Zhou Yan and Jie Shenghua, Department of Infection, Wuhan Union Medical College Hospital Jie Shenghua There is a wide range of genetic metabolic diseases, more than one thousand of which have been identified, most of which are autosomal recessive. Among them, genetic metabolic liver diseases account for a high proportion, with jaundice, hepatomegaly, increased liver enzymes and hypoglycemia as the main features, including disorders of bilirubin metabolism, lipid metabolism, carbohydrate metabolism, abnormal amino acid and protein and enzyme metabolism, as well as metal element metabolism. Advances in molecular biology diagnostic techniques have promoted research in the diagnosis and treatment of genetic metabolic diseases, and assays such as polymerase chain reaction technique (PCR), denaturing gradient gel electrophoresis (DGGE), single-strand conformational polymorphism analysis (SSCP), denaturing high performance liquid chromatography (DHPLC), and gene clone sequencing have gradually become routine methods for the diagnosis of molecular genetic diseases, resulting in the diagnosis rate of inborn metabolic defects The diagnostic rate of inborn metabolic disorders has increased significantly. Somatic hyperbilirubinemia (also known as somatic jaundice) is an abnormality of bilirubin metabolism caused by autosomal dominant or recessive genetic variants that result in defects in the metabolism of certain enzymes, mostly congenital hyperbilirubinemia. Among them, Gilbert syndrome, Crigler-Najjar syndrome and Lucey-driscoll syndrome are characterized by unconjugated bilirubin increase; Dubin-johnson syndrome and Rotor syndrome are characterized by conjugated bilirubin increase. Gilbert syndrome (GS) Gilbert syndrome was first reported by Gilbert and Lereboullet in 1901 and presents as a nonhemolytic, intermittent nonconjugated hyperbilirubinemia without organic lesions in the liver. The increase in unconjugated bilirubin levels is often within 5 times the upper limit of normal, which is an important indicator to distinguish it from Crigler-Najjar syndrome. The disease can be exacerbated or triggered by starvation, surgery, fever, infection, exertion, alcohol consumption, or the combination of other diseases. It is more common to develop at the age of 18-30, with a male to female ratio of about 4:1 and an incidence of about 2% to 6%. GS is caused by a defect in the uridine diphosphate glucuronosyltransferase 1A1 gene (UGT1A1) at the chromosome 2q37 locus that significantly reduces the expression level or activity of glucuronosyltransferase (UGT), and this gene polymorphism is the molecular genetic basis of GS. Three forms of UGT1A1 gene expression defects have been identified: ① Single base mutation (missense mutation) type in the coding region. It is located in 5 pairs of exon regions, including G71R, G493R, P364L, P229Q, F83L, R367G and Y486D, with the most frequent G→A point mutation (G71R) at nucleotide 211, commonly found in Asians. ② promoter TATA box TA insertion type. It manifests as a dinucleotide (TA) insertion into the TATA box about 25-35 bp upstream of the UGT1A1 gene promoter, causing the normal wild-type A(TA)6TAA mutation to A(TA)7TAA, with some patients showing polymorphisms such as (TA)5 or (TA)8, common in western whites. (iii) gtPBREM T-3279G mutant. gtPBREM is located approximately 3 kb upstream of TATA in the region -3483/-3194. Shen Jian et al. reported the first patient in China with a T-3279G mutation in the gtPBREM region combined with A(TA)7TAA, and this mutation was significantly associated with increased bilirubin levels due to decreased transcriptional activity of the gene. In addition, a high degree of linkage disequilibrium was found between the UGT1A1 gene-3279 locus and the TATA cassette, and the combination of the two reduced UGT1A1 transcriptional activity to 30% or less. The diagnosis of GS can be made by immunohistochemical examination of liver tissue with UGT1A polyclonal antibodies to determine the degree of intrahepatic UGT activity or by molecular biology techniques. genetic polymorphism of the TATAA sequence in the promoter region of the associated UGT1A gene. Crigler-Najjar Syndrome (CNS) Crigler-Najjar syndrome is a rare congenital glucuronosyltransferase deficiency resulting in hereditary hyperbilirubinemia that occurs in newborns and infants. It is classified into type I and type II, depending on the degree of UGT deficiency. Type I CNS is rare, first reported by Crigler-Najjar in 1952, and is a pure heterozygote for the CNS-causing gene, autosomal recessive, and the parents are mostly consanguineous. Type II CNS is rare, but more common than type I. It is a heterozygote for the CNS-causing gene and was discovered by Arias in 1962, so it is also called Arias syndrome. It is generally believed that type II CNS is inherited in an autosomal dominant manner with incomplete epimutation, and parents are rarely inbred. CNS is caused by mutations in the coding region of the UGT1A1 gene, in which there is a complete (type I) or partial loss of UGT activity (type II), which directs the synthesis of the gene. Mutations can occur in any of the five exons of the UGT1A1 gene and can cause premature translation termination or code-shifting mutations, resulting in amino acid sequence changes or deletions and loss of enzyme activity. More than seventy UGT1A1 exon mutations have been reported. The mutations related to type I CNS include C1070G, T877A, G377V, Q357R, S375F, G308E, A291V, H39D and Q239fsX256. Nearly twenty UGT1A1 gene mutation loci have been found to be associated with type II CNS at home and abroad, including Y486D, P229G, Q331R, V225G, P387S, G395V, W354R, R336Q, R336L, R336W, N279Y and W461R. Different UGT1A1 gene mutation loci exist in different ethnic and racial groups as well as different family lines of CNS. Recently, two new mutations were reported in a pregnant woman with type II CNS: IVS1+5 and C1175T. In addition to exon variants leading to loss of enzyme activity, mutations in introns and shear site genes can also lead to code shift mutations, causing loss of enzyme activity. Liver biopsy for residual bilirubin glucuronide activity or bile composition analysis is reliable for the diagnosis of CNS, but both are invasive tests, and genetic tests are now becoming popular. Lucey-Driscoll syndrome (L-D syndrome) L-D syndrome, also known as transient familial neonatal hyperbilirubinemia, is a rare form of congenital nonhemolytic jaundice in which the infant develops jaundice within 48 h of birth, with unconjugated bilirubin in the blood reaching 340 μmol/L or more. The pathogenesis is thought to be related to the presence of a glucuronosyltransferase inhibitor in the plasma of the mother during the last trimester of pregnancy, possibly a progesterone steroid (progestogen), causing impaired uptake and conjugation of bilirubin by hepatocytes, the exact pathogenesis of which is not fully understood. The disease is aggressive and some children can die from kernicterus within a short period of time. However, the jaundice is only temporary and serum bilirubin often returns to normal within 1 month after transfusion and blood exchange therapy and phototherapy. Like Gilbert syndrome and Crigler-Najjar syndrome, L-D syndrome is caused by a defect in the UGT1A1 gene. Dubin-Johnson syndrome (DJS) DJS, also known as chronic idiopathic jaundice, is a mild chronic intermittent hyperbilirubinemia, first reported by Dubin et al. in 1954, and is autosomal recessive. The disease is characterized by chronic hyperconjugated bilirubinemia, impaired excretion of selectively bound anions, and dark brown liver due to pigmentation, and the patient is a pure heterozygote for the causative gene of Dubin-Johnson syndrome. The disease appears to be more frequent in males and can affect more than one family. Although the disease is present from birth, it is often discovered incidentally in adolescence or is chronically misdiagnosed as other liver or gallbladder disease. It is now widely believed that the defective expression of MRP2/cMOAT is due to mutations in codon 1066 of the ABCC2 gene, which encodes multidrug resistance-associated protein (MRP)2 or multispecific organic anion transport protein (MRP2/cMOAT) at the hepatic capillary bile ducts, resulting in abnormal transport of organic anions, especially amphoteric compounds such as bilirubin diglucosylate, by the capillary bile ducts. Congenital impaired hepatocyte bilirubin excretion and defective excretion of non-water-soluble organic anions, but normal excretion of bile salts, are important for the development of DJS. MRP2 (encoding gene ABCC2), an important transporter of ATP-dependent organic anions, such as bilirubin diglucosylate, sulfate, and reduced glutathione, is an important factor in the formation of non-bile salt-dependent bile flow. The ABCC2 gene is located on chromosome 10q24 and is 45 kb, including 32 exons, and different types of MRP2/ABCC2 gene mutations exist in different races. Most are single mutations, including nonsense mutations (C974G, Y1275X), gene deletions (2748del136, 3615del229, del3399-3400) or missense mutations (L1441M, E1352Q, C2302T, T2125C), but multiple mutations at the cDNA level (e.g. nonsense codon and exon skipping), and C-24T and C3972T were pure mutants of ABCC2 gene, while there was also a gene deletion of 1008BP (segment IVS6-275 to IVS7+498) at exon 7 of ABCC2 gene. The detection of the ABCC gene, especially the gene encoding the MRP2 segment, is useful for the diagnosis of DJS, as well as for the diagnosis of transport disorders of exogenous amphoteric anions such as sodium sulfobromopeptide and indocyanine green. In addition, laparoscopy reveals a dark brown appearance of the liver. The sensitivity of laparoscopic diagnosis of DJS was reported by Guo Changji et al. to be 100%, which is an important method for diagnosing and identifying DJS. Rotor syndrome (RS) Rotor syndrome is a type II hereditary increased conjugated bilirubin, which was first reported by Rotor in 1948 and was initially thought to be a subtype of DJS, but organic anion clearance test and urinary fecal porphyrin isomer analysis confirmed that it is an independent disease and less common than DJS. There are very few studies on the mechanism of RS, but it is only known that RS is caused by congenital defects in the uptake of unconjugated bilirubin and excretion of conjugated bilirubin by hepatocytes, with a predominant increase in conjugated bilirubin in blood and a decrease in indocyanine green (ICG) excretion test, and is autosomal recessive. It has been reported that patients with RS have reduced levels of hepatic glutathione S-transferase, and it has been hypothesized that mutations in the HGSTA1-1 gene may be associated with its development. The disease is rare, benign lesions, almost always seen in persons under 20 years of age, independent of sex, and jaundice is often aggravated by alcohol consumption, infection, and surgery. The diagnosis can be confirmed by liver biopsy and 99mTc-HIDA biliary tract imaging, and the prognosis is good. Progressive Familial Intrahepatic Cholestasis (PFIC) PFIC is another severe cholestatic liver disease in infants and children, which is autosomal recessive and is mainly caused by mutations in specific hepatocyte transporter genes, resulting in the production, modification, and regulation of various functional proteins in the membranes of hepatocytes and bile duct epithelial cells. It is mainly caused by mutations in specific hepatocyte transporter genes, resulting in defects in the production, modification and regulation of various functional proteins in the membranes of hepatocytes and bile duct epithelial cells, leading to hepatocellular cholestasis. Incomplete mutations in inherited transporter genes can increase the susceptibility of individuals to acquired liver injury leading to cholestasis. The disease has been found to be classified into 4 types: ① PFIC-1 type (Byler’s disease). It is associated with a mutation in the ATP8B1 gene on chromosome 18q21-22 causing a familial intrahepatic cholestasis-associated protein-1 (FIC1) defect. Mutation analysis showed that most of the ATP8B1 gene mutations are nonsense mutations and deletion mutations, which severely affect the function of FIC1 protein. ②PFlC-2 type. Mutations in the ABCB11 gene on chromosome 2q24 affect the expression of capillary bile salt transport protein (BSEP) in the capillary bile duct membrane, leading to decreased bile salt secretion and thus allowing severe damage due to bile salt accumulation in hepatocytes. Most children with BSEP mutations, regardless of the type of mutation, do not express BSEP protein in the capillary bile duct membrane of hepatocytes. Severe phenotypes are often associated with mutations in protein truncation or protein production failure genes. Missense mutations can also affect protein assembly and transport or interfere with the structure of the functional region of the protein, leading to defects in bile acid secretion, so that detecting BSEP expression does not exclude functional defects in BSEP. The mechanism may be related to bile acid salt mutagenesis. (iii) PFIC-3 type. Mutations in the MDR3/ABCB4 gene on chromosome 7q21 affect the capillary bile duct phospholipid transporter, resulting in impaired phospholipid export. More than thirty ABCB4 mutations associated with PFIC-3 have been reported, with most cases having mutations located on both alleles. In nearly one-third of cases, the mutations result in truncated protein production, and the MDR3 glycoprotein is undetectable by liver immunostaining. This is due to the rapid degradation of the truncated protein after synthesis, resulting in very low protein levels, or the creation of a stop codon resulting in mRNA instability and decay of ABCB4. The other 2/3 cases are missense mutations, mostly in the highly conserved Walker A and B motifs involved in ATP binding, which do not affect the ATPase activity and transport process, but rather cause misassembly and functional defects in the intracellular MDR3 glycoprotein. cholesterol gallstone disease, followed by ICP, and finally biliary cirrhosis. (iv) PFIC-4 type. The pathogenesis is unknown, but is presumably related to an inherited defect in the bile acid synthesis pathway leading to impaired bile acid synthesis. The majority of patients are only effective with liver transplantation. Lipid metabolism disorders are qualitative and quantitative abnormalities of lipids and their metabolites in blood and other tissues and organs caused by congenital genetic factors. disease and Gaucher’s disease. Niemann-Pick Disease (NPD), also known as sphingomyelin deposition disease, is an autosomal recessive disorder. It is a systemic metabolic disease caused by a congenital deficiency of sphingomyelinase, which prevents the normal breakdown of sphingomyelin. It is inherited according to a simple Mendelian recessive pattern and is prevalent in young children, with a large number of neurosphingolipid-containing foam cells (Niemann-Pick cells) in mononuclear macrophages and the nervous system. The disease was first reported by Niemann in 1914 and was identified by Pick in 1922, hence the name, and is less common than Gaucher disease, with more Jewish cases. Six types of NK disease have been reported: infantile (A), visceral (B), subacute or juvenile (C), Nova-scotia (D), E, and F. Among them, types A and B are due to defective acid phospholipase activity, and their coding gene SMPD1 is localized at 11p15.1-15.4 and contains 6 exons, with regional and ethnic differences in mutation sites and mutation frequency in the SMPD1 gene, with mutation sites G21X, C92W, C157R, R376H and R376, H421Y, H422Y. types C and D Types C and D are due to defective intracellular cholesterol transport and are associated with NPC1 or NPC2 genes. Types E and F are not associated with mutations in the acid phospholipase gene. The diagnosis of the disease still relies on serum nerve sphingomyelin activity, urinary nerve sphingomyelin excretion, bone marrow examination, liver, spleen or lymph node biopsies and genetic analysis of tissue biopsies as more accurate methods. Gaucher Disease (GD) Gaucher disease is the most common form of lysosomal glycolipid storage disease and is inherited in an autosomal recessive manner. It was first reported by Gaucher in 1882 and is caused by a defective acidic β-glucosidase, also known as glucocerebrosidase (GC), in the lysosomes, which causes the accumulation of glucocerebrosides in the mononuclear macrophage system of various organs to form Gaucher cells, resulting in the loss of the original function of the cells. Current DNA technology can diagnose the allele encoding glucocerebrosidase at position 1q21 of the human chromosome, and there is a highly homologous pseudogene 16 kb downstream of this gene. Recently, foreign scholars have identified 42 mutations in the genotype of GD, including missense mutations, splice mutations, code shift mutations, deletions, gene and pseudogene fusion and gene conversion, etc. The five common mutation loci are N370S, L444P, R463C, 84GG, IVS2+1G-A. The most common of these mutations are missense mutations leading to a reduction in the catalytic function and stability of the synthesized GC. The most common of these are missense mutations leading to reduced GC catalytic function and stability of synthesis. The most common mutations in Asian patients are V15L, G46E, and N188S. Other mutated loci include F37V, R48Q, S196P, Y205C, R353W, V375L, W179X, and S271N. Some genotypes have been found to correlate with the phenotypes, for example, the N370S allele is mostly associated with type I GD patients; the L444P allele is mostly associated with the neurotypical phenotype, and L444P pure congeners tend to exhibit type III, while L444P usually exhibits type II when combined with other genes. DNA analysis is more reliable than enzymatic diagnosis, but there are many different mutations in this disease and some are still unidentified, so the disease cannot be completely excluded even if the analysis results are normal.