Following dietary exposure to fructose, sucrose, or sorbitol, untreated hereditary fructose intolerance (HFI) is characterized by metabolic disturbances (hypoglycemia, lactic acidemia, hypophosphatemia, hyperuricemia, hypermagnesemia, hyperalaninemia) and clinical findings (nausea, vomiting, and abdominal distress; chronic growth restriction / failure to thrive). While untreated HFI typically first manifested when fructose- and sucrose-containing foods were introduced in the course of weaning young infants from breast milk, it is now presenting earlier, due to the addition of fructose-containing nutrients in infant formulas. If the infant ingests large quantities of fructose, the infant may acutely develop lethargy, seizures, and/or progressive coma. Untreated HFI may result in renal and hepatic failure. If identified and treated before permanent organ injury occurs, individuals with HFI can experience a normal quality of life and life expectancy.

Multiple acyl-CoA dehydrogenase deficiency (MADD) represents a clinical spectrum in which presentations can be divided into type I (neonatal onset with congenital anomalies), type II (neonatal onset without congenital anomalies), and type III (late onset). Individuals with type I or II MADD typically become symptomatic in the neonatal period with severe metabolic acidosis, which may be accompanied by profound hypoglycemia and hyperammonemia. Many affected individuals die in the newborn period despite metabolic treatment. In those who survive the neonatal period, recurrent metabolic decompensation resembling Reye syndrome and the development of hypertrophic cardiomyopathy can occur. Congenital anomalies may include dysmorphic facial features, large cystic kidneys, hypospadias and chordee in males, and neuronal migration defects (heterotopias) on brain MRI. Individuals with type III MADD, the most common presentation, can present from infancy to adulthood. The most common symptoms are muscle weakness, exercise intolerance, and/or muscle pain, although metabolic decompensation with episodes of rhabdomyolysis can also be seen. Rarely, individuals with late-onset MADD (type III) may develop severe sensory neuropathy in addition to proximal myopathy.

PMM2-CDG, the most common of a group of disorders of abnormal glycosylation of N-linked oligosaccharides, is divided into three clinical stages: infantile multisystem, late-infantile and childhood ataxia–intellectual disability, and adult stable disability. The clinical manifestations and course are highly variable, ranging from infants who die in the first year of life to mildly affected adults. Clinical findings tend to be similar in sibs. In the infantile multisystem presentation, infants show axial hypotonia, hyporeflexia, esotropia, and developmental delay. Feeding problems, vomiting, faltering growth, and developmental delay are frequently seen. Subcutaneous fat may be excessive over the buttocks and suprapubic region. Two distinct clinical courses are observed: (1) a nonfatal neurologic course with faltering growth, strabismus, developmental delay, cerebellar hypoplasia, and hepatopathy in infancy followed by neuropathy and retinitis pigmentosa in the first or second decade; and (2) a more severe neurologic-multivisceral course with approximately 20% mortality in the first year of life. The late-infantile and childhood ataxia–intellectual disability stage, which begins between ages three and ten years, is characterized by hypotonia, ataxia, severely delayed language and motor development, inability to walk, and IQ of 40 to 70; other findings include seizures, stroke-like episodes or transient unilateral loss of function, coagulopathy, retinitis pigmentosa, joint contractures, and skeletal deformities. In the adult stable disability stage, intellectual ability is stable; peripheral neuropathy is variable, progressive retinitis pigmentosa and myopia are seen, thoracic and spinal deformities with osteoporosis worsen, and premature aging is observed; females may lack secondary sexual development and males may exhibit decreased testicular volume. Hypogonadotropic hypogonadism and coagulopathy may occur. The risk for deep venous thrombosis is increased.

X-linked recessive nephrolithiasis with renal failure (XRN) is a form of X-linked hypercalciuric nephrolithiasis, which comprises a group of disorders characterized by proximal renal tubular reabsorptive failure, hypercalciuria, nephrolithiasis, and renal insufficiency. These disorders have also been referred to as the 'Dent disease complex' (Scheinman, 1998; Gambaro et al., 2004). For a general discussion of Dent disease, see 300009.

Low molecular weight proteinuria with hypercalciuria and nephrocalcinosis is a form of X-linked hypercalciuric nephrocalcinosis, a group of disorders characterized by proximal renal tubular reabsorptive failure, hypercalciuria, nephrocalcinosis, and renal insufficiency. These disorders have also been referred to as the 'Dent disease complex' (Scheinman, 1998; Gambaro et al., 2004). For a general discussion of Dent disease, see 300009.

Dent disease, an X-linked disorder of proximal renal tubular dysfunction, is characterized by low molecular weight (LMW) proteinuria, hypercalciuria, and at least one additional finding including nephrocalcinosis, nephrolithiasis, hematuria, hypophosphatemia, chronic kidney disease (CKD), and evidence of X-linked inheritance. Males younger than age ten years may manifest only LMW proteinuria and/or hypercalciuria, which are usually asymptomatic. Thirty to 80% of affected males develop end-stage renal disease (ESRD) between ages 30 and 50 years; in some instances ESRD does not develop until the sixth decade of life or later. The disease may also be accompanied by rickets or osteomalacia, growth restriction, and short stature. Disease severity can vary within the same family. Males with Dent disease 2 (caused by pathogenic variants in OCRL) may also have mild intellectual disability, cataracts, and/or elevated muscle enzymes. Due to random X-chromosome inactivation, some female carriers may manifest hypercalciuria and, rarely, renal calculi and moderate LMW proteinuria. Females rarely develop CKD.

X-linked recessive hypophosphatemic rickets is a form of X-linked hypercalciuric nephrolithiasis, which comprises a group of disorders characterized by proximal renal tubular reabsorptive failure, hypercalciuria, nephrocalcinosis, and renal insufficiency. These disorders have also been referred to as the 'Dent disease complex' (Scheinman, 1998; Gambaro et al., 2004). For a general discussion of Dent disease, see 300009.

Dent disease, an X-linked disorder of proximal renal tubular dysfunction, is characterized by low molecular weight (LMW) proteinuria, hypercalciuria, and at least one additional finding including nephrocalcinosis, nephrolithiasis, hematuria, hypophosphatemia, chronic kidney disease (CKD), and evidence of X-linked inheritance. Males younger than age ten years may manifest only LMW proteinuria and/or hypercalciuria, which are usually asymptomatic. Thirty to 80% of affected males develop end-stage renal disease (ESRD) between ages 30 and 50 years; in some instances ESRD does not develop until the sixth decade of life or later. The disease may also be accompanied by rickets or osteomalacia, growth restriction, and short stature. Disease severity can vary within the same family. Males with Dent disease 2 (caused by pathogenic variants in OCRL) may also have mild intellectual disability, cataracts, and/or elevated muscle enzymes. Due to random X-chromosome inactivation, some female carriers may manifest hypercalciuria and, rarely, renal calculi and moderate LMW proteinuria. Females rarely develop CKD.

Congenital disorders of glycosylation (CDGs) are a genetically heterogeneous group of autosomal recessive disorders caused by enzymatic defects in the synthesis and processing of asparagine (N)-linked glycans or oligosaccharides on glycoproteins. Type I CDGs comprise defects in the assembly of the dolichol lipid-linked oligosaccharide (LLO) chain and its transfer to the nascent protein. These disorders can be identified by a characteristic abnormal isoelectric focusing profile of plasma transferrin (Leroy, 2006). For a discussion of the classification of CDGs, see CDG1A (212065). CDG Ib is clinically distinct from most other CDGs by the lack of significant central nervous system involvement. The predominant symptoms are chronic diarrhea with failure to thrive and protein-losing enteropathy with coagulopathy. Some patients develop hepatic fibrosis. CDG Ib is also different from other CDGs in that it can be treated effectively with oral mannose supplementation, but can be fatal if untreated (Marquardt and Denecke, 2003). Thus, CDG Ib should be considered in the differential diagnosis of patients with unexplained hypoglycemia, chronic diarrhea, liver disease, or coagulopathy in order to allow early diagnosis and effective therapy (Vuillaumier-Barrot et al., 2002) Freeze and Aebi (1999) reviewed CDG Ib and CDG Ic (603147). Marques-da-Silva et al. (2017) systematically reviewed the literature concerning liver involvement in CDG.

Four phenotypes comprise the RRM2B mitochondrial DNA maintenance defects (RRM2B-MDMDs): RRM2B encephalomyopathic MDMD, the most severe phenotype, usually manifesting shortly after birth as hypotonia, poor feeding, and faltering growth requiring hospitalization. Subsequent assessments are likely to reveal multisystem involvement including sensorineural hearing loss, renal tubulopathy, and respiratory failure. Autosomal dominant progressive external ophthalmoplegia (adPEO), typically adult onset; other manifestations can include ptosis, bulbar dysfunction, fatigue, and muscle weakness. RRM2B autosomal recessive progressive external ophthalmoplegia (arPEO), a typically childhood-onset predominantly myopathic phenotype of PEO, ptosis, proximal muscle weakness, and bulbar dysfunction. RRM2B mitochondrial neurogastrointestinal encephalopathy (MNGIE)-like, characterized by progressive ptosis, ophthalmoplegia, gastrointestinal dysmotility, cachexia, and peripheral neuropathy. To date, 78 individuals from 52 families with a molecularly confirmed RRM2B-MDMD have been reported.

Any Fanconi syndrome in which the cause of the disease is a mutation in the SLC34A1 gene.

Proximal tubulopathy-diabetes mellitus-cerebellar ataxia syndrome is characterized by onset of proximal tubulopathy in the first year of life, followed by progressive development during childhood of skin anomalies (erythrocyanosis and abnormal pigmentation), blindness, osteoporosis, cerebellar ataxia, mitochondrial myopathy, deafness and diabetes mellitus.

CDG2L is an autosomal recessive multisystem disorder apparent from birth or early infancy. It is characterized by poor growth, gastrointestinal and liver abnormalities, delayed psychomotor development, hypotonia, recurrent infections, hematologic abnormalities, increased bleeding tendency, and hyperhidrosis or hyperkeratosis. More variable features include nonspecific dysmorphic facial features and cardiac septal defects. The disorder often results in death in infancy or the first years of life (summary by Rymen et al., 2015). For a general discussion of CDGs, see CDG1A (212065) and CDG2A (212066).

Combined oxidative phosphorylation deficiency-55 (COXPD55) is characterized by global developmental delay, hypotonia, short stature, and impaired intellectual development with speech disabilities in childhood. Indolent progressive external ophthalmoplegia phenotype has been described in 1 patient (summary by Olahova et al., 2021). For a discussion of genetic heterogeneity of combined oxidative phosphorylation deficiency, see COXPD1 (609060).