Cerebrotendinous xanthomatosis (CTX) is a lipid storage disease characterized by infantile-onset diarrhea, childhood-onset cataract, adolescent- to young adult-onset tendon xanthomas, and adult-onset progressive neurologic dysfunction (dementia, psychiatric disturbances, pyramidal and/or cerebellar signs, dystonia, atypical parkinsonism, peripheral neuropathy, and seizures). Chronic diarrhea from infancy and/or neonatal cholestasis may be the earliest clinical manifestation. In approximately 75% of affected individuals, cataracts are the first finding, often appearing in the first decade of life. Xanthomas appear in the second or third decade; they occur on the Achilles tendon, the extensor tendons of the elbow and hand, the patellar tendon, and the neck tendons. Xanthomas have been reported in the lung, bones, and central nervous system. Some individuals show cognitive impairment from early infancy, whereas the majority have normal or only slightly impaired intellectual function until puberty; dementia with slow deterioration in intellectual abilities occurs in the third decade in more than 50% of individuals. Neuropsychiatric symptoms such as behavioral changes, hallucinations, agitation, aggression, depression, and suicide attempts may be prominent. Pyramidal signs (i.e., spasticity) and/or cerebellar signs almost invariably become evident between ages 20 and 30 years. The biochemical abnormalities that distinguish CTX from other conditions with xanthomas include high plasma and tissue cholestanol concentration, normal-to-low plasma cholesterol concentration, decreased chenodeoxycholic acid (CDCA), increased concentration of bile alcohols and their glyconjugates, and increased concentrations of cholestanol and apolipoprotein B in cerebrospinal fluid.

Glycogen storage disease type I (GSD I) is characterized by accumulation of glycogen and fat in the liver and kidneys resulting in hepatomegaly and nephromegaly. Severely affected infants present in the neonatal period with severe hypoglycemia due to fasting intolerance. More commonly, untreated infants present at age three to four months with hepatomegaly, severe hypoglycemia with or without seizures, lactic acidosis, hyperuricemia, and hypertriglyceridemia. Affected children typically have doll-like faces with full cheeks, relatively thin extremities, short stature, and a protuberant abdomen. Xanthoma and diarrhea may be present. Impaired platelet function and development of reduced or dysfunctional von Willebrand factor can lead to a bleeding tendency with frequent epistaxis and menorrhagia in females. Individuals with untreated GSD Ib are more likely to develop impaired neutrophil and monocyte function as well as chronic neutropenia resulting in recurrent bacterial infections, gingivitis, periodontitis, and genital and intestinal ulcers. Long-term complications of untreated GSD I include short stature, osteoporosis, delayed puberty, renal disease (including proximal and distal renal tubular acidosis, renal stones, and kidney failure), gout, systemic hypertension, pulmonary hypertension, hepatic adenomas with potential for malignancy, pancreatitis, and polycystic ovaries. Seizures and cognitive impairment may occur in individuals with prolonged periods of hypoglycemia. Normal growth and puberty are expected in treated children. Most affected individuals live into adulthood.

The phenotype of acid sphingomyelinase deficiency (ASMD) occurs along a continuum. Individuals with the severe early-onset form, infantile neurovisceral ASMD, were historically diagnosed with Niemann-Pick disease type A (NPD-A). The later-onset, chronic visceral form of ASMD is also referred to as Niemann-Pick disease type B (NPD-B). A phenotype with intermediate severity is also known as chronic neurovisceral ASMD (NPD-A/B). Enzyme replacement therapy (ERT) is currently FDA approved for the non-central nervous system manifestations of ASMD, regardless of type. As more affected individuals are treated with ERT for longer periods of time, the natural history of ASMD is likely to change. The most common presenting symptom in untreated NPD-A is hepatosplenomegaly, usually detectable by age three months; over time the liver and spleen become massive in size. Growth failure typically becomes evident by the second year of life. Psychomotor development progresses no further than the 12-month level, after which neurologic deterioration is relentless. This feature may not be amenable to ERT. A classic cherry-red spot of the macula of the retina, which may not be present in the first few months, is eventually present in all affected children, although it is unclear if ERT will have an impact on this. Interstitial lung disease caused by storage of sphingomyelin in pulmonary macrophages results in frequent respiratory infections and often respiratory failure. Most untreated children succumb before the third year of life. NPD-B generally presents later than NPD-A, and the manifestations are less severe. NPD-B is characterized in untreated individuals by progressive hepatosplenomegaly, gradual deterioration in liver and pulmonary function, osteopenia, and atherogenic lipid profile. No central nervous system manifestations occur. Individuals with NPD-A/B have symptoms that are intermediate between NPD-A and NPD-B. The presentation in individuals with NPD-A/B varies greatly, although all are characterized by the presence of some central nervous system manifestations. Survival to adulthood can occur in individuals with NPD-B and NPD-A/B, even when untreated.

Glycogenosis due to glucose-6-phosphatase deficiency (G6P) type b, or glycogen storage disease (GSD) type 1b, is a type of glycogenosis due to G6P deficiency (see this term).

Familial partial lipodystrophy type 1 (FPLD1), or Kobberling-type lipodystrophy, is characterized by loss of adipose tissue confined to the extremities, with normal or increased distribution of fat on the face, neck, and trunk (Kobberling and Dunnigan, 1986). For a general description and a discussion of genetic heterogeneity of familial partial lipodystrophy (FPLD), see 151660.

Familial partial lipodystrophy (FPLD) is a metabolic disorder characterized by abnormal subcutaneous adipose tissue distribution beginning in late childhood or early adult life. Affected individuals gradually lose fat from the upper and lower extremities and the gluteal and truncal regions, resulting in a muscular appearance with prominent superficial veins. In some patients, adipose tissue accumulates on the face and neck, causing a double chin, fat neck, or cushingoid appearance. Metabolic abnormalities include insulin-resistant diabetes mellitus with acanthosis nigricans and hypertriglyceridemia; hirsutism and menstrual abnormalities occur infrequently. Familial partial lipodystrophy may also be referred to as lipoatrophic diabetes mellitus, but the essential feature is loss of subcutaneous fat (review by Garg, 2004). The disorder may be misdiagnosed as Cushing disease (see 219080) (Kobberling and Dunnigan, 1986; Garg, 2004). Genetic Heterogeneity of Familial Partial Lipodystrophy Familial partial lipodystrophy is a clinically and genetically heterogeneous disorder. Types 1 and 2 were originally described as clinical subtypes: type 1 (FPLD1; 608600), characterized by loss of subcutaneous fat confined to the limbs (Kobberling et al., 1975), and FPLD2, characterized by loss of subcutaneous fat from the limbs and trunk (Dunnigan et al., 1974; Kobberling and Dunnigan, 1986). No genetic basis for FPLD1 has yet been delineated. FPLD3 (604367) is caused by mutation in the PPARG gene (601487) on chromosome 3p25; FPLD4 (613877) is caused by mutation in the PLIN1 gene (170290) on chromosome 15q26; FPLD5 (615238) is caused by mutation in the CIDEC gene (612120) on chromosome 3p25; FPLD6 (615980) is caused by mutation in the LIPE gene (151750) on chromosome 19q13; FPLD7 (606721) is caused by mutation in the CAV1 gene (601047) on chromosome 7q31; FPLD8 (620679), caused by mutation in the ADRA2A gene (104210) on chromosome 10q25; and FPLD9 (620683), caused by mutation in the PLAAT3 gene (613867) on chromosome 11q12.

Glycogen storage disease type I (GSD I) is characterized by accumulation of glycogen and fat in the liver and kidneys resulting in hepatomegaly and nephromegaly. Severely affected infants present in the neonatal period with severe hypoglycemia due to fasting intolerance. More commonly, untreated infants present at age three to four months with hepatomegaly, severe hypoglycemia with or without seizures, lactic acidosis, hyperuricemia, and hypertriglyceridemia. Affected children typically have doll-like faces with full cheeks, relatively thin extremities, short stature, and a protuberant abdomen. Xanthoma and diarrhea may be present. Impaired platelet function and development of reduced or dysfunctional von Willebrand factor can lead to a bleeding tendency with frequent epistaxis and menorrhagia in females. Individuals with untreated GSD Ib are more likely to develop impaired neutrophil and monocyte function as well as chronic neutropenia resulting in recurrent bacterial infections, gingivitis, periodontitis, and genital and intestinal ulcers. Long-term complications of untreated GSD I include short stature, osteoporosis, delayed puberty, renal disease (including proximal and distal renal tubular acidosis, renal stones, and kidney failure), gout, systemic hypertension, pulmonary hypertension, hepatic adenomas with potential for malignancy, pancreatitis, and polycystic ovaries. Seizures and cognitive impairment may occur in individuals with prolonged periods of hypoglycemia. Normal growth and puberty are expected in treated children. Most affected individuals live into adulthood.