Cause for recurrent sib death

One full term female newborn delivered vaginally with 2.7 kg birth weight and head circumference 34 cm. Two sibs expired because of sudden death. First female expired at 3 month of age after kept in bed. No reason found. Second female expired at 26 days of life when kept in crib. 3rd was a missed abortion. Present child was normal at birth, had no coarse facial feature, no organomegaly, or any other abnormality. Patient had been investigated after 2 hrs of birth for sepsis screen, blood sugar, calcium which was normal. Total count was high.  Patient had been investigated after 72 hrs for metabolic screen and lactate, ammonia, metabolic workup for galactosemia, G6PD, congenital adrenal hyperplasia were normal. Now patient is 19 days and developed abdominal distension with visible bowel loops. Was admitted in NICU and after 12 hrs patient improved. Next day started feeds, there was no distension. Treated with IV antibiotics After 3 days was discharged. Investigations showed total counts of 23,500; CRP: 24, normal electrolytes and creatinine and X-ray abdomen showed gaseous distension