Genotype-phenotype correlation in children with hereditary spherocytosis.

Hereditary spherocytosis (HS) is a common inherited haemolytic anaemia attributed to disturbances in five different red cell membrane proteins. We performed a retrospective study of 166 children with HS and describe the clinical phenotype according to the genotype. In 160/166 (97%) children with HS a disease-causing mutation was identified. Pathogenic variants in ANK1, SPTB, SLC4A1 and SPTA1 were found in 49%, 33%, 13% and 5% of patients. Children with SLC4A1-HS had the mildest phenotype, showing the highest haemoglobin (P < 0·001), lowest reticulocyte counts (P < 0·001) and lowest unconjugated bilirubin levels (P = 0·006), and none required splenectomy in childhood (P < 0·001). Conversely, children with autosomal recessive SPTA1-HS had the most severe clinical phenotype, with almost all patients undergoing splenectomy in early childhood. Patients with ANK1 and SPTB variants showed a similar clinical phenotype. Within each gene, variant type or location did not predict disease severity or likelihood of splenectomy. Among patients with a genetic diagnosis, 47 (29%) underwent splenectomy (23 partial; 24 total) while 57 (36%) underwent cholecystectomy. Total splenectomy led to greater improvements in haemoglobin (P = 0·02). Select use of genetic testing (especially in patients without a family history) may help predict clinical phenotype in childhood and guide family counselling.

Megakaryocyte and platelet abnormalities in a patient with a W33C mutation in the conserved SH3-like domain of myosin heavy chain IIA.

Heterozygous mutations in MYH9, which encodes non-muscle myosin heavy chain IIA (MHC-IIA), result in autosomal dominant inherited MYH9-related disorders characterised by macro-thrombocytopenia, granulocyte inclusions, variable sensorineural deafness, cataracts and nephritis. MHC-IIA is assembled into a complex consisting of two pairs of light chains and two heavy chains, where the latter contain a neck region, SH3-like, motor and rod domains. We describe a patient with a Trp33Cys missense mutation in the SH3-like domain of MHC-IIA. Abnormal platelet function was observed using platelet aggregometry with the agonists epinephrine and adenosine diphosphate (ADP). Patient granulocytes and megakaryocytes, but not platelets, contained abnormal MHC-IIA inclusions visualised by confocal immunofluorescence or electron microscopy. Megakaryocytes grown in culture were smaller and contained hypolobulated nuclei compared to controls. Bone marrow-derived megakaryocytes revealed a preponderance of immature forms, the presence of structurally diverse inclusion bodies, and frequent emperipolesis as assessed by electron microscopy. Platelets and leukocytes contained indistinguishable amounts of total MHC-IIA determined by immunoblotting. Molecular modelling studies indicated that mutation of Trp33 destabilises the interface between the SH3-like and motor domain of MHC-IIA, which is close to previously described motor domain mutations, implying an important structural and/or functional role for this region in MHC-IIA.

Laparoscopic partial vs total splenectomy in children with hereditary spherocytosis.

BACKGROUND: Open partial splenectomy provides reversal of anemia and relief of symptomatic splenomegaly while theoretically retaining splenic immune function for hereditary spherocytosis. We recently developed a laparoscopic approach for partial splenectomy. The purpose of the present study is to compare the outcomes in a group of patients undergoing laparoscopic partial splenectomy (LPS) with those in a group of children undergoing laparoscopic total splenectomy (LTS) over the same period. METHODS: Systematic chart review was conducted of all children with hereditary spherocytosis who had LTS or LPS from 2000 to 2006 at the Hospital for Sick Children, Toronto, Ontario, Canada. T tests were used for continuous data, and chi(2) for proportional data; P value of less than .05 was considered significant. RESULTS: There were 9 patients (14 males) in each group. Groups were similar in sex, age, concomitant cholecystectomy, and preoperative hospitalizations, transfusions, and spleen size. Estimated blood loss was greater in the LPS group (188 + 53 vs 67 + 17 mL; P = .02), but transfusion requirements were similar (1/9 vs 0/9). Complication rate was similar between groups. The LPS group had higher morphine use (4.1 + 0.6 vs 2.4 + 0.2 days; P = .03), greater time to oral intake (4.4 + 0.7 vs 2.0 + 0.2 days; P = .01), and longer hospital stay (6.3 + 1.0 vs 2.7 + 0.3 days; P = .005) than the LTS group. Nuclear scan 6 to 8 weeks postoperatively demonstrated residual perfused splenic tissue in all LPS patients. No completion splenectomy was necessary after a mean follow-up of 25 months. CONCLUSION: These data suggest that LPS is as effective as LTS for control of symptoms. However, LPS is associated with more pain, longer time to oral intake, and longer hospital stay. These disadvantages may be balanced by retained splenic immune function, but further studies are required to assess long-term splenic function in these patients.

The prevention and treatment of bacterial infections in children with asplenia or hyposplenia: practice considerations at the Hospital for Sick Children, Toronto.

Children born without a spleen or who have impaired splenic function, due to disease or splenectomy, are at significantly increased risk of life-threatening bacterial sepsis. The mainstays of prevention are education, immunization, and prophylactic antibiotics. The availability of conjugate 7-valent pneumococcal vaccines for use in children to age 9 years at least, as well as conjugate meningococcal C vaccine in some countries, for use beginning in infancy, appear to represent beneficial additions, but not substitutions, to previous recommendations for the use of polysaccharide 23-valent pneumococcal and quadrivalent A, C, Y, W-135 vaccines. Routine immunization against H. influenzae type b should continue with non-immunized children older than age 5 years receiving two doses 2 months apart, similar to children who have not previously received conjugate pneumococcal vaccine in infancy. Annual influenza immunization, which reduces the risk of secondary bacterial infection, is also recommended for asplenic children and their household contacts. Many experts continue prophylaxis indefinitely although prophylaxis of the penicillin allergic child remains suboptimal.

Assessment of thrombocytopenic disorders using the Platelet Function Analyzer (PFA-100).

The Platelet Function Analyzer (PFA-100) was used to measure platelet function in paediatric patients with destructive versus underproduction thrombocytopenia. Closure time (CT) and total volume (TV) measurements with standard 150 microm apertures discriminated between patients with similar platelet counts from 30 to 150 x 10(9)/l. However, at platelet counts < 30 x 10(9)/l, a 100-microm aperture (experimental) gave the best assessment of platelet function. TV results could be analysed even when CTs were indeterminate. Further investigations are warranted to more fully understand the relationships among platelet function as measured by the PFA-100 in standard/experimental modes, bleeding and transfusion outcome in thrombocytopenia.