Whole exome sequencing reveals two novel compound heterozygous mutations in TWNK as a cause of the hepatocerebral form of mitochondrial DNA depletion syndrome: a case report

Abstract

Background Although Mitochondrial DNA depletion syndrome (MDS) can be classified into three forms: myopathic, encephalomyopathic and hepatocerebral form, it is difficult to identify its form due to its clinical heterogeneity. Therefore, it is very important to conduct molecular genetic analysis on suspected patients. This study presented a male 38 weeks and 5 days infant with liver cytolysis and leukodystrophy. Case presentation A male infant proband was admitted to the department of NICU for feeding intolerance, irregular rhythm of respiration, hypoglycemia, lactic acidosis, liver cytolysis and neurological abnormalities. He was onset of mild jaundice with leukodystrophy and high lactate and phenylderivatives for urine organic acids on the 7th day. Whole exome sequencing (WES) and Sanger sequencing were performed to screen and confirm the suspicious pathogenic mutations. The results revealed this proband carried two compound heterozygous mutations in TWNK : c.1186 C > T / p.Pro396Ser and c.1844 G > C / p.Gly615Ala inherited by an autosomal recessive form from his parents, of which protein conservative analysis and structural modeling supported the pathogenicity of the two mutations. Unfortunately, the conditions described above were not improved until he was discharged from the hospital on the 23rd day and died at 4 months of age. Conclusions In this study, we investigated a Chinese family with the hepatocerebral form of MDS and conducted WES and Sanger sequencing to explore the causative mutations for this proband born from non-consanguineous and healthy parents. We identified two novel TWNK c.1186 C > T/ c.1844 G > C compound heterozygous mutations which were probably the disease-causing mutations of hepatocerebral form of MDS and described the clinical manifestations of the proband, which expanded the phenotypic spectrum of MDS caused by variants in TWNK . This study also emphasized WES technology can provide the genetic diagnosis of Mendelian genetic disease.

Next‐generation sequencing identifies rare pathogenic and novel candidate variants in a cohort of Chinese patients with syndromic or nonsyndromic hearing loss

“…Perrault syndrome 5 (PRLTS) is an autosomal recessive disorder characterized by sensorineural HL, female hypogonadotropic hypogonadism, and neurologic symptoms including ataxia, sensory neuropathy, nystagmus, muscle weakness, ophthalmoplegia, and intellectual disability (Li et al, 2019; Morino et al, 2014). In family HL21, we identified a biallelic mutation of c.1172G>A (p.R391H)/c.1844G>C (p.G615A) in TWNK in proband HL21‐Ⅱ1 and her affected younger brother HL21‐Ⅱ2.…”

“…In family HL21, we identified a biallelic mutation of c.1172G>A (p.R391H)/c.1844G>C (p.G615A) in TWNK in proband HL21-Ⅱ1 and her affected younger brother HL21-Ⅱ2. Both c.1172G>A (Morino et al, 2014) and c.1844G>C (Li et al, 2019) are known pathogenic mutations, and were inherited from the proband's father and mother, respectively. The two patients, aged 8 and 6 years at the time of evaluation, shared identical symptoms of progressive sensorineural HL from moderate to profound with onset at around 4 years of age.…”

Genetic aetiologies of acute liver failure

“…MtDNA replication is also maintained by TWNK encoding a helicase required for unwinding mtDNA. In its severe form, mtDNA depletion syndrome ensues with ALF and neurological abnormalities at birth 76,77 …”

Mitochondrial DNA Depletion Syndrome and Its Associated Cardiac Disease

“…Mutations in this gene are associated with mitochondrial DNA depletion syndrome 7 (MTDPS7). Li et al found that the proband carried two TWNK compound heterozygous mutations, of which c.1186C>T (p.Pro396Ser) in exon 1 was inherited from the father, and c.1844G>C (p.Gly615Ala) in exon 5 was inherited from the mother ( 130 ). Dominant mutations in TWNK cause progressive ophthalmoplegia, mtDNA deletion, and autosomal dominant inheritance 3, while recessive mutations often lead to MTDPS 7 and Perrault syndrome 5.…”