Hemophilia B is characterized by deficiency in factor IX clotting activity that results in prolonged oozing after injuries, tooth extractions, or surgery, and delayed or recurrent bleeding prior to complete wound healing. The age of diagnosis and frequency of bleeding episodes are related to the level of factor IX clotting activity. In any individual with hemophilia B, bleeding episodes may be more frequent in childhood and adolescence than in adulthood. Individuals with severe hemophilia B are usually diagnosed during the first two years of life. Without prophylactic treatment, they may average up to two to five spontaneous bleeding episodes each month, including spontaneous joint or muscle bleeds, and prolonged bleeding or excessive pain and swelling from minor injuries, surgery, and tooth extractions. Individuals with moderate hemophilia B seldom have spontaneous bleeding, although it varies between individuals; however, they do have prolonged or delayed oozing after relatively minor trauma and are usually diagnosed before age five to six years. The frequency of bleeding episodes varies from once a month to once a year. Individuals with mild hemophilia B do not have spontaneous bleeding episodes; however, without pre- and postoperative treatment, abnormal bleeding occurs with surgery or tooth extractions. The frequency of bleeding may vary from once a year to once every ten years. Individuals with mild hemophilia B are often not diagnosed until later in life. Approximately 30% of heterozygous females have factor IX clotting activity lower than 40% and are at risk for bleeding (even if the affected family member has mild hemophilia B). As in males, bleeding severity generally correlates with factor levels. After major trauma or invasive procedures, prolonged or excessive bleeding usually occurs, regardless of severity.

Hemophilia A is characterized by deficiency in factor VIII clotting activity that results in prolonged bleeding after injuries, tooth extractions, or surgery, and delayed or recurrent bleeding prior to complete wound healing. The age of diagnosis and frequency of bleeding episodes are related to the level of factor VIII clotting activity. Individuals with severe hemophilia A are usually diagnosed during the first two years of life following oral or soft tissue bleeding either with procedures or due to a known family history of hemophilia. Without prophylactic treatment, individuals may average up to two to five spontaneous bleeding episodes each month including spontaneous joint bleeds or deep-muscle hematomas, and prolonged bleeding or excessive pain and swelling from minor injuries, surgery, and tooth extractions. Individuals with moderate hemophilia A seldom have spontaneous bleeding, although it varies between individuals; however, they do have prolonged or delayed bleeding after relatively minor trauma and are usually diagnosed before age five to six years; the frequency of bleeding episodes varies, usually from once a month to once a year. Individuals with mild hemophilia A do not have spontaneous bleeding episodes; however, without pre- and postoperative treatment, abnormal bleeding occurs with surgery or tooth extractions; the frequency of bleeding episodes varies widely, typically from once a year to once every ten years. Individuals with mild hemophilia A are often not diagnosed until later in life. Approximately 30% of heterozygous females have factor VIII clotting activity below 40% and are at risk for bleeding (even if males in the family are only mildly affected). After major trauma or invasive procedures, prolonged or excessive bleeding usually occurs, regardless of severity. In addition, 25% of heterozygous females with normal factor VIII clotting activity report an increased bleeding tendency.

The WAS-related disorders, which include Wiskott-Aldrich syndrome, X-linked thrombocytopenia (XLT), and X-linked neutropenia (XLN), are a spectrum of disorders of hematopoietic cells, with predominant defects of platelets and lymphocytes. Wiskott-Aldrich syndrome usually presents in infancy. Affected males have thrombocytopenia with intermittent mucosal bleeding, bloody diarrhea, and intermittent or chronic petechiae and purpura; recurrent bacterial, viral, fungal, and/or opportunistic infections; and eczema. Approximately 25%-40% of those who survive the early complications develop one or more autoimmune conditions including hemolytic anemia, immune thrombocytopenic purpura, immune-mediated neutropenia, vasculitis, rheumatoid arthritis, and immune-mediated damage to the kidneys and liver. Individuals with a WAS-related disorder, particularly those who have been exposed to Epstein-Barr virus (EBV), are at increased risk of developing lymphomas, which often occur in unusual extranodal locations including the brain, lung, or gastrointestinal tract. Males with XLT have small platelet volume and thrombocytopenia. Severe disease-related events include severe bleeding episodes (14%), autoimmunity (12%), life-threatening infections (7%), and malignancy (5%). Males with XLN typically have congenital neutropenia associated with myelodysplasia, hyperactive neutrophils, increased myeloid cell apoptosis, and lymphoid cell abnormalities.

MED12-related disorders include the phenotypes of FG syndrome type 1 (FGS1), Lujan syndrome (LS), X-linked Ohdo syndrome (XLOS), Hardikar syndrome (HS), and nonspecific intellectual disability (NSID). FGS1 and LS share the clinical findings of cognitive impairment, hypotonia, and abnormalities of the corpus callosum. FGS1 is further characterized by absolute or relative macrocephaly, tall forehead, downslanted palpebral fissures, small and simple ears, constipation and/or anal anomalies, broad thumbs and halluces, and characteristic behavior. LS is further characterized by large head, tall thin body habitus, long thin face, prominent nasal bridge, high narrow palate, and short philtrum. Carrier females in families with FGS1 and LS are typically unaffected. XLOS is characterized by intellectual disability, blepharophimosis, and facial coarsening. HS has been described in females with cleft lip and/or cleft palate, biliary and liver anomalies, intestinal malrotation, pigmentary retinopathy, and coarctation of the aorta. Developmental and cognitive concerns have not been reported in females with HS. Pathogenic variants in MED12 have been reported in an increasing number of males and females with NSID, with affected individuals often having clinical features identified in other MED12-related disorders.

Hereditary hemorrhagic telangiectasia (HHT) is characterized by the presence of multiple arteriovenous malformations (AVMs) that lack intervening capillaries and result in direct connections between arteries and veins. The most common clinical manifestation is spontaneous and recurrent nosebleeds (epistaxis) beginning on average at age 12 years. Telangiectases (small AVMs) are characteristically found on the lips, tongue, buccal and gastrointestinal (GI) mucosa, face, and fingers. The appearance of telangiectases is generally later than epistaxis but may be during childhood. Large AVMs occur most often in the lungs, liver, or brain; complications from bleeding or shunting may be sudden and catastrophic. A minority of individuals with HHT have GI bleeding, which is rarely seen before age 50 years.

Inherited disorders of fibrinogen affect either the quantity (afibrinogenemia and hypofibrinogenemia; 202400) or the quality (dysfibrinogenemia; 616004) of the circulating fibrinogen or both (hypodysfibrinogenemia; see 616004). Afibrinogenemia is characterized by the complete absence of immunoreactive fibrinogen. Bleeding due to afibrinogenemia usually manifests in the neonatal period, with 85% of cases presenting umbilical cord bleeding, but a later age of onst is not unusual. Bleeding may occur in the skin, gastrointestinal tract, genitourinary tract, or the central nervous system, with intracranial hemorrhage being reported as the major cause of death. Patients are susceptible to spontaneous rupture of the spleen. Menstruating women may experience menometrorrhagia. First-trimester abortion is common. Both arterial and venous thromboembolic complications have been reported (summary by de Moerloose and Neerman-Arbez, 2009). Hypofibrinogenemia is characterized by reduced amounts of immunoreactive fibrinogen. Patients are often heterozygous carriers of afibrinogenemia mutations and are usually asymptomatic. However, they may bleed when exposed to trauma or if they have a second associated hemostatic abnormality. Women may experience miscarriages. Liver disease occurs in rare cases (summary by de Moerloose and Neerman-Arbez, 2009).

Most characteristically, Aicardi-Goutières syndrome (AGS) manifests as an early-onset encephalopathy that usually, but not always, results in severe intellectual and physical disability. A subgroup of infants with AGS present at birth with abnormal neurologic findings, hepatosplenomegaly, elevated liver enzymes, and thrombocytopenia, a picture highly suggestive of congenital infection. Otherwise, most affected infants present at variable times after the first few weeks of life, frequently after a period of apparently normal development. Typically, they demonstrate the subacute onset of a severe encephalopathy characterized by extreme irritability, intermittent sterile pyrexias, loss of skills, and slowing of head growth. Over time, as many as 40% develop chilblain skin lesions on the fingers, toes, and ears. It is becoming apparent that atypical, sometimes milder, cases of AGS exist, and thus the true extent of the phenotype associated with pathogenic variants in the AGS-related genes is not yet known.

Autosomal recessive polycystic kidney disease – PKHD1 (ARPKD-PKHD1) is characterized by primary involvement of the kidneys and liver with mostly secondary effects seen in other organ systems. Of the three ages of initial presentation of kidney disease, the two most common are perinatal (i.e., prenatal/neonatal) and infantile (four weeks to age one year) with the classic finding of enlarged kidneys. The major difference between the perinatal and infantile presentations, which typically have similar kidney and liver findings, is the frequent occurrence of pulmonary involvement in the perinatal presentation, which is a major cause of morbidity and mortality in neonates. The less common initial presentation in childhood (after age one year) to young adulthood can be associated with predominant hepatobiliary manifestations characterized by the clinical consequences of developmental anomalies of biliary ductal plate remodeling (also known as Caroli disease). Although the short-term and long-term mortality rates of ARPKD remain significant, the survival of individuals with ARPKD has improved with modern neonatal respiratory support, kidney replacement therapy (KRT) including dialysis and kidney transplantation (KTx), and liver transplantation (LTx) or combined liver and kidney transplantation (CLKTx).

Hereditary hemorrhagic telangiectasia (HHT) is characterized by the presence of multiple arteriovenous malformations (AVMs) that lack intervening capillaries and result in direct connections between arteries and veins. The most common clinical manifestation is spontaneous and recurrent nosebleeds (epistaxis) beginning on average at age 12 years. Telangiectases (small AVMs) are characteristically found on the lips, tongue, buccal and gastrointestinal (GI) mucosa, face, and fingers. The appearance of telangiectases is generally later than epistaxis but may be during childhood. Large AVMs occur most often in the lungs, liver, or brain; complications from bleeding or shunting may be sudden and catastrophic. A minority of individuals with HHT have GI bleeding, which is rarely seen before age 50 years.