

RESULTS

A total of 17 studies were included in the systematic review and meta-analysis. Of the 17 studies evaluated, 14 studies were considered medium quality, two studies were considered high quality and one study was considered low quality. The global prevalence of DM varied widely from 0.37 to 36.29 cases per 100,000. The pooled estimate of the prevalence of DM was 9.99 cases (95% CI: 5.62-15.53) per 100,000. The pooled estimate of the prevalence of DM1 was 9.27 cases (95% CI: 4.73-15.21) per 100,000, ranging from 0.37-36.29 cases per 100,000. The pooled estimate of the prevalence of DM2 was 2.29 cases (95% CI: 0.17-6.53) per 100,000, ranging from 0.00-24.00 cases per 100,000.

CONCLUSION

Our study provided accurate estimates of the prevalence of myotonic dystrophy. The high heterogeneity and the lack of high-quality studies highlight the need to conduct higher quality studies on orphan diseases.

Has translational genomics come of age in Africa?

The rapid increase in genomics research in Africa and the growing promise of precision public health begs the question of whether African genomics has come of age and is being translated into improved healthcare for Africans. An assessment of the continent's readiness suggests that genetic service delivery remains limited and extremely fragile. The paucity of data on mutation profiles for monogenic disorders and lack of large genome-wide association cohorts for complex traits in African populations is a significant barrier, coupled with extreme genetic variation across different regions and ethnic groups. Data from many different populations is essential to developing appropriate genetic services. Of the proposed genetic service delivery models currently used in Africa-Uncharacterized, Limited, Disease-focused, Emerging and Established-the first three best describe the situation in most African countries. Implementation is fraught with difficulties related to the scarcity of an appropriately skilled medical genetic workforce, limited infrastructure and processes, insufficient health funding and lack of political support, and overstretched health systems. There is a strong nucleus of determined and optimistic clinicians and scientists with a clear vision, and there is hope for innovative solutions and technological leapfrogging. However, a multi-dimensional approach with active interventions to stimulate genomic research, clinical genetics and overarching healthcare systems is needed to reduce genetic service inequalities and accelerate precision public health on the continent. Human and infrastructure capacity development, dedicated funding, political will and supporting legislation, and public education and awareness, are critical elements for success. Africa-relevant genomic and related health economics research remains imperative with an overarching need to translate knowledge into improved healthcare. Given the limited data and genetic services across most of Africa, the continent has not yet come of 'genomics' age.

African genetic diversity and adaptation inform a precision medicine agenda

The deep evolutionary history of African populations, since the emergence of modern humans more than 300,000 years ago, has resulted in high genetic diversity and considerable population structure. Selected genetic variants have increased in frequency due to environmental adaptation, but recent exposures to novel pathogens and changes in lifestyle render some of them with properties leading to present health liabilities. The unique discoverability potential from African genomic studies promises invaluable contributions to understanding the genomic and molecular basis of health and disease. Globally, African populations are understudied, and precision medicine approaches are largely based on data from European and Asian-ancestry populations, which limits the transferability of findings to the continent of Africa. Africa needs innovative precision medicine solutions based on African data that use knowledge and implementation strategies aligned to its climatic, cultural, economic and genomic diversity.

Pregestational screening of hereditary deafness genes carriers in 10,684 normal pregnant women in Zhuzhou, China

BACKGROUND

Mutations in genes associated with deafness differ between ethnic groups and regions in China. In this study, we investigated the genes associated with deafness in pregnant women to analyze the distribution of mutations leading to deafness in Zhuzhou, China.

METHODS

A total of 10,684 pregnant women were enrolled in this study. DNA samples were collected to detect the 14 common mutations in deafness genes (at 108 sites).

RESULTS

Prevalence of mutations in deafness genes in pregnant women with normal hearing in Zhuzhou was 4.92% (526/10,684). Among these 526 pregnant women with deafness gene mutations, the frequencies of mutated GJB2, GJB3, SLC26A4, and mtDNA 12S rRNA were 40.11, 7.22, 40.68, and 11.98%, respectively. The hotspots for mutations in the deafness genes were: c.235delC in GJB2 (31.18%), c.919-2A > G in SLC26A4 (18.44%), c.299_300delAT in GJB2 (5.70%), m.7444G > A in mtDNA 12S rRNA (5.70%), c.1229C > T in SLC26A4 (5.51%), m.1555A > G in mtDNA 12S rRNA (5.32%), accounting for 71.85%. Moreover, husbands of the 526 pregnant women who carried the deafness gene mutations were also included in the analysis to detect deafness gene mutations. Among the 526 husbands, 23 husbands carried mutations in deafness genes, accounting for 4.37%. The deafness gene mutations of the husbands and pregnant wives were not the same. In addition, the results of the neonatal follow-up hearing tests were all normal.

CONCLUSION

Our study identified the prevalence of mutations in GJB2, SLC26A4, mtDNA 12S rRNA, and GJB3 genes in pregnant women from Zhuzhou, China.