Un caso de grupo sanguíneo raro: fenotipo p / A rare blood group: p phenotype

Un individuo con un fenotipo eritrocitario raro carece de uno o varios antígenos presentes en la mayor parte de la población de pertenencia. Cuando presenta el anticuerpo correspondiente, se pueden producir complicaciones perinatales, transfusionales y/o transplantológicas. Se presenta el caso de una embarazada aloinmunizada derivada a nuestro servicio en la semana 12 de su tercera gesta para su evaluación y seguimiento. El diagnóstico inmunohematológico le asignó el excepcional fenotipo "p" (aproximadamente 1/200 000 individuos), asociado con una mayor tasa de abortos espontáneos y a reacciones transfusionales graves cuando se transfunden unidades incompatibles. El estudio del gen A4GALT demostró la presencia de la mutación c.752C > T en doble dosis. Esta mutación lleva a un cambio de una prolina por una leucina en el residuo 251 de la 4-α-galactosiltransferasa. Por parto inducido por sufrimiento fetal, nace a las 36 semanas una bebé con prueba de antiglobulina (Coombs) directa negativa, eluido reactivo, con ictericia que requirió luminoterapia. Una semana después el neonato fue externado sin secuelas aparentes. Posteriormente, a raíz de una cirugía inminente y la improbabilidad de encontrar sangre compatible, se elaboró un plan para cubrir las posibles demandas. Este caso pone en evidencia la necesidad de contar a nivel nacional con un laboratorio de referencia de inmunohematología y un banco de sangre de grupos raros, que permita resolver con celeridad situaciones que requieran transfundir a estos individuos.

A rare blood group is usually defined as the absence of a high prevalence antigen or the absence of several antigens within a single blood group system. These individuals may develop clinically significant red cell antibodies to the high incidence red cell antigens they lack. A 33-year-old alloimmunized woman was referred to our center at the 12th week of her third pregnancy for evaluation and follow up. The laboratory work-up grouped her as belonging to "p" phenotype, associated with difficulties to find compatible blood for transfusion and a high incidence of recurrent miscarriage. At 36 weeks, a baby girl was born by induced labor due to fetal suffering. With a negative direct antiglobulin test but a positive elution test, she was in the neonatology ward for one week receiving luminotherapy. Homozygosity for a missense mutation at position 752 (c.752C > T) in the A4GALT gene was found to be responsible for the p phenotype. This mutation changes a proline to a leucine at codon 251 of the 4-α-galactosyltransferase. Recently, due to an imminent chirurgical intervention and the impossibility to have compatible blood available for transfusion, an autologous donation plan was designed to satisfy probable demand. This case showed the need for blood bank facilities capable to respond satisfactorily to these situations in Argentina. This would facilitate the storage of cryopreserved blood from individuals with rare blood groups for homologous use or to develop rare blood donors programs.

[A rare blood group: p phenotype]. / Un caso de grupo sanguíneo raro: fenotipo p.

A rare blood group is usually defined as the absence of a high prevalence antigen or the absence of several antigens within a single blood group system. These individuals may develop clinically significant red cell antibodies to the high incidence red cell antigens they lack. A 33-year-old alloimmunized woman was referred to our center at the 12th week of her third pregnancy for evaluation and follow up. The laboratory work-up grouped her as belonging to "p" phenotype, associated with difficulties to find compatible blood for transfusion and a high incidence of recurrent miscarriage. At 36 weeks, a baby girl was born by induced labor due to fetal suffering. With a negative direct antiglobulin test but a positive elution test, she was in the neonatology ward for one week receiving luminotherapy. Homozygosity for a missense mutation at position 752 (c.752C > T) in the A4GALT gene was found to be responsible for the p phenotype. This mutation changes a proline to a leucine at codon 251 of the 4-?-galactosyltransferase. Recently, due to an imminent chirurgical intervention and the impossibility to have compatible blood available for transfusion, an autologous donation plan was designed to satisfy probable demand. This case showed the need for blood bank facilities capable to respond satisfactorily to these situations in Argentina. This would facilitate the storage of cryopreserved blood from individuals with rare blood groups for homologous use or to develop rare blood donors programs.